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Reconstructions of 3 species of the Pleistocene bovid genus Pelorovis In the back is P. Sub-Saharan Africa and southern Asia are the only regions that have terrestrial mammals weighing over 1000 kg today.
However, there are indications of a megafaunal extinction events throughout the Pleistocene, particularly in Africa two million years ago, which coincide with key stages of human evolution and climatic trends.
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 very 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.
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, and started to establish continuous, permanent populations in Eurasia and Australasia from 120,000BCE and 63,000 BCE respectively, and the Americas from 22,000 BCE.
Steller's sea cows also 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.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, and the regime shift of previously established faunal relationships and habitats as a consequence.The increased rate of extinction mirrors the sequential pattern of the migration of anatomically modern humans.The further away from Africa, the more recently the area has been inhabited by humans, and the less time the environments (including its megafauna) had had to accustomize to human arrival and vice versa.