Red Crag Formation
The Red Crag Formation is a geological formation in England. It outcrops in south-eastern north-eastern Essex; the name derives from its iron-stained reddish colour and crag, an East Anglian word for shells. It is part of the Crag Group, a series of notably marine strata which belong to a period when Britain was connected to continental Europe by the Weald–Artois Anticline, the area in which the Crag Group was deposited was a tidally dominated marine bay; this bay would have been subjected to enlargement and contraction brought about by transgressions and regressions driven by the 40,000-year Milankovitch cycles. The sediment in the outcrops consists of coarse-grained and shelly sands that were deposited in sand waves that migrated parallel to the shore in a south-westward direction; the most common fossils are bivalves and gastropods that were worn by the abrasive environment. The most extensive exposure is found at Bawdsey Cliff, designated a Site of Special Scientific Interest. At the coastline by Walton-on-the-Naze, remains of Megalodon were found.
The Red Crag Formation at depth in eastern Suffolk has one member, the Sizewell Member, a coarse shelly sand with thin beds of clay and silt. It was interpreted as having been deposited in large scale sand waves; the overlying Thorpeness Member, was provisionally assigned to the Red Crag based on its lithology but there is more evidence to suggest that it is part of the Norwich Crag Formation. It has been proposed that the Red Crag started in the late Pliocene and to have extended up into the early Pleistocene, but there is disagreement on more precise dating. According to the British Geological Survey, the Red Crag sits within a segment of time from about 3.3 to 2.5 mya. It is considered that the Red Crag at Walton-on-the–Naze is the oldest and that it was deposited in only a few decades at some time between 2.9 and 2.6 mya. This has led to the UK stratigraphic stage name Waltonian, correlated with the final Pliocene Reuverian Stage in the Netherlands. There are difficulties in reconciling how the Red Crag equates with international chronological stages.
In particular, the start and end dates are poorly defined due to the general paucity of age-diagnostic stratigraphic indicators and the fragmentary nature of the geology. It can be difficult to separate the Red Crag from the overlying Norwich Crag Formation. Lee, J. R.. British Regional Geology: East Anglia. British Geological Survey. ISBN 978-0-85272-823-9
Plankton are the diverse collection of organisms that live in large bodies of water and are unable to swim against a current. The individual organisms constituting plankton are called plankters, they provide a crucial source of food to many large aquatic organisms, such as fish and whales. These organisms include bacteria, algae and drifting or floating animals that inhabit—for example—the pelagic zone of oceans, seas, or bodies of fresh water. Plankton are defined by their ecological niche rather than any phylogenetic or taxonomic classification. Though many planktonic species are microscopic in size, plankton includes organisms over a wide range of sizes, including large organisms such as jellyfish. Technically the term does not include organisms on the surface of the water, which are called pleuston—or those that swim in the water, which are called nekton; the name plankton is derived from the Greek adjective πλαγκτός, meaning errant, by extension, wanderer or drifter, was coined by Victor Hensen in 1887.
While some forms are capable of independent movement and can swim hundreds of meters vertically in a single day, their horizontal position is determined by the surrounding water movement, plankton flow with ocean currents. This is in contrast to nekton organisms, such as fish and marine mammals, which can swim against the ambient flow and control their position in the environment. Within the plankton, holoplankton spend their entire life cycle as plankton. By contrast, meroplankton are only planktic for part of their lives, graduate to either a nektic or benthic existence. Examples of meroplankton include the larvae of sea urchins, crustaceans, marine worms, most fish; the amount and distribution of plankton depends on available nutrients, the state of water and a large amount of other plankton. The study of plankton is termed planktology and a planktonic individual is referred to as a plankter; the adjective planktonic is used in both the scientific and popular literature, is a accepted term.
