1.
Geologic time scale
–
The table of geologic time spans, presented here, agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy. Evidence from radiometric dating indicates that Earth is about 4.54 billion years old, the geology or deep time of Earth’s past has been organized into various units according to events which took place in each period. Older time spans, which predate the reliable record, are defined by their absolute age. Some other planets and moons within the Solar System have sufficiently rigid structures to have preserved records of their own histories, for example, Venus, Mars, dominantly fluid planets, such as the gas giants, do not preserve their history in a comparable manner. Apart from the Late Heavy Bombardment, events on other planets probably had little influence on the Earth. Construction of a scale that links the planets is, therefore, of only limited relevance to the Earths time scale. The existence, timing, and terrestrial effects of the Late Heavy Bombardment is still debated, the largest defined unit of time is the supereon, composed of eons. Eons are divided into eras, which are in turn divided into periods, epochs, the terms eonothem, erathem, system, series, and stage are used to refer to the layers of rock that correspond to these periods of geologic time in Earths history. Geologists qualify these units as early, mid, and late when referring to time, and lower, middle, for example, the lower Jurassic Series in chronostratigraphy corresponds to the early Jurassic Epoch in geochronology. The adjectives are capitalized when the subdivision is formally recognized, and lower case when not, thus early Miocene but Early Jurassic. Geologic units from the time but different parts of the world often look different and contain different fossils. For example, in North America the Lower Cambrian is called the Waucoban series that is subdivided into zones based on succession of trilobites. In East Asia and Siberia, the unit is split into Alexian, Atdabanian. A key aspect of the work of the International Commission on Stratigraphy is to reconcile this conflicting terminology, the term Anthropocene is used informally by popular culture and a growing number of scientists to describe the current epoch in which we are living. The term was coined by Paul Crutzen and Eugene Stoermer in 2000 to describe the current time, others say that humans have not even started to leave their biggest impact on Earth, and therefore the Anthropocene hasnt even started yet. Whatever the case, the ICS has not officially approved the term, leonardo da Vinci concurred with Aristotles interpretation that fossils represented the remains of ancient life. The 11th-century Persian geologist Avicenna and the 13th-century Dominican bishop Albertus Magnus extended Aristotles explanation into a theory of a petrifying fluid. Avicenna also first proposed one of the principles underlying geologic time scales, the Chinese naturalist Shen Kuo also recognized the concept of deep time
Geologic time scale
–
Key concepts
Geologic time scale
2.
Proterozoic
–
The Proterozoic is a geological eon representing the time just before the proliferation of complex life on Earth. The name Proterozoic comes from Greek and means life, the Greek root protero-, means former, earlier and zoic-, means animal. The Proterozoic Eon extended from 2500 Ma to 541 Ma, and is the most recent part of the Precambrian Supereon and it is subdivided into three geologic eras, the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic. The geologic record of the Proterozoic Eon is more complete than that for the preceding Archean Eon, studies of these rocks have shown that the eon continued the massive continental accretion that had begun late in the Archean Eon. The Proterozoic Eon also featured the first definitive supercontinent cycles and wholly modern mountain building activity, there is evidence that the first known glaciations occurred during the Proterozoic. One of the most important events of the Proterozoic was the accumulation of oxygen in the Earths atmosphere, until roughly 2.3 billion years ago, oxygen was probably only 1% to 2% of its current level. The Banded iron formations, which provide most of the iron ore, are one mark of that mineral sink process. Their accumulation ceased after 1.9 billion years ago, after the iron in the oceans had all been oxidized, red beds, which are colored by hematite, indicate an increase in atmospheric oxygen 2 billion years ago. Such massive iron oxide formations are not found in older rocks, the Proterozoic Eon was a very tectonically active period in the Earth’s history. The late Archean Eon to Early Proterozoic Eon corresponds to a period of increasing crustal recycling, suggesting subduction, evidence for this increased subduction activity comes from the abundance of old granites originating mostly after 2.6 Ga. The appearance of eclogites, which metamorphic rocks created by pressure, are explained using a model that incorporates subduction. As a result of remelting of basaltic oceanic crust due to subduction, the long-term tectonic stability of those cratons is why we find continental crust ranging up to a few billion years in age. It is believed that 43% of modern continental crust was formed in the Proterozoic, 39% formed in the Archean, studies by Condie 2000 and Rino et al.2004 suggest that crust production happened episodically. By isotopically calculating the ages of Proterozoic granitoids it was determined there were several episodes of rapid increase in continental crust production. The reason for these pulses is unknown, but they seemed to have decreased in magnitude after every period, evidence of collision and rifting between continents raises the question as to what exactly were the movements of the Archean cratons composing Proterozoic continents. Paleomagnetic and geochronological dating mechanisms have allowed the deciphering of Precambrian Supereon tectonics and it is known that tectonic processes of the Proterozoic Eon resemble greatly the evidence of tectonic activity, such as orogenic belts or ophiolite complexes, we see today. Hence, most geologists would conclude that the Earth was active at that time and it is also commonly accepted that during the Precambrian, the Earth went through several supercontinent breakup and rebuilding cycles. In the late Proterozoic, the dominant supercontinent was Rodinia and it consisted of a series of continents attached to a central craton that forms the core of the North American Continent called Laurentia
Proterozoic
–
Lower Proterozoic
stromatolites from Bolivia, South America
Proterozoic
–
Stromatolites (Proterozoic) Zebra River Canyon, Western Namibia
3.
Phanerozoic
–
The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 541 million years to the present, and began with the Cambrian Period when diverse hard-shelled animals first appeared. Its name was derived from the Ancient Greek words φανερός and ζωή, meaning life, since it was once believed that life began in the Cambrian. The time before the Phanerozoic, called the Precambrian supereon, is now divided into the Hadean, Archaean, land plant life appeared in the early Phanerozoic eon. During this time span, tectonic forces caused the continents to move and eventually collect into a landmass known as Pangaea. The Proterozoic-Phanerozoic boundary is at 541 million years ago, the three different dividing points are within a few million years of each other. The Phanerozoic is divided into three eras, the Paleozoic, Mesozoic, and Cenozoic, which are subdivided into 12 periods. The Paleozoic features the rise of fish, amphibians and reptiles, the Mesozoic is ruled by the reptiles, and features the evolution of mammals, birds and more famously, dinosaurs. The Cenozoic is the time of the mammals, and more recently, the Paleozoic is a time in Earths history when complex life forms evolved, took their first breath of oxygen on dry land, and when the forerunners of all life on Earth began to diversify. There are six periods in the Paleozoic era, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, the Cambrian is the first period of the Paleozoic Era and starts from 541 to 485 million years ago. The Cambrian sparked a rapid expansion in evolution in an event known as the Cambrian Explosion during which the greatest number of creatures evolved in a period in the history of Earth. Plants like algae evolved, and the fauna was dominated by armored arthropods, almost all marine phyla evolved in this period. During this time, the super-continent Pannotia began to break up, the Ordovician spans from 485 million years to 440 million years. The Ordovician was a time in Earths history in many species still prevalent today evolved, such as primitive fish, cephalopods. The most common forms of life, however, were trilobites, snails, more importantly, the first arthropods crept ashore to colonize Gondwana, a continent empty of animal life. By the end of the Ordovican, Gondwana had moved from the equator to the South Pole, the glaciation of Gondwana resulted in a major drop in sea level, killing off all life that had established along its coast. Glaciation caused a snowball Earth, leading to the Ordovician-Silurian extinction, during which 60% of marine invertebrates and this is considered the first mass extinction and the second deadliest in the history of Earth. The Silurian spans from 440 million years to 415 million years, fully terrestrial life evolved, which included early arachnids, fungi, and centipedes
Phanerozoic
–
Trilobites
Phanerozoic
–
Cephalaspis (a jaw-less fish)
Phanerozoic
–
Eogyrinus (an amphibian) of the Carboniferous
Phanerozoic
–
Dimetrodon
4.
