North America is a continent within the Northern Hemisphere and all within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, to the southeast by South America and the Caribbean Sea. North America covers an area of about 24,709,000 square kilometers, about 16.5% of the earth's land area and about 4.8% of its total surface. North America is the third largest continent by area, following Asia and Africa, the fourth by population after Asia and Europe. In 2013, its population was estimated at nearly 579 million people in 23 independent states, or about 7.5% of the world's population, if nearby islands are included. North America was reached by its first human populations during the last glacial period, via crossing the Bering land bridge 40,000 to 17,000 years ago; the so-called Paleo-Indian period is taken to have lasted until about 10,000 years ago. The Classic stage spans the 6th to 13th centuries.
The Pre-Columbian era ended in 1492, the transatlantic migrations—the arrival of European settlers during the Age of Discovery and the Early Modern period. Present-day cultural and ethnic patterns reflect interactions between European colonists, indigenous peoples, African slaves and their descendants. Owing to the European colonization of the Americas, most North Americans speak English, Spanish or French, their culture reflects Western traditions; the Americas are accepted as having been named after the Italian explorer Amerigo Vespucci by the German cartographers Martin Waldseemüller and Matthias Ringmann. Vespucci, who explored South America between 1497 and 1502, was the first European to suggest that the Americas were not the East Indies, but a different landmass unknown by Europeans. In 1507, Waldseemüller produced a world map, in which he placed the word "America" on the continent of South America, in the middle of what is today Brazil, he explained the rationale for the name in the accompanying book Cosmographiae Introductio:... ab Americo inventore... quasi Americi terram sive Americam.
For Waldseemüller, no one should object to the naming of the land after its discoverer. He used the Latinized version of Vespucci's name, but in its feminine form "America", following the examples of "Europa", "Asia" and "Africa". Other mapmakers extended the name America to the northern continent, In 1538, Gerard Mercator used America on his map of the world for all the Western Hemisphere; some argue that because the convention is to use the surname for naming discoveries, the derivation from "Amerigo Vespucci" could be put in question. In 1874, Thomas Belt proposed a derivation from the Amerrique mountains of Central America. Marcou corresponded with Augustus Le Plongeon, who wrote: "The name AMERICA or AMERRIQUE in the Mayan language means, a country of perpetually strong wind, or the Land of the Wind, and... the can mean... a spirit that breathes, life itself." The United Nations formally recognizes "North America" as comprising three areas: Northern America, Central America, The Caribbean.
This has been formally defined by the UN Statistics Division. The term North America maintains various definitions in accordance with context. In Canadian English, North America refers to the land mass as a whole consisting of Mexico, the United States, Canada, although it is ambiguous which other countries are included, is defined by context. In the United States of America, usage of the term may refer only to Canada and the US, sometimes includes Greenland and Mexico, as well as offshore islands. In France, Portugal, Romania and the countries of Latin America, the cognates of North America designate a subcontinent of the Americas comprising Canada, the United States, Mexico, Greenland, Saint Pierre et Miquelon, Bermuda. North America has been referred to by other names. Spanish North America was referred to as Northern America, this was the first official name given to Mexico. Geographically the North American continent has many subregions; these include cultural and geographic regions. Economic regions included those formed by trade blocs, such as the North American Trade Agreement bloc and Central American Trade Agreement.
Linguistically and culturally, the continent could be divided into Latin America. Anglo-America includes most of Northern America and Caribbean islands with English-speaking populations; the southern North American continent is composed of two regions. These are the Caribbean; the north of the continent maintains recognized regions as well. In contrast to the common definition of "North America", which encompasses the whole continent, the term "North America" is sometimes used to refer only to Mexico, the United States, Greenland; the term Northern America refers to the northern-most countries and territories of North America: the United States, Bermuda, St. Pierre and Miquelon and Greenland. Although the term does not refer to a unifie
Quaternary extinction event
The Quaternary period saw the extinctions of numerous predominantly megafaunal species, which resulted in a collapse in faunal density and diversity and the extinction of key ecological strata across the globe. The most prominent event in the Late Pleistocene is differentiated from previous Quaternary pulse extinctions by the widespread absence of ecological succession to replace these extinct species, the regime shift of established faunal relationships and habitats as a consequence; the earliest casualties were incurred at 130,000 BCE. However, the great majority of extinctions in Afro-Eurasia and the Americas occurred during the transition from the Pleistocene to the Holocene epoch; this extinction wave did not stop at the end of the Pleistocene, continuing on isolated islands, in human-caused extinctions, although there is debate as to whether these should be considered separate events or part of the same event. Among the main causes hypothesized by paleontologists are overkill by the widespread appearance of humans and natural climate change.