However, from the standpoint of prescriptive grammar, the less-commonly used planktic is more the correct adjective. When deriving English words from their Greek or Latin roots, the gender-specific ending is dropped, using only the root of the word in the derivation. Plankton are divided into broad functional groups: Phytoplankton, autotrophic prokaryotic or eukaryotic algae that live near the water surface where there is sufficient light to support photosynthesis. Among the more important groups are the diatoms, cyanobacteria and coccolithophores. Zooplankton, small protozoans or metazoans that feed on other plankton; some of the eggs and larvae of larger nektonic animals, such as fish and annelids, are included here. Bacterioplankton and archaea, which play an important role in remineralising organic material down the water column. Mycoplankton and fungus-like organisms, like bacterioplankton, are significant in remineralisation and nutrient cycling; this scheme divides the plankton community into broad producer and recycler groups.
However, determining the trophic level of many plankton is not always straightforward. For example, although most dinoflagellates are either photosynthetic producers or heterotrophic consumers, many species perform both roles. In this mixed trophic strategy — known as mixotrophy — organisms act as both producers and consumers, either at the same time or switching between modes of nutrition in response to ambient conditions. For instance, relying on photosynthesis for growth when nutrients and light are abundant, but switching to predation when growing conditions are poor. Recognition of the importance of mixotrophy as an ecological strategy is increasing, as well as the wider role this may play in marine biogeochemistry. Plankton are often described in terms of size; the following divisions are used: However, some of these terms may be used with different boundaries on the larger end. The existence and importance of nano- and smaller plankton was only discovered during the 1980s, but they are thought to make up the largest proportion of all plankton in number and diversity.
The microplankton and smaller groups are microorganisms and operate at low Reynolds numbers, where the viscosity of water is much more important than its mass or inertia. Plankton inhabit oceans, lakes, ponds. Local abundance varies horizontally and seasonally; the primary cause of this variability is the availability of light. All plankton ecosystems are driven by the input of solar energy, confining primary production to surface waters, to geographical regions and seasons having abundant light. A secondary variable is nutrient availability. Although large areas of the tropical and sub-tropical oceans have abundant light, they experience low primary production because they offer limited nutrients such as nitrate and silicate; this results from large-scale ocean water column stratification. In such regions, primary production occurs at greater depth, although at a reduced level. Despite significant macronutrient concentrations, some ocean regions are unproductive; the micronutrient iron is deficient in these reg
Abrupt climate change
An abrupt climate change occurs when the climate system is forced to transition to a new climate state at a rate, determined by the climate system energy-balance, and, more rapid than the rate of change of the external forcing. Past events include the end of the Carboniferous Rainforest Collapse, Younger Dryas, Dansgaard-Oeschger events, Heinrich events and also the Paleocene–Eocene Thermal Maximum; the term is used within the context of global warming to describe sudden climate change, detectable over the time-scale of a human lifetime as the result of feedback loops within the climate system. Timescales of events described as'abrupt' may vary dramatically. Changes recorded in the climate of Greenland at the end of the Younger Dryas, as measured by ice-cores, imply a sudden warming of +10 °C within a timescale of a few years. Other abrupt changes are the +4 °C on Greenland 11,270 years ago or the abrupt +6 °C warming 22,000 years ago on Antarctica. By contrast, the Paleocene-Eocene thermal maximum may have initiated anywhere between a few decades and several thousand years.
Earth Systems models project that under ongoing greenhouse gas emissions as early as 2047, the Earth's near surface temperature could depart from the range of variability in the last 150 years, affecting over 3 billion people and most places of great species diversity on Earth. According to the Committee on Abrupt Climate Change of the National Research Council: There are two definitions of abrupt climate change: In terms of physics, it is a transition of the climate system into a different mode on a time scale, faster than the responsible forcing. In terms of impacts, "an abrupt change is one that takes place so and unexpectedly that human or natural systems have difficulty adapting to it"; these definitions are complementary: the former gives some insight into how abrupt climate change comes about. Possible tipping elements in the climate system include: regional effects of global warming, some of which had abrupt onset and may therefore be regarded as abrupt climate change. Scientists have stated that "Our synthesis of present knowledge suggests that a variety of tipping elements could reach their critical point within this century under anthropogenic climate change."It has been postulated that teleconnections and atmospheric processes, on different timescales, connect both hemispheres during abrupt climate change.