Eoarchean
–
The Eoarchean is the first era of the Archean Eon of the geologic record for which the Earth has a solid crust. It spans 400 million years from the end of the Hadean Eon 4000 million years ago to the start of the Paleoarchean Era 3600 Mya, the abiotic origins of life have been dated to this era and evidence of cyanobacteria date to 3500 Mya, just outside of this era. At that time atmosphere was without oxygen and the pressure values ranged from 10 to 100 bar, the Eoarchean was formerly officially unnamed and informally referred to as the first part of the Early Archean or Paleoarchean Era, both now obsolete names. The Eoarchaeans lower boundary or starting point of 4 Gya is officially recognized by the International Commission on Stratigraphy, the name comes from two Greek words, eos and archaios. The first supercontinent Vaalbara appeared around the end of this period at about 3,600 million years ago, a characteristic of the Eoarchean is that Earth possessed a firm crust for the first time. However, this crust may have been incomplete at many sites, the beginning of the Eoarchean is characterized by heavy asteroid bombardment within the inner solar system, the Late Heavy Bombardment. The Eoarchean is the first time from which solid rock formations on Earth have survived, the largest is the Isua Greenstone Belt on the south-west coast of Greenland and dates from 3.8 billion years. The Acasta Gneiss within the Canadian Shield have been dated to be 4,030 Ma and are therefore the oldest preserved rock formations. In 2008, another rock formation was discovered in the Nuvvuagittuq greenstone belt in northern Québec Canada which has dated to be 4,280 million years ago. These formations are presently under intense investigation,3,850 million years old Greenland apatite shows evidence of 12C enrichment. This has sparked a debate whether there might have been photosynthetic life before 3.8 billion years, origins of Life, The Primal Self-Organization. Media related to Eoarchean at Wikimedia Commons Taxonconcept. stratigraphy. ne, A short fact sheet on the Eoarchean
Eoarchean
–
Garnet
paragneiss, Nuvvuagittuq Greenstone Belt, Canada. 4.28 Ga old: the oldest known Earth rock of which direct samples are available.
Eoarchean
–
Eoarchaean (3.8 b.y.) Greenlandite specimen (fuchsite-quartz gneiss),
Nuup Kangerlua, Greenland.
5.
Paleozoic
–
The Paleozoic Era is the earliest of three geologic eras of the Phanerozoic Eon, from 541 to 252.17 million years ago. It is the longest of the Phanerozoic eras, and is subdivided into six periods, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous. The Paleozoic comes after the Neoproterozoic era of the Proterozoic and is followed by the Mesozoic, the Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earths history, known as the Cambrian explosion, fish, arthropods, amphibians, anapsids, synapsids, euryapsids and diapsids all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, Great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. Towards the end of the era, large, sophisticated diapsids and synapsids were dominant, the Paleozoic Era ended with the largest extinction event in the history of Earth, the Permian–Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic Era to recover, recovery of life in the sea may have been much faster. The Paleozoic era began and ended with supercontinents and in between were the rise of mountains along the margins, and flooding and draining of shallow seas between. At its start, the supercontinent Pannotia broke up, paleoclimatic studies and evidence of glaciers indicate that central Africa was most likely in the polar regions during the early Paleozoic. During the early Paleozoic, the huge continent Gondwana formed or was forming, by mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. There are six periods in the Paleozoic Era, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, the Cambrian spans from 541 million years to 485 million years and is the first period of the Paleozoic era of the Phanerozoic. The Cambrian marked a boom in evolution in an event known as the Cambrian explosion in which the largest number of creatures evolved in any period of the history of the Earth. Creatures like algae evolved, but the most ubiquitous of that period were the armored arthropods, almost all marine phyla evolved in this period. During this time, the supercontinent Pannotia begins to break up, the Ordovician spanned from 485 million years to 443 million years ago. The Ordovician is a time in Earths history in many of the biological classes still prevalent today evolved, such as primitive fish, cephalopods. The most common forms of life, however, were trilobites, snails, more importantly, the first arthropods went ashore to colonize the empty continent of Gondwana. By the end of the Ordovican, Gondwana was at the pole, early North America had collided with Europe. Glaciation of Africa resulted in a drop in sea level
Paleozoic
–
Trilobites
Paleozoic
–
Cephalaspis (a jawless fish)
Paleozoic
–
Eogyrinus (an amphibian) of the Carboniferous
Paleozoic
–
Dimetrodon
6.
Mesozoic
–
The Mesozoic Era is an interval of geological time from about 252 to 66 million years ago. This Era is also called from a paleobotanist view the Age of Conifers, Mesozoic means middle life, deriving from the Greek prefix meso-/μεσο- for between and zōon/ζῷον meaning animal or living being. It is one of three eras of the Phanerozoic Eon, preceded by the Paleozoic and succeeded by the Cenozoic. The era is subdivided into three periods, the Triassic, Jurassic, and Cretaceous, which are further subdivided into a number of epochs. The Mesozoic was a time of significant tectonic, climate and evolutionary activity, the era witnessed the gradual rifting of the supercontinent Pangaea into separate landmasses that would eventually move into their current positions. The climate of the Mesozoic was varied, alternating between warming and cooling periods, overall, however, the Earth was hotter than it is today. Birds first appeared in the Jurassic, having evolved from a branch of theropod dinosaurs, the first mammals also appeared during the Mesozoic, but would remain small—less than 15 kg —until the Cenozoic. Following the Paleozoic, the Mesozoic extended roughly 186 million years and this time frame is separated into three geologic periods. It is also known as the Great Dying because it is considered the largest mass extinction in the Earths history, the upper boundary of the Mesozoic is set at the Cretaceous–Paleogene extinction event, which may have been caused by the impactor that created Chicxulub Crater on the Yucatán Peninsula. Towards the Late Cretaceous large volcanic eruptions are believed to have contributed to the Cretaceous–Paleogene extinction event. Approximately 50% of all genera became extinct, including all of the non-avian dinosaurs, the Triassic ranges roughly from 252 million to 201 million years ago. The Triassic is a time in Earths history bracketed between the Permian Extinction and the Triassic–Jurassic extinction event, two of the big five, and precedes the Jurassic Period and it has three major epochs, the Early Triassic, the Middle Triassic and the Late Triassic. The Early Triassic was between about 252 million to 247 million years ago and was dominated by deserts as Pangaea had not yet broken up, thus the interior was nothing, the Earth had just witnessed a massive die-off in which 95% of all life became extinct. The most common life on earth were Lystrosaurus, labyrinthodonts. Temnospondyls evolved during this time and would be the dominant predator for much of the Triassic, the Middle Triassic spans roughly from 247 million to 237 million years ago. The Middle Triassic featured the beginnings of the breakup of Pangaea, the ecosystem had recovered from the devastation that was the Great Dying. Algae, sponge, corals, and crustaceans all had recovered, new aquatic reptiles evolved, such as ichthyosaurs and nothosaurs. Meanwhile, on land, pine forests flourished, as did groups of insects like mosquitoes, the first ancient crocodilians evolved, which sparked competition with the large amphibians that had since ruled the freshwater world
Mesozoic
–
Plateosaurus (a
prosauropod)
Mesozoic
–
Rhamphorhynchus
Mesozoic
–
(Inaccurately portrayed)
Stegosaurus
Mesozoic
–
Tylosaurus (a
mosasaur) hunting
Xiphactinus
7.
Cenozoic
–
The Cenozoic Era is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and covering the period from 66 million years ago to the present day. The Cenozoic is also known as the Age of Mammals, because of the mammals that dominated, such as Entelodont, Paraceratherium. The extinction of many large groups such as non-avian dinosaurs, Plesiosauria and Pterosauria allowed the mammals and birds to greatly diversify. Early in the Cenozoic, following the K-Pg event, the planet was dominated by relatively small fauna, including mammals, birds, reptiles. From a geological perspective, it did not take long for mammals, some flightless birds grew larger than humans. These species are referred to as terror birds, and were formidable predators. Mammals came to occupy almost every available niche, and some also grew very large, the Earths climate had begun a drying and cooling trend, culminating in the glaciations of the Pleistocene Epoch, and partially offset by the Paleocene-Eocene Thermal Maximum. The continents also began looking roughly familiar at this time and moved into their current positions. The Cenozoic is divided into three periods, the Paleogene, Neogene, and Quaternary, and seven epochs, the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene. The common use of epochs during the Cenozoic helps paleontologists better organize, there is also more detailed knowledge of this era than any other because of the relatively young, well-preserved rocks associated with it. The Paleogene spans from the extinction of dinosaurs,66 million years ago. It features three epochs, the Paleocene, Eocene and Oligocene, the Paleocene ranged from 66 million to 56 million years ago. The Paleocene is a point between the devastation that is the K-T extinction, to the rich jungles environment that is the Early Eocene. The Early Paleocene saw the recovery of the earth, the continents began to take their modern shape, but all the continents and subcontinent India were separated from each other. Afro-Eurasia was separated by the Tethys Sea, and the Americas were separated by the strait of Panama and this epoch featured a general warming trend, with jungles eventually reaching the poles. The oceans were dominated by sharks as the large reptiles that had once ruled became extinct, archaic mammals filled the world such as creodonts and early primates that evolved during the Mesozoic, and as a result, there was nothing over 10 kilograms. The Eocene Epoch ranged from 56 million years to 33.9 million years ago, in the Early-Eocene, life was small and lived in cramped jungles, much like the Paleocene. There was nothing over the weight of 10 kilograms, among them were early primates, whales and horses along with many other early forms of mammals
Cenozoic
–
Basilosaurus
Cenozoic
–
Animals of the Miocene (
Chalicotherium,
Hyenadon,
Entelodont...). Mammals are the dominant terrestrial vertebrates of the Cenozoic.