A notable modern human presence first appeared during the Middle Pleistocene in Africa, started to establish continuous, permanent populations in Eurasia and Australasia from 120,000 BCE and 63,000 BCE and the Americas from 22,000 BCE. A variant of the former possibility is the second-order predation hypothesis, which focuses more on the indirect damage caused by overcompetition with nonhuman predators. Recent studies have tended to favor the human-overkill theory; the Late Pleistocene extinction event saw the extinction of many mammals weighing more than 40 kg. The proportional rate of megafauna extinctions is progressively larger the greater the human migratory distance from Africa. In Subsaharan Africa, 8 of 50 genera of mammalian megafauna were driven to extinction. In Asia, 24 of 46 In Europe, 23 of 39 In Australasia, 19 of 27 In North America, 45 of 61 In South America, 58 of 71 The extinctions in the Americas entailed the elimination of all the larger mammalian species of South American origin, including those that had migrated north in the Great American Interchange.
Only in the continents of Australia, North America, South America did the extinction occur at family taxonomic levels or higher. The proportional rate of megafauna extinctions being incrementally bigger the larger the migratory distance from Africa might be related to non-African megafauna and Homo sapiens having not evolved as species alongside each other. For their part, North America and South America, which had the highest incremental extinction rates, had no known native species of Hominoidea at all, no species of Hominidae or Homo; the increased rate of extinction mirrors the sequential pattern of the migration of anatomically modern humans. The further away from Africa, the more the area has been inhabited by humans, the less time the environments had had to become accustomed to humans and vice versa. There is no evidence of megafaunal extinctions at the height of the Last Glacial Maximum, indicating that increasing cold and glaciation were not factors. There are three main hypotheses concerning the Pleistocene extinction: climate change associated with the advance and retreat of major ice caps or ice sheets.
"prehistoric overkill hypothesis" the extinction of the woolly mammoth changed the extensive grasslands to birch forests, subsequent forest fires changed the climate. We now know that after the extinction of the mammoth, birch forests replaced the grasslands and that an era of significant fire began. There are some inconsistencies between the current available data and the prehistoric overkill hypothesis. For instance, there are ambiguities around the timing of sudden extinctions of Australian megafauna. Biologists note that comparable extinctions have not occurred in Africa and South or Southeast Asia, where the fauna evolved with hominids. Post-glacial megafaunal extinctions in Africa have been spaced over a longer interval. Evidence supporting the prehistoric overkill hypothesis includes the persistence of certain island megafauna for several millennia past the disappearance of their continental cousins. Ground sloths survived on the Antilles long after North and South American ground sloths were extinct.
The disappearance of the island species correlates with the colonization of these islands by humans. Woolly mammoths died out on remote Wrangel Island 1,000 years after their extinction on the mainland. Steller's sea cows persisted in seas off the isolated and uninhabited Commander Islands for thousands of years after they had vanished from the continental shores of the north Pacific. Alternative hypotheses to the theory of human responsibility include climate change associated with the last glacial period and the Younger Dryas event, as well as Tollmann's hypothetical bolide, which claim that the extinctions resulted from bolide impact; such a scenario has been proposed as a contributing cause of the 1,300-year cold period known as the Younger Dryas stadial. This impact extinction hypothesis is still in debate due to the exacting field techniques required to extract minuscule particles of extraterrestrial impact markers such as iridium at a high resolution from thin strata in a repeatable fashion, as is necessary to conclusively distinguish the event peak from the local background level of the marker.