The IPCC states that global warming "could lead to some effects that are abrupt or irreversible". A 2013 report from the U. S. National Research Council called for attention to the abrupt impacts of climate change, stating that steady, gradual change in the physical climate system can have abrupt impacts elsewhere—in human infrastructure and ecosystems for example—if critical thresholds are crossed; the report emphasizes the need for an early warning system that could help society better anticipate sudden changes and emerging impacts. Scientific understanding of abrupt climate change is poor; the probability of abrupt change for some climate related. Factors that may increase the probability of abrupt climate change include higher magnitudes of global warming, warming that occurs more and warming, sustained over longer time periods. Climate models are unable yet to predict abrupt climate change events, or most of the past abrupt climate shifts. A potential abrupt feedback due to thermokarst lake formations in the Arctic, in response to thawing permafrost soils, releasing additional greenhouse gas methane, is not accounted for in climate models.
Most abrupt climate shifts, are due to sudden circulation shifts, analogous to a flood cutting a new river channel. The best-known examples are the several dozen shutdowns of the North Atlantic Ocean's Meridional Overturning Circulation during the last ice age, affecting climate worldwide; the current warming of the Arctic, the duration of the summer season, is considered abrupt and massive. Antarctic ozone depletion caused significant atmospheric circulation changes. There have been two occasions when the Atlantic's Meridional Overturning Circulation lost a crucial safety factor; the Greenland Sea flushing at 75 °. The second-largest flushing site, the Labrador Sea, shut down in 1997 for ten years. While shutdowns overlapping in time have not been seen during the fifty years of observation, previous total shutdowns had severe worldwide climate consequences. Abrupt climate change has been the cause of wide ranging and severe effects: Mass extinctions in the past, most notably the Permian-Triassic Extinction event and the Carboniferous Rainforest Collapse, have been suggested as a consequence of abrupt climate change.
Loss of biodiversity. Without interference from abrupt climate change and other extinction events the biodiversity of this planet would continue to grow. Changes in ocean circulation such asIncreasing frequency of El Niño events Potential disruption to the thermohaline circulation, such as that which may have occurred during the Younger Dryas event. Changes to the North Atlantic oscillation Changes in Atlantic Meridional Overturning Circulation which could contribute to more severe weather events. One source of abrupt climate change effects is a feedback process, in which a warming event causes a change which leads to further warming; this can apply to cooling. Example of such feedback processes are: Ice-albedo feedback, where the advance or retreat of ice cover alters the'whiteness' of the earth, its ability to absorb the sun's energy. Soil carbon feedback concerns releases of
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present. As with other older geologic periods, the rock beds that define the epoch are well identified but the exact dates of the start and end of the epoch are uncertain; the name Oligocene was coined in 1854 by the German paleontologist Heinrich Ernst Beyrich. The Oligocene is followed by the Miocene Epoch; the Oligocene is the final epoch of the Paleogene Period. The Oligocene is considered an important time of transition, a link between the archaic world of the tropical Eocene and the more modern ecosystems of the Miocene. Major changes during the Oligocene included a global expansion of grasslands, a regression of tropical broad leaf forests to the equatorial belt; the start of the Oligocene is marked by a notable extinction event called the Grande Coupure. By contrast, the Oligocene–Miocene boundary is not set at an identified worldwide event but rather at regional boundaries between the warmer late Oligocene and the cooler Miocene.
Oligocene faunal stages from youngest to oldest are: The Paleogene Period general temperature decline is interrupted by an Oligocene 7-million-year stepwise climate change. A deeper 8.2 °C, 400,000-year temperature depression leads the 2 °C, seven-million-year stepwise climate change 33.5 Ma. The stepwise climate change began 32.5 Ma and lasted through to 25.5 Ma, as depicted in the PaleoTemps chart. The Oligocene climate change was a global increase in ice volume and a 55 m decrease in sea level with a related temperature depression; the 7-million-year depression abruptly terminated within 1–2 million years of the La Garita Caldera eruption at 28–26 Ma. A deep 400,000-year glaciated Oligocene Miocene boundary event is recorded at McMurdo Sound and King George Island. During this epoch, the continents continued to drift toward their present positions. Antarctica became more isolated and developed an ice cap. Mountain building in western North America continued, the Alps started to rise in Europe as the African plate continued to push north into the Eurasian plate, isolating the remnants of the Tethys Sea.