Cenozoic
–
Megafauna of the Pleistocene (
mammoths,
cave lions,
woolly rhino,
Megaloceros, American
horses)
8.
Cartesian coordinate system
–
Each reference line is called a coordinate axis or just axis of the system, and the point where they meet is its origin, usually at ordered pair. The coordinates can also be defined as the positions of the projections of the point onto the two axis, expressed as signed distances from the origin. One can use the principle to specify the position of any point in three-dimensional space by three Cartesian coordinates, its signed distances to three mutually perpendicular planes. In general, n Cartesian coordinates specify the point in an n-dimensional Euclidean space for any dimension n and these coordinates are equal, up to sign, to distances from the point to n mutually perpendicular hyperplanes. The invention of Cartesian coordinates in the 17th century by René Descartes revolutionized mathematics by providing the first systematic link between Euclidean geometry and algebra. Using the Cartesian coordinate system, geometric shapes can be described by Cartesian equations, algebraic equations involving the coordinates of the points lying on the shape. For example, a circle of radius 2, centered at the origin of the plane, a familiar example is the concept of the graph of a function. Cartesian coordinates are also tools for most applied disciplines that deal with geometry, including astronomy, physics, engineering. They are the most common system used in computer graphics, computer-aided geometric design. Nicole Oresme, a French cleric and friend of the Dauphin of the 14th Century, used similar to Cartesian coordinates well before the time of Descartes. The adjective Cartesian refers to the French mathematician and philosopher René Descartes who published this idea in 1637 and it was independently discovered by Pierre de Fermat, who also worked in three dimensions, although Fermat did not publish the discovery. Both authors used a single axis in their treatments and have a length measured in reference to this axis. The concept of using a pair of axes was introduced later, after Descartes La Géométrie was translated into Latin in 1649 by Frans van Schooten and these commentators introduced several concepts while trying to clarify the ideas contained in Descartes work. Many other coordinate systems have developed since Descartes, such as the polar coordinates for the plane. The development of the Cartesian coordinate system would play a role in the development of the Calculus by Isaac Newton. The two-coordinate description of the plane was later generalized into the concept of vector spaces. Choosing a Cartesian coordinate system for a one-dimensional space – that is, for a straight line—involves choosing a point O of the line, a unit of length, and an orientation for the line. An orientation chooses which of the two half-lines determined by O is the positive, and which is negative, we say that the line is oriented from the negative half towards the positive half
Cartesian coordinate system
–
The
right hand rule.
Cartesian coordinate system
–
Illustration of a Cartesian coordinate plane. Four points are marked and labeled with their coordinates: (2,3) in green, (−3,1) in red, (−1.5,−2.5) in blue, and the origin (0,0) in purple.
Cartesian coordinate system
–
3D Cartesian Coordinate Handedness
9.
Eon (geology)
–
The table of geologic time spans, presented here, agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy. Evidence from radiometric dating indicates that Earth is about 4.54 billion years old, the geology or deep time of Earth’s past has been organized into various units according to events which took place in each period. Older time spans, which predate the reliable record, are defined by their absolute age. Some other planets and moons within the Solar System have sufficiently rigid structures to have preserved records of their own histories, for example, Venus, Mars, dominantly fluid planets, such as the gas giants, do not preserve their history in a comparable manner. Apart from the Late Heavy Bombardment, events on other planets probably had little influence on the Earth. Construction of a scale that links the planets is, therefore, of only limited relevance to the Earths time scale. The existence, timing, and terrestrial effects of the Late Heavy Bombardment is still debated, the largest defined unit of time is the supereon, composed of eons. Eons are divided into eras, which are in turn divided into periods, epochs, the terms eonothem, erathem, system, series, and stage are used to refer to the layers of rock that correspond to these periods of geologic time in Earths history. Geologists qualify these units as early, mid, and late when referring to time, and lower, middle, for example, the lower Jurassic Series in chronostratigraphy corresponds to the early Jurassic Epoch in geochronology. The adjectives are capitalized when the subdivision is formally recognized, and lower case when not, thus early Miocene but Early Jurassic. Geologic units from the time but different parts of the world often look different and contain different fossils. For example, in North America the Lower Cambrian is called the Waucoban series that is subdivided into zones based on succession of trilobites. In East Asia and Siberia, the unit is split into Alexian, Atdabanian. A key aspect of the work of the International Commission on Stratigraphy is to reconcile this conflicting terminology, the term Anthropocene is used informally by popular culture and a growing number of scientists to describe the current epoch in which we are living. The term was coined by Paul Crutzen and Eugene Stoermer in 2000 to describe the current time, others say that humans have not even started to leave their biggest impact on Earth, and therefore the Anthropocene hasnt even started yet. Whatever the case, the ICS has not officially approved the term, leonardo da Vinci concurred with Aristotles interpretation that fossils represented the remains of ancient life. The 11th-century Persian geologist Avicenna and the 13th-century Dominican bishop Albertus Magnus extended Aristotles explanation into a theory of a petrifying fluid. Avicenna also first proposed one of the principles underlying geologic time scales, the Chinese naturalist Shen Kuo also recognized the concept of deep time
Eon (geology)
–
Key concepts
Eon (geology)
10.
Earth
–
Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
Earth
–
"
The Blue Marble " photograph of Earth, taken during the
Apollo 17 lunar mission in 1972
Earth
–
Artist's impression of the early Solar System's planetary disk
Earth
–
World map color-coded by relative height
Earth
–
The summit of
Chimborazo, in Ecuador, is the point on Earth's surface farthest from its center.
11.
Geologist
–
A geologist is a scientist who studies the solid and liquid matter that constitutes the Earth as well as the processes that shape it. Geologists usually study geology, although backgrounds in physics, chemistry, biology, field work is an important component of geology, although many subdisciplines incorporate laboratory work. Some geologists work in the mining business searching for metals, oils and they are also in the forefront of natural hazards and disasters prevention and mitigation, studying natural hazards such as earthquakes, volcanic activity, tsunamis, weather storms. Their studies are used to warn the public of the occurrence of these events. Geologists are also important contributors to climate change discussions, james Hutton is often viewed as the first modern geologist. In 1785 he presented a paper entitled Theory of the Earth to the Royal Society of Edinburgh, Hutton published a two-volume version of his ideas in 1795. The first geological map of the U. S. was produced in 1809 by William Maclure, in 1807, Maclure commenced the self-imposed task of making a geological survey of the United States. Almost every state in the Union was traversed and mapped by him and this antedates William Smiths geological map of England by six years, although it was constructed using a different classification of rocks. Sir Charles Lyell first published his famous book, Principles of Geology and this book, which influenced the thought of Charles Darwin, successfully promoted the doctrine of uniformitarianism. This theory states that slow geological processes have occurred throughout the Earths history and are still occurring today, in contrast, catastrophism is the theory that Earths features formed in single, catastrophic events and remained unchanged thereafter. Though Hutton believed in uniformitarianism, the idea was not widely accepted at the time, most geologists also need skills in GIS and other mapping techniques. Geology students often spend portions of the year, especially the summer though sometimes during a January term, geologists may concentrate their studies or research in one or more of the following disciplines, Dendrochronology, the study of dating based on tree ring patterns. Economic geology, the study of ore genesis, and the mechanisms of ore creation, geochemistry, the applied branch deals with the study of the chemical makeup and behaviour of rocks, and the study of the behaviour of their minerals. Geochronology, the study of isotope geology specifically toward determining the date within the past of rock formation, metamorphism, mineralization and geological events. Geomorphology, the study of landforms and the processes that create them Hydrogeology, igneous petrology, the study of igneous processes such as igneous differentiation, fractional crystallization, intrusive and volcanological phenomena. Isotope geology, the case of the composition of rocks to determine the processes of rock. Metamorphic petrology, the study of the effects of metamorphism on minerals, marine geology, the study of the seafloor, involves geophysical, geochemical, sedimentological and paleontological investigations of the ocean floor and coastal margins. Marine geology has strong ties to physical oceanography and plate tectonics, palaeoclimatology, the application of geological science to determine the climatic conditions present in the Earths atmosphere within the Earths history
Geologist
–
"The Geologist" -
Carl Spitzweg, circa 1860
Geologist
–
Scotsman James Hutton, father of modern geology
Geologist
–
"Geologists at work" from the U.S. Geological and Geographic Survey of the Territories. (1874 - 06/30/1879) Photographer:
William Henry Jackson
Geologist
–
A young geologist learns about
flow banding
12.