The debate seems to be exacerbated by infighting between the Uniformitarianism camp and the Catastrophism camp. Recent research indicates that each single species responded differently to environm
The Upper Paleolithic is the third and last subdivision of the Paleolithic or Old Stone Age. Broadly, it dates to between 50,000 and 10,000 years ago, according to some theories coinciding with the appearance of behavioral modernity and before the advent of agriculture. Anatomically modern humans are believed to have emerged out of Africa around 200,000 years ago, although these lifestyles changed little from that of archaic humans of the Middle Paleolithic, until about 50,000 years ago, when there was a marked increase in the diversity of artefacts; this period coincides with the expansion of modern humans from Africa throughout Asia and Eurasia, which contributed to the extinction of the Neanderthals. The Upper Paleolithic has the earliest known evidence of organized settlements, in the form of campsites, some with storage pits. Artistic work blossomed, with cave painting, petroglyphs and engravings on bone or ivory; the first evidence of human fishing is found, from artefacts in places such as Blombos cave in South Africa.
More complex social groupings emerged, supported by more varied and reliable food sources and specialized tool types. This contributed to increasing group identification or ethnicity; the peopling of Australia most took place before c. 60 ka. Europe was peopled after c. 45 ka. Anatomically modern humans are known to have expanded northward into Siberia as far as the 58th parallel by about 45 ka; the Upper Paleolithic is divided during about 25 to 15 ka. The peopling of the Americas occurred during this time, with East and Central Asia populations reaching the Bering land bridge after about 35 ka, expanding into the Americas by about 15 ka. In Western Eurasia, the Paleolithic eases into the so-called Epipaleolithic or Mesolithic from the end of the LGM, beginning 15 ka; the Holocene glacial retreat begins 11.7 ka, falling well into the Old World Epipaleolithic, marking the beginning of the earliest forms of farming in the Fertile Crescent. Both Homo erectus and Neanderthals used the same crude stone tools.
Archaeologist Richard G. Klein, who has worked extensively on ancient stone tools, describes the stone tool kit of archaic hominids as impossible to categorize, it was as if the Neanderthals made stone tools, were not much concerned about their final forms. He argues that everywhere, whether Asia, Africa or Europe, before 50,000 years ago all the stone tools are much alike and unsophisticated. Firstly among the artefacts of Africa, archeologists found they could differentiate and classify those of less than 50,000 years into many different categories, such as projectile points, engraving tools, knife blades, drilling and piercing tools; these new stone-tool types have been described as being distinctly differentiated from each other. The invaders referred to as the Cro-Magnons, left many sophisticated stone tools and engraved pieces on bone and antler, cave paintings and Venus figurines; the Neanderthals continued to use Mousterian stone tool technology and Chatelperronian technology. These tools disappeared from the archeological record at around the same time the Neanderthals themselves disappeared from the fossil record, about 40,000 cal BP.
Settlements were located in narrow valley bottoms associated with hunting of passing herds of animals. Some of them may have been occupied year round, though more they appear to have been used seasonally. Hunting was important, caribou/wild reindeer "may well be the species of single greatest importance in the entire anthropological literature on hunting."Technological advances included significant developments in flint tool manufacturing, with industries based on fine blades rather than simpler and shorter flakes. Burins and racloirs were used to work bone and hides. Advanced darts and harpoons appear in this period, along with the fish hook, the oil lamp and the eyed needle; the changes in human behavior have been attributed to changes in climate, encompassing a number of global temperature drops. These led to a worsening of the bitter cold of the last glacial period; such changes may have reduced the supply of usable timber and forced people to look at other materials. In addition, flint may not have functioned as a tool.