A brief marine incursion marks the early Oligocene in Europe. Marine fossils from the Oligocene are rare in North America. There appears to have been a land bridge in the early Oligocene between North America and Europe, since the faunas of the two regions are similar. Sometime during the Oligocene, South America was detached from Antarctica and drifted north towards North America, it allowed the Antarctic Circumpolar Current to flow cooling the Antarctic continent. Angiosperms continued their expansion throughout the world as tropical and sub-tropical forests were replaced by temperate deciduous forests. Open plains and deserts became more common and grasses expanded from their water-bank habitat in the Eocene moving out into open tracts; however at the end of the period, grass was not quite common enough for modern savannas. In North America, subtropical species dominated with cashews and lychee trees present, temperate trees such as roses and pines were common; the legumes spread, while sedges and ferns continued their ascent.
More open landscapes allowed animals to grow to larger sizes than they had earlier in the Paleocene epoch 30 million years earlier. Marine faunas became modern, as did terrestrial vertebrate fauna on the northern continents; this was more as a result of older forms dying out than as a result of more modern forms evolving. Many groups, such as equids, rhinos and camelids, became more able to run during this time, adapting to the plains that were spreading as the Eocene rainforests receded; the first felid, originated in Asia during the late Oligocene and spread to Europe. South America was isolated from the other continents and evolved a quite distinct fauna during the Oligocene; the South American continent became home to strange animals such as pyrotheres and astrapotheres, as well as litopterns and notoungulates. Sebecosuchians, terror birds, carnivorous metatheres, like the borhyaenids remained the dominant predators. Brontotheres died out in the Earliest Oligocene, creodonts died out outside Africa and the Middle East at the end of the period.
Multituberculates, an ancient lineage of primitive mammals that originated back in the Jurassic became extinct in the Oligocene, aside from the gondwanatheres. The Oligocene was home to a wide variety of strange mammals. A good example of this would be the White River Fauna of central North America, which were a semiarid prairie home to many different types of endemic mammals, including entelodonts like Archaeotherium, running rhinoceratoids, three-toed equids, nimravids and early canids like Hesperocyon. Merycoidodonts, an endemic American group, were diverse during this time. In Asia during the Oligocene, a group of running rhinoceratoids gave rise to the indricotheres, like Paraceratherium, which were the largest land mammals to walk the Earth; the marine animals of Oligocene oceans resembled today's fauna, such as the bivalves. Calcareous cirratulids appeared in the Oligocene; the fossil record of marine mammals is a little spotty during this time, not as well known as the Eocene o
Homo habilis is a proposed archaic species of Homo, which lived between 2.1 and 1.5 million years ago, during the Gelasian and early Calabrian stages of the Pleistocene geological epoch. The type specimen is OH 7, discovered in 1960 at Olduvai Gorge in Tanzania, associated with the Oldowan lithic industry. In its appearance and morphology, H. habilis is intermediate between Australopithecus and the somewhat younger Homo erectus and its classification in the genus Homo has been the subject of controversial debate since its original proposal. A main argument for its classification as the first Homo species was its use of flaked stone tools. However, evidence for earlier tool use by undisputed members of Australopithecus has been found in the 1990s. In January 2019, scientists reported that Australopithecus sediba is distinct from, but shares anatomical similarities to, both the older Australopithecus africanus, the younger Homo habilis. There has been scholarly debate regarding its placement in the genus Homo rather than the genus Australopithecus.
The small size and rather primitive attributes have led some experts to propose excluding H. habilis from the genus Homo and placing them instead in Australopithecus as Australopithecus habilis. Louis Leakey, the British-Kenyan paleoanthropologist, the first to suggest the existence of H. habilis, his wife, Mary Leakey, found the first trace of H. habilis in 1955: two hominin teeth. These were classified as "milk teeth", therefore considered difficult to link to taxa, unlike permanent teeth. H. habilis had disproportionately long arms compared to modern humans. H. habilis had a cranial capacity less than half of the size of modern humans. Despite the ape-like morphology of the bodies, H. habilis remains are accompanied by primitive stone tools. Homo habilis has been thought to be the ancestor of the more gracile and sophisticated Homo ergaster, which in turn gave rise to the more human-appearing species, Homo erectus. Debates continue over whether all of the known fossils are properly attributed to the species, some paleoanthropologists regard the taxon as invalid, made up of fossil specimens of Australopithecus and Homo.