Preston Cloud
–
Preston Ercelle Cloud, Jr. was an eminent American earth scientist, biogeologist, cosmologist, and paleontologist. He served in the United States Navy, and led several explorations of the U. S. Geological Survey. In academia, he was member of faculty of Harvard University, University of Minnesota, University of California, Los Angeles and he was best known for his work on the geologic time scale and the origin of life on Earth, and as a pioneering ecologist and environmentalist. He was credited with coining the term biogeology and his works on the significance of Cambrian fossils in the 1940s led to the development of the concept Cambrian explosion, for which he coined the phrase eruptive evolution. Cloud was born in West Upton, Massachusetts and he was the third of seven children of Preston Ercelle and Pauline L. Cloud. His father was an engineer-draftsman, and his mother, a genealogist and he grew up in Waynesboro, Pennsylvania where he developed a love for the outdoors. He enjoyed Scouting and was an Eagle Scout, upon graduating from Waynesboro High School in 1929, Cloud spent three years in the United States Navy where he excelled at boxing. He was the champion of the Pacific Fleet Scouting Force. Due to the Great Depression, he could not join university, ray S. Bassler, his geology professor and Curator of Geology at the U. S. National Museum, helped him to get manual jobs in the museum. Because of his keen interest in paleontology, he was given a job as a preparator in the laboratory under G. Arthur Cooper. It was Cooper who guided him to have his first technical publication on Devonian brachiopods from Illinois in 1938, in 1937 he earned his BSc degree, and was elected to Phi Beta Kappa. He enrolled for PhD at Yale University graduate school in geology the same year, working on the major systematic monograph on a group of Paleozoic brachiopods, under the supervision of C. O. Dunbar, he received his doctorate in 1940. His thesis directly earned him the A. Cressey Morrison Prize in Natural History of the New York Academy of Sciences, in the summer of 1939, Cloud worked as field assistant to A. Lincoln Washburn on Victoria Island in western Arctic Canada. For the rest of the year he taught at the Missouri School of Mines in Rolla, during 1941 to 1942 he returned to Yale University to continue work on brachiopod evolution as a Sterling Research Fellow. At the height of World War II, he was recruited to the United States Geological Survey to work on the wartime Strategic Minerals Program and he embarked on a field party to investigate manganese deposits in Maine during the summer of 1941. In 1943, he joined Virgil Barnes of the Texas Bureau of Economic Geology in the Ellenburger Project, studying the stratigraphy and he became chief of party for bauxite investigations in Alabama. After the war, in 1946, Cloud was appointed as Assistant Professor of Paleontology, in 1948 he returned to the U. S. Geological Survey to become chief of the Branch of Paleontology and Stratigraphy. He was chief of party to map and investigate the geology of Saipan in the Mariana Islands in the western Pacific and he became Chief Paleontologist from 1949 to 1959
Preston Cloud
–
Preston Cloud
13.
Rock (geology)
–
Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a rock, is a combination of the minerals quartz, feldspar. The Earths outer solid layer, the lithosphere, is made of rock, rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization, three major groups of rocks are defined, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is a component of geology. At a granular level, rocks are composed of grains of minerals, the aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed, many rocks contain silica, a compound of silicon and oxygen that forms 74. 3% of the Earths crust. This material forms crystals with other compounds in the rock, the proportion of silica in rocks and minerals is a major factor in determining their name and properties. Rocks are geologically classified according to such as mineral and chemical composition, permeability, the texture of the constituent particles. These physical properties are the end result of the processes that formed the rocks, over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock, igneous, sedimentary, and metamorphic, the three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks, hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. Igneous rock forms through the cooling and solidification of magma or lava and this magma can be derived from partial melts of pre-existing rocks in either a planets mantle or crust. Typically, the melting of rocks is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, igneous rocks are divided into two main categories, plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust, a common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, the chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowens reaction series. Most major igneous rocks are found along this scale, about 64. 7% of the Earths crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, only 0. 6% are syenites and 0. 3% peridotites and dunites
Rock (geology)
–
Balanced Rock stands in the
Garden of the Gods park in
Colorado Springs
Rock (geology)
–
Rock outcrop along a mountain creek near
Orosí,
Costa Rica.
Rock (geology)
–
Sample of igneous
gabbro
Rock (geology)
–
Sedimentary sandstone with iron oxide bands
14.
Timeline of the evolutionary history of life
–
This timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth. In biology, evolution is any change across generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of organization, from kingdoms to species. The similarities between all present day organisms indicate the presence of an ancestor from which all known species, living. More than 99 percent of all species, amounting to five billion species. Estimates on the number of Earths current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. Species go extinct constantly as environments change, organisms compete for environmental niches, occasionally biodiversity on the planet takes a hit in the form of a mass extinction in which the extinction rate is much higher than usual. A large extinction event often represents an accumulation of smaller extinction events that take place in a brief period of time. The first known mass extinction in earths history was the Great Oxygenation Event 2.4 billion years ago, the event led to the loss of most of the planets obligate anaerobes. The Holocene extinction event is currently under way, in this timeline, Ma means million years ago, ka means thousand years ago, and ya means years ago. 4000 Ma –2500 Ma 2500 Ma –542 Ma, contains the Palaeoproterozoic, Mesoproterozoic and Neoproterozoic eras. 542 Ma – present The Phanerozoic Eon, literally the period of well-displayed life, marks the appearance in the record of abundant. It is subdivided into three eras, the Paleozoic, Mesozoic and Cenozoic, which are divided by mass extinctions. 542 Ma –251.0 Ma and contains the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, from 251.4 Ma to 66 Ma and containing the Triassic, Jurassic and Cretaceous periods. 66 Ma – present Dawkins, Richard, the Ancestors Tale, A Pilgrimage to the Dawn of Life. Understanding Evolution, your one-stop resource for information on evolution, explore complete phylogenetic tree interactively Brandt, Niel. Houston, TX, The TalkOrigins Foundation, Inc, interactive timeline from Big Bang to present Plant Evolution. Sequence of Plant Evolution The History of Animal Evolution, sequence of Animal Evolution Yeo, Dannel, Drage, Thomas
Timeline of the evolutionary history of life
–
Moon
Timeline of the evolutionary history of life
–
Visual representation of the history of life on Earth as a spiral.
Timeline of the evolutionary history of life
–
Fragment of the
Acasta Gneiss exhibited at the
Museum of Natural History in Vienna.
Timeline of the evolutionary history of life
–
The
cyanobacterial -algal mat, salty lake on the
White Sea seaside
15.
Water
–
Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
Water
–
Water in three states: liquid, solid (
ice), and gas (invisible
water vapor in the air).
Clouds are accumulations of water droplets,
condensed from vapor-saturated air.
Water
–
Impact from a water drop causes an upward "rebound" jet surrounded by circular
capillary waves.
Water
–
Snowflakes by
Wilson Bentley, 1902.
Water
–
Dew drops adhering to a
spider web.
16.