Some scholars argue that the appearance of complex or abstract language made these behavior changes possible. The complexity of the new human capabilities hints that humans were less capable of planning or foresight before 40,000 years, while the emergence of cooperative and coherent communication marked a new era of cultural development; the climate of the period in Europe saw dramatic changes, included the Last Glacial Maximum, the coldest phase of the last glacial period, which lasted from about 26.5 to 19 kya, being coldest at the end, before a rapid warming. During the Maximum, most of Northern Europe was covered by an ice-sheet, forcing human populations into the areas known as Last Glacial Maximum refugia, including modern Italy and the Balkans, parts of the Iberian Peninsula and areas around the Black Sea; this period saw cultures such as the Solutrean in Spain. Human life may have continued on top of the ice sheet, but we know next to nothing about it, little about the human life that preceded the European glaciers.
In the early part of the period, up to a
Bison antiquus, the ancient or antique bison, is an extinct species of bison that lived in North America until around 10,000 years ago. It was one of the most common large herbivores on the North American continent during the late Pleistocene, is a direct ancestor of the living American bison. During the Pleistocene epoch, between 240,000 and 220,000 years ago, steppe wisent migrated from Siberia into Alaska across the Bering Land Bridge. Bison priscus inhabited northern North America throughout the remainder of the Pleistocene. In western North America, B. priscus evolved into long-horned bison, B. latifrons, which evolved into B. antiquus. The larger B. latifrons appears to have died out by about 20,000 years ago. After the extinction of B. latifrons, B. antiquus became abundant in parts of midcontinent North America from 18,000 ya until about 10,000 ya, after which the species appears to have given rise to the living species, B. bison. B. antiquus is the most recovered large mammalian herbivore from the La Brea tar pits.
B. Antiquus was taller, had larger bones and horns, was 15-25% larger overall than modern bison, it reached up to 2.27 m tall, 4.6 m long, a weight of 1,588 kg. From tip to tip, the horns of B. antiquus measured about 3 ft. One of the best educational sites to view in situ semifossilized skeletons of over 500 individuals of B. antiquus is the Hudson-Meng archeological site operated by the U. S. Forest Service, 18 miles northwest of Crawford, Nebraska. A number of paleo-Indian spear and projectile points have been recovered in conjunction with the animal skeletons at the site, dated around 9,700 to 10,000 years ago; the reason for the "die-off" of so many animals in one compact location is still in conjecture. Individuals of B. antiquus of both sexes and a typical range of ages have been found at the site. According to internationally renowned archaeologist George Carr Frison, B. occidentalis and B. antiquus, an extinct subspecies of the smaller present-day bison, survived the Late Pleistocene period, between about 12,000 and 11,000 years ago, dominated by glaciation, when many other megafauna became extinct.
Plains and Rocky Mountain First Nations peoples depended on these bison as their major food source. Frison noted that the "oldest, well-documented bison kills by pedestrian human hunters in North America date to about 11,000 years ago." Davis, L. B.. L. Quaternary Glaciations: Extent and Chronology 2: Part II North America, Amsterdam: Elsevier, ISBN 0-444-51462-7 Frison, George C. Prehistoric Human and Bison Relationships on the Plains of North America, Alberta: International Bison Conference Leidy, Joseph, "Bison antiquus", Proceedings Academy of Natural Science, 6: 117 Leidy, Memoir on the extinct species of American ox, retrieved 20 September 2013 Conrad, Jim. "Ancient Bison foot fossil". The Loess Hills of the Lower Mississippi Valley. Backyard Nature. Retrieved 19 September 2013. Paleobiology Database - Bison antiquus
A number of varieties of Homo are grouped into the broad category of archaic humans in the period contemporary to and predating the emergence of the earliest anatomically modern humans over 315 ka. The term includes Homo neanderthalensis, Homo rhodesiensis, Homo heidelbergensis, Homo antecessor. There is no universal consensus on this terminology, varieties of "archaic humans" are included under the binomial name of either Homo sapiens or Homo erectus by some authors. Archaic humans had a brain size averaging 1,200 to 1,400 cubic centimeters, which overlaps with the range of modern humans. Archaics are distinguished from anatomically modern humans by having a thick skull, prominent supraorbital ridges and the lack of a prominent chin. Anatomically modern humans appear from over 160,000 years ago in Ethiopia and after 70,000 years ago supplanting the "archaic" human varieties. Non-modern varieties of Homo are certain to have survived until after 30,000 years ago, until as as 12,000 years ago.