New findings in 2007 seemed to confirm the view that H. habilis and H. erectus coexisted, representing separate lineages from a common ancestor instead of H. erectus being descended from H. habilis. An alternative explanation would be that any ancestral relationship from H. habilis to H. erectus would have to have been cladogenetic rather than anagenetic. Discoveries at Dmanisi, which had diverse physical traits and differences in tooth wear, suggest to some scholars that all the contemporary groups of early Homo in Africa, including Homo ergaster, Homo habilis, Homo rudolfensis are of the same species and should be assigned to Homo erectus, with the implication that variation between these “species” represents the prolonged evolution of one lineage, rather than interspecific differences. H. habilis brain size has been shown to range from 550 cubic centimetres to 687 cubic centimetres, rather than from 363 cubic centimetres to 600 cubic centimetres as thought. A virtual reconstruction published in 2015 estimated the endocranial volume at between 729 millilitres and 824 millilitres, larger than any published value.
H. Habilis' brain capacity of around 640 cm³ was on average 50% larger than australopithecines, but smaller than the 1,350 cubic centimetres to 1,450 cubic centimetres range of modern Homo sapiens; these hominins were smaller on average standing no more than 1.3 metres. The body proportions for H. habilis are in accordance with craniodental evidence, suggesting closer association with H. erectus. Based on dental microwear-texture analysis, Homo habilis did not specialize on tough foods. Microwear-texture complexity is, on average, somewhere between that of tough-food feeders and leaf feeders These measurements are analyses of the percentages of tooth surface structure containing "pits", it is a used, henceforth accepted as reliable, measure of wear that a species, on average, endures from eating certain food. These measurements point to an generalized, omnivorous diet in Homo habilis. Homo habilis is thought to have mastered the Lower Paleolithic Olduwan tool set, which used stone flakes. H. habilis used these stones to skin animals.
These stone flakes were more advanced than any tools used, gave H. habilis the edge it needed to prosper in hostile environments too formidable for primates. Whether H. habilis was the first hominin to master stone tool technology remains controversial, as Australopithecus garhi, dated to 2.6 million years ago, has been found along with stone tool implements. Most experts assume the intelligence and social organization of H. habilis were more sophisticated than typical australopithecines
Discoaster is a genus of extinct star-shaped marine algae, with calcareous exoskeletons of between 5-40 μm across that are abundant as nanofossils in tropical deep-ocean deposits of Neogene age. Discoaster belongs to the haptophytes. About 100 species can be recognized; the International Commission on Stratigraphy has assigned the extinction of Discoaster brouweri as the defining biological marker for the start of the Calabrian Stage of the Pleistocene, 1.806 million years ago. ICS has assigned the extinction of Discoaster pentaradiatus and Discoaster surculus as the defining biological marker for the start of the Gelasian Stage, 2.588 million years ago, the earliest stage of the Pleistocene. ICS further assigned the extinction of Discoaster kugleri as biological marker for the start of the Tortonian Stage of the Miocene, 11.62 million years ago. Some species in this genus include: D. asymmetricus Gartner D. bellus Bukry and Percival D. berggrenii Bukry D. bollii Martini and Bramlette D. brouweri Bramlette and Riedel D. calcaris Gartner D. exilis Martini and Bramlette D. hamatus Martini and Bramlette D. intercalaris Bukry D. kugleri Martini and Bramlette, 1963 D. loeblichii Bukry D. neohamatus Bukry and Bramlette D. neorectus Bukry D. pentaradiatus Bramlette and Riedel D. quintatus Gartner D. surculus Martini and Bramlette D. toralus Ellis and Wray D. triradiatus Tan D. variabilis Martini and Bramlette