Unicellular organism
–
A unicellular organism, also known as a single-celled organism, is an organism that consists of only one cell, unlike a multicellular organism that consists of more than one cell. Historically, simple unicellular organisms have been referred to as monads, though this term is used more specifically to describe organisms of the genus Monas. The main groups of organisms are bacteria, archaea, protozoa, unicellular algae. Unicellular organisms fall into two categories, prokaryotic organisms and eukaryotic organisms. Unicellular organisms are thought to be the oldest form of life, prokaryotes, most Protista, and some fungi are unicellular. Although some of these live in colonies, they dont exhibit specialization. These organisms live together, and each cell in the colony is the same, however, each individual cell must carry out all life processes to survive. In contrast, even the simplest multicellular organisms have cells that depend on each other to survive, most multicellular organisms have a unicellular life-cycle stage. Gametes, for example, are reproductive unicells for multicellular organisms, additionally, multicellularity appears to have evolved independently many times in the history of life. Some organisms are partially uni- and multicellular, like Dictyostelium discoideum, additionally, unicellular organisms can be multinucleate, like Myxogastria and Plasmodium. Candidatus Magnetoglobus multicellular, related to Deltaproteobacteria, is a multicellular prokaryote and it is neither unicellular, nor a colony. Primitive cells, often referred to as protocells, are the precursors to todays unicellular organisms, the RNA world hypothesis assumes that RNA molecules could form in abiotic conditions, which would require nucleic acids and ribose to be present. Theoretical and experimental findings show that nucleic acids and sugars could have been synthesized in early prebiotic conditions, compartmentalization was necessary for chemical reactions to be more likely as well as to differentiate reactions with the external environment. For example, an early RNA replicator ribozyme may have replicated other replicator ribozymes of different RNA sequences if not kept separate, when amphiphiles like lipids are placed in water, the hydrophobic tails aggregate to form micelles and vesicles, with the hydrophilic ends facing outwards. Primitive cells likely used self-assembling fatty-acid vesicles to separate chemical reactions, because of their simplicity and ability to self-assemble in water, its likely that these simple membranes predated other forms of early biological molecules. Prokaryotes lack membrane-bound organelles, such as mitochondria or a nucleus, instead, most prokaryotes have an irregular region that contains DNA, known as the nucleoid. Most prokaryotes have a single, circular chromosome, which is in contrast to eukaryotes, nutritionally, prokaryotes have the ability to utilize a wide range of organic and inorganic material for use in metabolism, including sulfur, cellulose, ammonia, or nitrite. Prokaryotes as a whole are ubiquitous in the environment and exist in extreme environments as well, bacteria are one of the world’s oldest forms of life, and are found virtually everywhere in nature
Unicellular organism
–
Valonia ventricosa, a species of
algae with a diameter that ranges typically from 1 to 4 centimetres (0.39 to 1.57 in) is among the largest unicellular species
17.
Evolution of photosynthesis
–
The first photosynthetic organisms probably evolved early in the evolutionary history of life and most likely used reducing agents such as hydrogen or electrons, rather than water. There are three major metabolic pathways by which photosynthesis is carried out, C3 photosynthesis, C4 photosynthesis, C3 photosynthesis is the oldest and most common form. The biochemical capacity to use water as the source for electrons in photosynthesis evolved in an ancestor of extant cyanobacteria. The geological record indicates that this event took place early in Earths history, at least 2450–2320 million years ago. Available evidence from studies of Archean sedimentary rocks indicates that life existed 3500 Ma. A clear paleontological window on cyanobacterial evolution opened about 2000 Ma, cyanobacteria remained principal primary producers throughout the Proterozoic Eon, in part because the redox structure of the oceans favored photoautotrophs capable of nitrogen fixation. Cyanobacteria remain critical to marine ecosystems as primary producers in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae. Early photosynthetic systems, such as those from green and purple sulfur and green and purple bacteria, are thought to have been anoxygenic. Green and purple sulfur bacteria are thought to have used hydrogen, green nonsulfur bacteria used various amino and other organic acids. Purple nonsulfur bacteria used a variety of organic molecules. Fossils of what are thought to be filamentous photosynthetic organisms have been dated at 3.4 billion years old, the main source of oxygen in the atmosphere is oxygenic photosynthesis, and its first appearance is sometimes referred to as the oxygen catastrophe. Geological evidence suggests that oxygenic photosynthesis, such as that in cyanobacteria, modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic. Oxygenic photosynthesis uses water as a donor, which is oxidized to molecular oxygen in the photosynthetic reaction center. Several groups of animals have formed relationships with photosynthetic algae. These are most common in corals, sponges and sea anemones and it is presumed that this is due to the particularly simple body plans and large surface areas of these animals compared to their volumes. This allows the mollusks to survive solely by photosynthesis for several months at a time, some of the genes from the plant cell nucleus have even been transferred to the slugs, so that the chloroplasts can be supplied with proteins that they need to survive. An even closer form of symbiosis may explain the origin of chloroplasts, chloroplasts have many similarities with photosynthetic bacteria, including a circular chromosome, prokaryotic-type ribosomes, and similar proteins in the photosynthetic reaction center. The endosymbiotic theory suggests that bacteria were acquired by early eukaryotic cells to form the first plant cells
Evolution of photosynthesis
–
Plant cells with visible chloroplasts (from a moss,
Plagiomnium affine)
Evolution of photosynthesis
–
CAM is named after the family
Crassulaceae, to which the
jade plant belongs. Another example of a CAM plant is the
pineapple.
18.
Eukaryote
–
A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes. Eukaryotes belong to the taxon Eukarya or Eukaryota, the presence of a nucleus gives eukaryotes their name, which comes from the Greek εὖ and κάρυον. Eukaryotic cells also contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, in addition, plants and algae contain chloroplasts. Eukaryotic organisms may be unicellular or multicellular, only eukaryotes form multicellular organisms consisting of many kinds of tissue made up of different cell types. Eukaryotes can reproduce asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two identical cells. In meiosis, DNA replication is followed by two rounds of division to produce four daughter cells each with half the number of chromosomes as the original parent cell. These act as sex cells resulting from genetic recombination during meiosis, the domain Eukaryota appears to be monophyletic, and so makes up one of the three domains of life. The two other domains, Bacteria and Archaea, are prokaryotes and have none of the above features, eukaryotes represent a tiny minority of all living things. However, due to their larger size, eukaryotes collective worldwide biomass is estimated at about equal to that of prokaryotes. Eukaryotes first developed approximately 1. 6–2.1 billion years ago, in 1905 and 1910, the Russian biologist Konstantin Mereschkowsky argued three things about the origin of nucleated cells. Firstly, plastids were reduced cyanobacteria in a symbiosis with a non-photosynthetic host, secondly, the host had earlier in evolution formed by symbiosis between an amoeba-like host and a bacteria-like cell that formed the nucleus. Thirdly, plants inherited photosynthesis from cyanobacteria, the split between the prokaryotes and eukaryotes was introduced in the 1960s. The concept of the eukaryote has been attributed to the French biologist Edouard Chatton, the terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C. B. van Niel in 1962. In his 1938 work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes. However he mentioned this in one paragraph, and the idea was effectively ignored until Chattons statement was rediscovered by Stanier. In 1967, Lynn Margulis provided microbiological evidence for endosymbiosis as the origin of chloroplasts and mitochondria in cells in her paper. In the 1970s, Carl Woese explored microbial phylogenetics, studying variations in 16S ribosomal RNA and this helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organelles, mitochondria and chloroplasts
Eukaryote
–
Had'n
Eukaryote
–
Longitudinal section through the flagellum of
Chlamydomonas reinhardtii
19.
Multicellular organism
–
Multicellular organisms are organisms that consist of more than one cell, in contrast to unicellular organisms. Multicellular organisms arise in different ways, for example by cell division or by aggregation of many single cells. Colonial organisms are the result of identical individuals joining together to form a colony. Multicellularity has evolved independently at least 46 times, including in some prokaryotes, like cyanobacteria, myxobacteria, actinomycetes, however, complex multicellular organisms evolved only in six eukaryotic groups, animals, fungi, brown algae, red algae, green algae, and land plants. It evolved repeatedly for Chloroplastida, once or twice for animals, once for brown algae, the first evidence of multicellularity is from cyanobacteria-like organisms that lived 3–3.5 billion years ago. To reproduce, true multicellular organisms must solve the problem of regenerating a whole organism from germ cells, animals have evolved a considerable diversity of cell types in a multicellular body, compared with 10–20 in plants and fungi. Loss of multicellularity occurred in some groups, fungi are predominantly multicellular, though early diverging lineages are largely unicellular and there have been numerous reversions to unicellularity across fungi. It may also have occurred in some red algae, but it is possible that they are primitively unicellular), loss of multicellularity is also considered probable in some green algae. In other groups, generally parasites, a reduction of multicellularity occurred, multicellular organisms, especially long-living animals, face the challenge of cancer, which occurs when cells fail to regulate their growth within the normal program of development. Changes in tissue morphology can be observed during this process, cancer in animals has often been described as a loss of multicellularity. There is a discussion about the possibility of existence of cancer in other organisms or even in protozoa. For example, plant galls have been characterized as tumors but some argue that plants do not develop cancer. In some multicellular groups, which are called Weismannists, a separation between a sterile somatic cell line and a cell line evolved. However, Weismannist development is relatively rare, as part of species have the capacity for somatic embryogenesis. One hypothesis for the origin of multicellularity is that a group of function-specific cells aggregated into a mass called a grex. This is essentially what slime molds do, another hypothesis is that a primitive cell underwent nucleus division, thereby becoming a coenocyte. A membrane would then form around each nucleus, thereby resulting in a group of connected cells in one organism and this is what plant and animal embryos do as well as colonial choanoflagellates. Because the first multicellular organisms were simple, soft organisms lacking bone, shell or other body parts
Multicellular organism
–
In this image, a
wild-type Caenorhabditis elegans is stained to highlight the nuclei of its cells.