Which of these, if any, are included under the term "archaic human" is a matter of definition and varies among authors. Nonetheless, according to recent genetic studies, modern humans may have bred with "at least two groups" of ancient humans: Neanderthals and Denisovans. Other studies have cast doubt on admixture being the source of the shared genetic markers between archaic and modern humans, pointing to an ancestral origin of the traits which originated 500,000–800,000 years ago. Another group may have been extant as as 11,500 years ago, the Red Deer Cave people of China. Chris Stringer of the Natural History Museum in London has suggested that these people could be a result of mating between Denisovans and modern humans. Other scientists remain skeptical, suggesting that the unique features are within the variations expected for modern human populations; the category archaic human lacks a single, agreed upon definition. According to one definition, Homo sapiens is a single species comprising several subspecies that include the archaics and modern humans.
Under this definition, modern humans are referred to as Homo sapiens sapiens and archaics are designated with the prefix "Homo sapiens". For example, the Neanderthals are Homo sapiens neanderthalensis, Homo heidelbergensis is Homo sapiens heidelbergensis. Other taxonomists prefer not to consider archaics and modern humans as a single species but as several different species. In this case the standard taxonomy is used, Homo neanderthalensis; the evolutionary dividing lines that separate modern humans from archaic humans and archaic humans from Homo erectus are unclear. The earliest known fossils of anatomically modern humans such as the Omo remains from 195,000 years ago, Homo sapiens idaltu from 160,000 years ago, Qafzeh remains from 90,000 years ago are recognizably modern humans. However, these early modern humans do possess a number of archaic traits, such as moderate, but not prominent, brow ridges; the emergence of archaic humans is sometimes used as an example of punctuated equilibrium.
This occurs when a species undergoes significant biological evolution within a short period. Subsequently, the species undergoes little change for long periods until the next punctuation; the brain size of archaic humans expanded from 900 cm3 in erectus to 1,300 cm3. Since the peak of human brain size during the archaics, it has begun to decline. Robin Dunbar has argued. Based on his analysis of the relationship between brain size and hominin group size, he concluded that because archaic humans had large brains, they must have lived in groups of over 120 individuals. Dunbar argues that it was not possible for hominins to live in such large groups without using language, otherwise there could be no group cohesion and the group would disintegrate. By comparison, chimpanzees live in smaller groups of up to 50 individuals. Atapuerca Mountains, Sima de los Huesos Saldanha Man Altamura Man Kabwe Skull Steinheim Skull Ndutu cranium Early and Late "Archaic" Homo Sapiens and "Anatomically Modern" Homo Sapiens Origins of Modern Humans: Multiregional or Out of Africa?
Homo sapiens, Museum of Natural History Human Timeline – Smithsonian, National Museum of Natural History
Early human migrations
Early human migrations are the earliest migrations and expansions of archaic and modern humans across continents beginning 2 million years ago with the out of Africa migration of Homo erectus. This initial migration was followed by other archaic humans including H. heidelbergensis, which lived around 500,000 years ago and was the ancestor of both Denisovans and Neanderthals. Early hominids were said to have "crossed land bridges that were covered in water". Within Africa, Homo sapiens dispersed around the time of its speciation 300,000 years ago; the "recent African origin" paradigm suggests that the anatomically modern humans outside of Africa descend from a population of Homo sapiens migrating from East Africa 70,000 years ago and spreading along the southern coast of Asia and to Oceania before 50,000 years ago. Modern humans spread across Europe about 40,000 years ago; the migrating modern human populations are known to have interbred with local varieties of archaic humans, so that contemporary human populations are descended in small part from regional varieties of archaic humans.