Multicellular organism
20.
Silurian
–
The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago, to the beginning of the Devonian Period,419.2 Mya. As with other periods, the rock beds that define the periods start and end are well identified. The base of the Silurian is set at a major Ordovician-Silurian extinction event when 60% of marine species were wiped out, a significant evolutionary milestone during the Silurian was the diversification of jawed and bony fish. However, terrestrial life would not greatly diversify and affect the landscape until the Devonian, the Silurian system was first identified by British geologist Sir Roderick Impey Murchison, who was examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s. He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick and this naming does not indicate any correlation between the occurrence of the Silurian rocks and the land inhabited by the Silures. As it was first identified, the Silurian series when traced farther afield quickly came to overlap Sedgwicks Cambrian sequence, however, charles Lapworth resolved the conflict by defining a new Ordovician system including the contested beds. An early alternative name for the Silurian was Gotlandian after the strata of the Baltic island of Gotland, the French geologist Joachim Barrande, building on Murchisons work, used the term Silurian in a more comprehensive sense than was justified by subsequent knowledge. He divided the Silurian rocks of Bohemia into eight stages and his interpretation was questioned in 1854 by Edward Forbes, and the later stages of Barrande, F, G and H, have since been shown to be Devonian. Despite these modifications in the groupings of the strata, it is recognized that Barrande established Bohemia as a classic ground for the study of the earliest fossils. The epoch is named for the town of Llandovery in Carmarthenshire, the Wenlock, which lasted from 433.4 ±1.5 to 427.4 ±2.8 mya, is subdivided into the Sheinwoodian and Homerian ages. It is named after Wenlock Edge in Shropshire, England, during the Wenlock, the oldest known tracheophytes of the genus Cooksonia, appear. The first terrestrial animals also appear in the Wenlock, represented by air-breathing millipedes from Scotland. The Ludlow, lasting from 427.4 ±1.5 to 423 ±2.8 mya, comprises the Gorstian stage, lasting until 425.6 million years ago, and it is named for the town of Ludlow in Shropshire, England. The Pridoli, lasting from 423 ±1.5 to 419.2 ±2.8 mya, is the final and it is named after one locality at the Homolka a Přídolí nature reserve near the Prague suburb Slivenec in the Czech Republic. Přídolí is the old name of a field area. The high sea levels of the Silurian and the flat land resulted in a number of island chains. The southern continents remained united during this period, the melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity. The continents of Avalonia, Baltica, and Laurentia drifted together near the equator and this event is the Caledonian orogeny, a spate of mountain building that stretched from New York State through conjoined Europe and Greenland to Norway
Silurian
–
Ordovician -Silurian boundary on
Hovedøya,
Norway, showing gray Ordovician
sandstone and brown Silurian
mudstone. The layers have been overturned by the
Caledonian orogeny.
Silurian
–
Marine extinction intensity during the
Phanerozoic
Silurian
–
Silurian sea bed fossils collected from Wren's Nest Nature Reserve, Dudley UK
Silurian
–
Crinoid fragments in a Silurian (Pridoli) limestone (
Saaremaa, Estonia)
21.
Dinosaur
–
Dinosaurs are a diverse group of reptiles of the clade Dinosauria that first appeared during the Triassic. Although the exact origin and timing of the evolution of dinosaurs is the subject of active research and they became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago. Their dominance continued through the Jurassic and Cretaceous periods and ended when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur groups 66 million years ago, until the late 20th century, all groups of dinosaurs were believed to be extinct. As such, birds were the dinosaur lineage to survive the mass extinction event. This article deals primarily with non-avian dinosaurs, Dinosaurs are a varied group of animals from taxonomic, morphological and ecological standpoints. Birds, at over 10,000 living species, are the most diverse group of vertebrates besides perciform fish, using fossil evidence, paleontologists have identified over 500 distinct genera and more than 1,000 different species of non-avian dinosaurs. Dinosaurs are represented on every continent by both extant species and fossil remains, while dinosaurs were ancestrally bipedal, many extinct groups included quadrupedal species, and some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, evidence suggests that egg laying and nest building are additional traits shared by all dinosaurs.7 meters and heights of 18 meters and were the largest land animals of all time. Still, the idea that dinosaurs were uniformly gigantic is a misconception based in part on preservation bias, as large. Many dinosaurs were small, Xixianykus, for example, was only about 50 cm long. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the community believed dinosaurs to have been sluggish. Most research conducted since the 1970s, however, has indicated that all dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction. The large sizes of some groups, as well as their seemingly monstrous and fantastic nature, have ensured dinosaurs regular appearance in best-selling books and films. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, the term is derived from the Greek words δεινός and σαῦρος. Though the taxonomic name has often interpreted as a reference to dinosaurs teeth, claws. Instead, dinosaurs, like many forms of reptile sub-groups, did not exhibit characteristics which were traditionally regarded as reptilian. Under phylogenetic nomenclature, dinosaurs are usually defined as the group consisting of Triceratops, Neornithes, their most recent common ancestor, Birds are now recognized as being the sole surviving lineage of theropod dinosaurs. In traditional taxonomy, birds were considered a class that had evolved from dinosaurs
Dinosaur
Dinosaur
–
The world's smallest dinosaur footprint, the Hunterian Museum, Glasgow.
Dinosaur
–
Triceratops horridus skeleton,
Natural History Museum of Los Angeles County
Dinosaur
–
The common
house sparrow (Passer domesticus) is often used to represent modern birds in definitions of the group Dinosauria.
22.
Mammal
–
Mammals are any vertebrates within the class Mammalia, a clade of endothermic amniotes distinguished from reptiles by the possession of a neocortex, hair, three middle ear bones and mammary glands. All female mammals nurse their young with milk, secreted from the mammary glands, Mammals include the largest animals on the planet, the great whales. The basic body type is a quadruped, but some mammals are adapted for life at sea, in the air, in trees. The largest group of mammals, the placentals, have a placenta, Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale. With the exception of the five species of monotreme, all modern mammals give birth to live young, most mammals, including the six most species-rich orders, belong to the placental group. The largest orders are the rodents, bats and Soricomorpha, the next three biggest orders, depending on the biological classification scheme used, are the Primates, the Cetartiodactyla, and the Carnivora. Living mammals are divided into the Yinotheria and Theriiformes There are around 5450 species of mammal, in some classifications, extant mammals are divided into two subclasses, the Prototheria, that is, the order Monotremata, and the Theria, or the infraclasses Metatheria and Eutheria. The marsupials constitute the group of the Metatheria, and include all living metatherians as well as many extinct ones. Much of the changes reflect the advances of cladistic analysis and molecular genetics, findings from molecular genetics, for example, have prompted adopting new groups, such as the Afrotheria, and abandoning traditional groups, such as the Insectivora. The mammals represent the only living Synapsida, which together with the Sauropsida form the Amniota clade, the early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period, this group diverged from the line that led to todays reptiles. Some mammals are intelligent, with some possessing large brains, self-awareness, Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals, singing, and echolocation. Mammals can organize themselves into fission-fusion societies, harems, and hierarchies, most mammals are polygynous, but some can be monogamous or polyandrous. They provided, and continue to provide, power for transport and agriculture, as well as commodities such as meat, dairy products, wool. Mammals are hunted or raced for sport, and are used as model organisms in science, Mammals have been depicted in art since Palaeolithic times, and appear in literature, film, mythology, and religion. Defaunation of mammals is primarily driven by anthropogenic factors, such as poaching and habitat destruction, Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is accepted, McKenna & Bell and Wilson & Reader provide useful recent compendiums. Though field work gradually made Simpsons classification outdated, it remains the closest thing to a classification of mammals
Mammal
–
Goat kids will stay with their mother until they are weaned.
Mammal
23.
Flowering plant
–
The flowering plants, also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants, with 416 families, approx. 13,164 known genera and a total of c.295,383 known species, etymologically, angiosperm means a plant that produces seeds within an enclosure, in other words, a fruiting plant. The term angiosperm comes from the Greek composite word meaning enclosed seeds, the ancestors of flowering plants diverged from gymnosperms in the Triassic Period, during the range 245 to 202 million years ago, and the first flowering plants are known from 160 mya. They diversified extensively during the Lower Cretaceous, became widespread by 120 mya, angiosperms differ from other seed plants in several ways, described in the table. These distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants, the amount and complexity of tissue-formation in flowering plants exceeds that of gymnosperms. The vascular bundles of the stem are arranged such that the xylem and phloem form concentric rings, in the dicotyledons, the bundles in the very young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium, the soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Among the monocotyledons, the bundles are more numerous in the stem and are scattered through the ground tissue. They contain no cambium and once formed the stem increases in diameter only in exceptional cases, the characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, and provide the most trustworthy external characteristics for establishing relationships among angiosperm species, the function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds. The floral apparatus may arise terminally on a shoot or from the axil of a leaf, occasionally, as in violets, a flower arises singly in the axil of an ordinary foliage-leaf. There are two kinds of cells produced by flowers. Microspores, which divide to become pollen grains, are the male cells and are borne in the stamens. The female cells called megaspores, which divide to become the egg cell, are contained in the ovule. The flower may consist only of parts, as in willow. Usually, other structures are present and serve to protect the sporophylls, the individual members of these surrounding structures are known as sepals and petals. The outer series is usually green and leaf-like, and functions to protect the rest of the flower, the inner series is, in general, white or brightly colored, and is more delicate in structure. It functions to attract insect or bird pollinators, attraction is effected by color, scent, and nectar, which may be secreted in some part of the flower
Flowering plant
Flowering plant
–
Bud of a pink
rose
Flowering plant
–
Flowers of
Malus sylvestris (crab apple)
Flowering plant
–
Flowers and leaves of
Oxalis pes-caprae (Bermuda buttercup)
24.
History of Earth
–
The history of Earth concerns the development of the planet Earth from its formation to the present day. Nearly all branches of science have contributed to the understanding of the main events of the Earths past. The age of Earth is approximately one-third of the age of the universe, an immense amount of geological change has occurred in that timespan, accompanied by the emergence of life and its subsequent evolution. Earth formed around 4.54 billion years ago by accretion from the solar nebula, volcanic outgassing probably created the primordial atmosphere and then the ocean, but the atmosphere contained almost no oxygen and so would have been toxic to most modern life including humans. Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism. A giant impact collision with a body named Theia while Earth was in its earliest stage. Over time, the Earth cooled, causing the formation of a solid crust, the geological time scale clock depicts the larger spans of time from the beginning of the Earth as well as a chronology of some definitive events of Earth history. The Archean and Proterozoic eons follow, they produced the abiogenesis of life on Earth, there are microbial mat fossils such as stromatolites found in 3.48 billion-year-old sandstone discovered in Western Australia. According to one of the researchers, If life arose relatively quickly on Earth … then it could be common in the universe, living forms derived from photosynthesis appeared between 3.2 and 2.4 billion years ago and began enriching the atmosphere with oxygen. More than 99 percent of all species, amounting to five billion species. Estimates on the number of Earths current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described. Geological change has been a constant of Earths crust since the time of its formation, species continue to evolve, taking on new forms, splitting into daughter species or going extinct in the process of adapting or dying in response to ever-changing physical environments. The process of plate tectonics continues to play a dominant role in the shaping of Earths oceans and continents, in geochronology, time is generally measured in mya, each unit representing the period of approximately 1,000,000 years in the past. The history of Earth is divided into four great eons, starting 4,540 mya with the formation of the planet, each eon saw the most significant changes in Earths composition, climate and life. Each eon is divided into eras, which in turn are divided into periods. The history of the Earth can be organized according to the geologic time scale. The following four timelines show the time scale
History of Earth
–
Artistic concept of the primordial Earth when it was much hotter and hostile to life
History of Earth
–
An artist's rendering of a
protoplanetary disk
History of Earth
–
Geologic map of North America, color-coded by age. The reds and pinks indicate rock from the
Archean.
History of Earth
–
Lithified stromatolites on the shores of
Lake Thetis,
Western Australia. Archean stromatolites are the first direct fossil traces of life on Earth.
25.
Age of the Earth
–
The age of the Earth is 4.54 ±0.05 billion years. This dating is based on evidence from radiometric age-dating of meteorite material and is consistent with the ages of the oldest-known terrestrial. Following the development of radiometric age-dating in the early 20th century, the oldest such minerals analyzed to date—small crystals of zircon from the Jack Hills of Western Australia—are at least 4.404 billion years old. Comparing the mass and luminosity of the Sun to those of other stars and it is hypothesised that the accretion of Earth began soon after the formation of the calcium-aluminium-rich inclusions and the meteorites. It is also difficult to determine the age of the oldest rocks on Earth, exposed at the surface. Studies of strata, the layering of rocks and earth, gave naturalists an appreciation that Earth may have been many changes during its existence. These layers often contained fossilized remains of creatures, leading some to interpret a progression of organisms from layer to layer. Nicolas Steno in the 17th century was one of the first naturalists to appreciate the connection between fossil remains and strata and his observations led him to formulate important stratigraphic concepts. In the 1790s, William Smith hypothesized that if two layers of rock at widely differing locations contained similar fossils, then it was plausible that the layers were the same age. William Smiths nephew and student, John Phillips, later calculated by means that Earth was about 96 million years old. In the mid-18th century, the naturalist Mikhail Lomonosov suggested that Earth had been created separately from, and several hundred years before. In 1779 the Comte du Buffon tried to obtain a value for the age of Earth using an experiment, He created a globe that resembled Earth in composition. This led him to estimate that Earth was about 75,000 years old, other naturalists used these hypotheses to construct a history of Earth, though their timelines were inexact as they did not know how long it took to lay down stratigraphic layers. This was a challenge to the view, which saw the history of Earth as static. Many naturalists were influenced by Lyell to become uniformitarians who believed that changes were constant, in 1862, the physicist William Thomson, 1st Baron Kelvin published calculations that fixed the age of Earth at between 20 million and 400 million years. He assumed that Earth had formed as a completely molten object, geologists such as Charles Lyell had trouble accepting such a short age for Earth. For biologists, even 100 million years seemed much too short to be plausible, in Darwins theory of evolution, the process of random heritable variation with cumulative selection requires great durations of time. In a lecture in 1869, Darwins great advocate, Thomas H. Huxley, attacked Thomsons calculations and their values were consistent with Thomsons calculations
Age of the Earth
–
Earth as seen from
Apollo 17
Age of the Earth
–
William Thomson (Lord Kelvin)
Age of the Earth
–
Ernest Rutherford in 1908.
Age of the Earth
–
Fragment of the Canyon Diablo iron meteorite.
26.
Origin of water on Earth
–
The origin of water on Earth, or the reason that there is clearly more liquid water on Earth than on the other rocky planets of the Solar System, is not completely understood. There exist numerous more or less mutually compatible hypotheses as to how water may have accumulated on Earths surface over the past 4.5 billion years in sufficient quantity to form oceans. Comets, trans-Neptunian objects or water-rich meteoroids from the reaches of the asteroid belt colliding with Earth may have brought water to the worlds oceans. Large enough Planetesimals were heated by the decay of aluminium isotope and this could cause water to rise to the surface. What is however unclear is whether these comets are representative of those from the Kuiper Belt, the water in carbon-rich chondrites point to a similar D/H ratio as oceanic water. Nevertheless, mechanisms have been proposed to suggest that the D/H-ratio of oceanic water may have increased significantly throughout Earths history, such a proposal is consistent with the possibility that a significant amount of the water on Earth was already present during the planets early evolution. Recent measurements of the composition of Moon rocks suggest that Earth was born with its water already present. Investigating lunar samples carried to Earth by the Apollo 15 and 17 missions found a ratio that matched the isotopic ratio in carbonaceous chondrites. The ratio is similar to that found in water on Earth. The findings suggest a common source of water for both objects and this supports a theory that Jupiter temporarily migrated into the inner Solar System, destabilizing the orbits of water-rich carbonaceous chondrites. As a result, some of the bodies could have fallen inwards and become part of the raw material for making Earth, the discovery of water vapor out-gassing from Ceres provides related information on water-ice content of the asteroid belt. Gradual leakage of stored in hydrate minerals of Earths rocks could have formed a portion of its water. Water may also have come from volcanism, water vapor in the atmosphere that originated in volcanic eruptions may have condensed to form rain, a sizeable quantity of water would have been in the material that formed Earth. Water molecules would have escaped Earths gravity more easily when it was less massive during its formation, part of the young planet is theorized to have been disrupted by the impact which created the Moon, which should have caused melting of one or two large areas. Present composition does not match complete melting and it is hard to melt, however, a fair fraction of material should have been vaporized by this impact, creating a rock-vapor atmosphere around the young planet. The rock-vapor would have condensed within two years, leaving behind hot volatiles which probably resulted in a heavy carbon dioxide atmosphere with hydrogen. Liquid water oceans existed despite the temperature of 230°C because of the atmospheric pressure of the heavy CO2 atmosphere. As cooling continued, subduction and dissolving in ocean water removed most CO2 from the atmosphere but levels oscillated wildly as new surface and mantle cycles appeared
Origin of water on Earth
–
Water covers about 75% of the Earth's surface
27.