After the Last Glacial Maximum, North Eurasian populations migrated to the Americas about 20,000 years ago. Northern Eurasia was peopled in the beginning Holocene. Arctic Canada and Greenland were reached by the Paleo-Eskimo expansion around 4,000 years ago. Polynesia was peopled after 2,000 years ago, by the Austronesian expansion; the earliest humans developed out of australopithecine ancestors after about 3 million years ago, most in Eastern Africa, most in the area of the Kenyan Rift Valley, where the oldest known stone tools were found. Stone tools discovered at the Shangchen site in China and dated to 2.12 million years ago are claimed to be the earliest known evidence of hominins outside Africa, surpassing Dmanisi in Georgia by 300,000 years. Between 3 and 2 million years ago, Homo spread throughout East Africa and to Southern Africa, but not yet to West Africa. Around 1.9 million years ago, Homo erectus migrated out of Africa via the Levantine corridor and Horn of Africa to Eurasia. This migration has been proposed as being related to the operation of the Saharan pump, around 1.9 million years ago.
Homo erectus dispersed throughout most of the Old World. Its distribution is traced by the Oldowan lithic industry, by 1.3 million years ago extending as far north as the 40th parallel. Key sites for this early migration out of Africa are Riwat in Pakistan, Ubeidiya in the Levant and Dmanisi in the Caucasus. China was populated as early as 1.66 Mya based on stone artifacts found in the Nihewan Basin. The archaeological site of Xihoudu in Shanxi Province is the earliest recorded use of fire by Homo erectus, dated 1.27 million years ago. Southeast Asia was reached about 1.7 million years ago. Western Europe was first populated around 1.2 million years ago. Robert G. Bednarik has suggested that Homo erectus may have built rafts and sailed oceans, a theory that has raised some controversy. One million years after its dispersal, H. erectus was diverging into new species. H. erectus is a chronospecies and was never extinct, so that its "late survival" is a matter of taxonomic convention. Late forms of H. erectus are thought to have survived until after about 0.5 million ago to 143,000 years ago at the latest, with derived forms classified as H. antecessor in Europe around 800,000 years ago and H. heidelbergensis in Africa around 600,000 years ago.
H. heidelbergensis in its turn spread across East Africa and to Eurasia, where it gave rise to Neanderthals and Denisovans. H. heidelbergensis and Denisovans expanded north beyond the 50th parallel. It has been suggested that late Neanderthals may have reached the boundary of the Arctic, by c. 32,000 years ago, when they were being displaced from their earlier habitats by H. sapiens, based on 2011 excavations at the site of Byzovaya in the Urals. Other archaic human species are assumed to have spread throughout Africa by this time, although the fossil record is sparse, their presence is assumed based on traces of admixture with modern humans found in the genome of African populations. Homo naledi, discovered in South Africa in 2013 and tentatively dated to about 300,000 years ago, may represent fossil evidence of such an archaic human species. Neanderthals spread across the Near East and Europe, while Denisovans appear to have spread across Central and East Asia and to Southeast Asia and Oceania.
There is evidence that Denisovans interbred with Neanderthals in Central Asia where their habitats overlapped. It is most from an African variety of H. antecessor that H. sapiens developed around 300,000 years ago. Homo sapiens are assumed to have emerged about 300,000 years ago based on thermoluminescence dating of artefacts from Jebel Irhoud, published in 2017; the Omo remains, excavated between 1967 and 1974 in Omo National Park and dated to 200,000 years ago, were long held to be the oldest known fossils of anatomically modern humans. Early modern humans expanded to Western Eurasia, Central and Southern Africa from the time of their emergence. While early expansions to Eurasia appear not to have persisted, expansions to Southern and Central Africa resulted in the deepest temporal divergence in living human populations. Early modern human expansion in sub-Saharan Africa appears to have contributed to the end of late
The Holocene is the current geological epoch. It began 11,650 cal years before present, after the last glacial period, which concluded with the Holocene glacial retreat; the Holocene and the preceding Pleistocene together form the Quaternary period. The Holocene has been identified with the current warm period, known as MIS 1, it is considered by some to be an interglacial period within the Pleistocene Epoch. The Holocene has seen the growth and impacts of the human species worldwide, including all its written history, development of major civilizations, overall significant transition toward urban living in the present. Human impacts on modern-era Earth and its ecosystems may be considered of global significance for future evolution of living species, including synchronous lithospheric evidence, or more hydrospheric and atmospheric evidence of human impacts. In July 2018, the International Union of Geological Sciences split the Holocene epoch into three distinct subsections, Greenlandian and Meghalayan, as proposed by International Commission on Stratigraphy.