Late Heavy Bombardment
–
The Late Heavy Bombardment is an event thought to have occurred approximately 4.1 to 3.8 billion years ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. The LHB happened after the Earth and other rocky planets had formed and accreted most of their mass, Evidence for the LHB derives from lunar samples brought back by the Apollo astronauts. Isotopic dating of Moon rocks implies that most impact melts occurred in a narrow interval of time. Several hypotheses attempt to explain the apparent spike in the flux of impactors in the inner Solar System and they also note that the rate of impact cratering could differ significantly between the outer and inner zones of the Solar System. The main piece of evidence for a lunar cataclysm comes from the ages of impact melt rocks that were collected during the Apollo missions. The majority of impact melts are believed to have formed during the collision of asteroids or comets tens of kilometers across. The Apollo 15,16, and 17 landing sites were chosen as a result of their proximity to the Imbrium, Nectaris, under study on Earth, the ages of impact melts collected at these sites clustered between about 3.8 and 4.1 Ga. The apparent clustering of ages of these led to postulation that the record an intense bombardment of the Moon. They called it the lunar cataclysm and proposed that it represented an increase in the rate of bombardment of the Moon around 3.9 Ga. At the time, the conclusion was considered controversial, as more data has become available, particularly from lunar meteorites, this theory, while still controversial, has gained in popularity. The lunar meteorites are believed to randomly sample the lunar surface, many of the feldspathic lunar meteorites probably originated from the lunar far side, and impact melts within these have recently been dated. Consistent with the hypothesis, none of their ages was found to be older than about 3.9 Ga. Nevertheless, the ages do not cluster at this date. Dating of howardite, eucrite and diogenite meteorites and H chondrite meteorites originating from the asteroid belt reveal numerous ages from 3. 4–4.1 Ga, impact velocities above 10 km/s require very high inclinations or the large eccentricities of asteroids on planet crossing orbits. Such objects are rare in the current asteroid belt but the population would be increased by the sweeping of resonances due to giant planet migration. Studies of the highland crater size distributions suggest that the family of projectiles struck Mercury. The first criticism concerns the origin of the impact melt rocks that were sampled at the Apollo landing sites. While these impact melts have been attributed to having been derived from the closest basin. According to this hypothesis, the cluster of impact melt ages near 3.9 Ga simply reflects material being collected from a single impact event, Imbrium
Late Heavy Bombardment
–
Artist's impression of the moon during the Late Heavy Bombardment (Lunar Cataclysm) and today
Late Heavy Bombardment
–
Physical lunar features
Late Heavy Bombardment
–
Lists
28.
Geological history of oxygen
–
Before photosynthesis evolved, Earths atmosphere had no free oxygen. Photosynthetic prokaryotic organisms that produced O2 as a waste product lived long before the first build-up of free oxygen in the atmosphere, the oxygen they produced would have been rapidly removed from the atmosphere by weathering of reducing minerals, most notably iron. This mass rusting led to the deposition of oxide on the ocean floor. Oxygen only began to persist in the atmosphere in small quantities about 50 million years before the start of the Great Oxygenation Event and this mass oxygenation of the atmosphere resulted in rapid buildup of free oxygen. At current rates of production, todays concentration of oxygen could be produced by photosynthetic organisms in 2,000 years.9 billion years ago. The presence of O2 provided life with new opportunities, aerobic metabolism is more efficient than anaerobic pathways, and the presence of oxygen undoubtedly created new possibilities for life to explore. Since the start of the Cambrian period, atmospheric oxygen concentrations have fluctuated between 15% and 35% of atmospheric volume. The maximum of 35% was reached towards the end of the Carboniferous period, whilst human activities, such as the burning of fossil fuels, affect relative carbon dioxide concentrations, their effect on the much larger concentration of oxygen is less significant. But Haldanes essay points out that it would apply to insects. However, the basis for this correlation is not firm. There is no significant correlation between atmospheric oxygen and maximum body size elsewhere in the geological record, ecological constraints can better explain the diminutive size of post-Carboniferous dragonflies - for instance, the appearance of flying competitors such as pterosaurs, birds and bats. The most celebrated link between oxygen and evolution occurs at the end of the last of the Snowball glaciations, where complex life is first found in the fossil record. Significant concentrations of oxygen were just one of the prerequisites for the evolution of complex life, models based on uniformitarian principles suggest that such a concentration was only reached immediately before metazoa first appeared in the fossil record. First breath, Earths billion-year struggle for oxygen New Scientist, #2746,5 February 2010 by Nick Lane, the Mystery of Earths Oxygen New York Times,3 October 2013 by Carl Zimmer
Geological history of oxygen
29.
Great Oxygenation Event
–
The Great Oxygenation Event was the biologically induced appearance of dioxygen in Earths atmosphere. The current geochemical and biomarker evidence for the development of oxygenic photosynthesis before the Great Oxidation Event has been mostly inconclusive. Oceanic cyanobacteria, which evolved into multicellular forms more than 2.3 billion years ago, are believed to have become the first microbes to produce oxygen by photosynthesis, before the GOE, any free oxygen they produced was chemically captured by dissolved iron or organic matter. The GOE was the point in time when these oxygen sinks became saturated, at which point oxygen, the increased production of oxygen set Earths original atmosphere off balance. Free oxygen is toxic to anaerobic organisms, and the rising concentrations may have destroyed most such organisms at the time. Cyanobacteria were therefore responsible for one of the most significant extinction events in Earths history, besides marine cyanobacteria, there is also evidence of cyanobacteria on land. A spike in chromium contained in ancient rock deposits formed underwater shows they had accumulated chromium washed off from continental shelves, chromium is not easily dissolved and its release from rocks would have required the presence of a powerful acid. One such acid, sulfuric acid, might have created through bacterial reactions with pyrite. Eventually, the evolution of organisms that consumed oxygen established an equilibrium in its availability. Free oxygen has been an important constituent of the atmosphere ever since, the excess of oxygen those organisms produce is a waste product. These organisms lived long before the GOE, perhaps as early as 3,500 million years ago, initially, the oxygen they produced would have quickly been removed from the atmosphere by the chemical weathering of reducing minerals, most notably iron. This mass rusting led to the deposition of oxide in the form of banded-iron formations such as the sediments in Minnesota and Pilbara. Oxygen only began to persist in the atmosphere in small quantities shortly before the start of the GOE, without a mineral sink in the form of iron, oxygen could have accumulated very rapidly. For example, at rates of photosynthesis, modern atmospheric O2 levels could be produced in around 2,000 years. Another hypothesis is that producers did not evolve until just before the major rise in atmospheric oxygen concentration. This is based on interpretation of the oxygen indicator, mass-independent fractionation of sulfur isotopes. This hypothesis would eliminate the need to explain a lag in time between the evolution of oxyphotosynthetic microbes and the rise in free oxygen.4 to 2.1 billion years ago. The latter may have been a full-blown, and possibly the longest ever, snowball Earth episode, despite the natural recycling of organic matter, life had remained energetically limited until the widespread availability of oxygen
Great Oxygenation Event
–
Timeline of glaciations, shown in blue.
Great Oxygenation Event
–
2.1 billion year old rock showing banded iron formation
. PMID 26483481. doi:10.1073/pnas.1517557112. Retrieved 2015-10-20. Early edition, published online before print.