The boundary stratotype of Meghalayan is a speleothem in Mawmluh cave in India, the global auxiliary stratotype is an ice core from Mount Logan in Canada. The name Holocene comes from the Ancient Greek words ὅλος and καινός, meaning "entirely recent", it is accepted by the International Commission on Stratigraphy that the Holocene started 11,650 cal years BP. The Subcommission on Quaternary Stratigraphy quotes Gibbard and van Kolfschoten in Gradstein Ogg and Smith in stating the term'Recent' as an alternative to Holocene is invalid and should not be used and observe that the term Flandrian, derived from marine transgression sediments on the Flanders coast of Belgium has been used as a synonym for Holocene by authors who consider the last 10,000 years should have the same stage-status as previous interglacial events and thus be included in the Pleistocene; the International Commission on Stratigraphy, considers the Holocene an epoch following the Pleistocene and the last glacial period. Local names for the last glacial period include the Wisconsinan in North America, the Weichselian in Europe, the Devensian in Britain, the Llanquihue in Chile and the Otiran in New Zealand.
The Holocene can be subdivided into five time intervals, or chronozones, based on climatic fluctuations: Preboreal, Atlantic and Subatlantic. Note: "ka" means "kilo-annum" Before Present, i.e. 1,000 years before 1950 The Blytt–Sernander classification of climatic periods defined by plant remains in peat mosses, is being explored. Geologists working in different regions are studying sea levels, peat bogs and ice core samples by a variety of methods, with a view toward further verifying and refining the Blytt–Sernander sequence, they find a general correspondence across Eurasia and North America, though the method was once thought to be of no interest. The scheme was defined for Northern Europe, but the climate changes were claimed to occur more widely; the periods of the scheme include a few of the final pre-Holocene oscillations of the last glacial period and classify climates of more recent prehistory. Paleontologists have not defined any faunal stages for the Holocene. If subdivision is necessary, periods of human technological development, such as the Mesolithic and Bronze Age, are used.
However, the time periods referenced by these terms vary with the emergence of those technologies in different parts of the world. Climatically, the Holocene may be divided evenly into the Neoglacial periods. According to some scholars, a third division, the Anthropocene, has now begun; the International Commission on Stratigraphy Subcommission on Quaternary Stratigraphy’s working group on the'Anthropocene' note this term is used to denote the present time interval in which many geologically significant conditions and processes have been profoundly altered by human activities. The'Anthropocene' is not a formally defined geological unit. Continental motions due to plate tectonics are less than a kilometre over a span of only 10,000 years. However, ice melt caused world sea levels to rise about 35 m in the early part of the Holocene. In addition, many areas above about 40 degrees north latitude had been depressed by the weight of the Pleistocene glaciers and rose as much as 180 m due to post-glacial rebound over the late Pleistocene and Holocene, are still rising today.
The sea level rise and temporary land depression allowed temporary marine incursions into areas that are now far from the sea. Holocene marine fossils are known, from Vermont and Michigan. Other than higher-latitude temporary marine incursions associated with glacial depression, Holocene fossils are found in lakebed and cave deposits. Holocene marine deposits along low-latitude coastlines are rare because the rise in sea levels during the period exceeds any tectonic uplift of non-glacial origin. Post-glacial rebound in the Scandinavia region resulted in the formation of the Baltic Sea; the region continues to rise, still causing weak earthquakes across Northern Europe. The equivalent event in North America was the rebound of Hudson Bay, as it shrank from its larger, immediate post-glacial Tyrrell Sea phase, to near its present boundaries. Climate has been stable over the Holocene. Ice core