The Pliocene and Early Pleistocene

The Mid-Pleistocene Transition (MPT), also known as the Mid-Pleistocene Revolution (MPR), is a fundamental change in the behaviour of glacial cycles during the Quaternary glaciations. The transition happened approximately 1.25–0.7 million years ago, in the Pleistocene epoch. Before the MPT, the glacial cycles were dominated by a 41,000-year periodicity with low-amplitude, thin ice sheets and a linear relationship to the Milankovitch forcing from axial tilt. After the MPT there have been strongly asymmetric cycles with long-duration cooling of the climate and build-up of thick ice sheets, followed by a fast change from extreme glacial conditions to a warm interglacial. The cycle lengths have varied, with an average length of approximately 100,000 years.

The diagram shows five million years of glacial cycles are shown, based on oxygen isotope ratio believed to be a good proxy of global ice volume. The MPT is the transition between the periodicities shown in green. - Wikipedia - imagepage

Introduction

The next time division down takes us to the 5 million year increment, approximately the average time for a Geological Age (most periods consist of about eight or more ages). So a consideration of the history of complex life on Earth could be covered in terms of about 115 of these such intervals, of which the Plio-Pleistocene (or Plio-Pleisto-Holocene) covered here is just the most recent. Human history, which is only one thousandth of this span, doesn’t even figure at this scale.

The last 5 million years covers the history of the earth during the Pliocene and Pleistocene epochs. This time period is notable for several significant events, including the evolution of Late Tertiary and Quaternary mammals, the appearance of modern plants and invertebrates (or generally only differing at a species level), and the evolution of a number of different hominid species.

For the fanciful equivalent projected into the future, see the medium term far distant future.

The Pliocene lasted from 5.333 million to 2.58 million years ago. It marked the beginning of the transition from a warm, moist climate to the more fluctuating and cooler conditions of the Pleistocene, and saw the first appearances of early human species such as Australopithecus and Homo habilis. This was also the high point of the age of mammals, with many types like modern animals, but only differing at the species level. The illustration here shows some representative types.

A selection of ungulates from the Pliocene of eastern Africa, drawn to scale, showing the rich diversity of late Neogene mammals. Artwork by Mauricio Antón. From left to right: the horse Hipparion cornelianum, the giraffe Giraffa jumae, the bovid Tragelaphus nakuae, the pig Kolpochoerus limnetes, the giraffid Sivatherium maurisium, the bovid Aepyceros melampus, the chalicothere Ancylotherium hennigi, the hippo Hexaprotodon aethiopicus, and the rhino Ceratotherium praecox. These animals lived alongside various species of proboscideans, early hominids, felids, and various other animals in a savannah environment - original page

This epoch featured dramatic climatic changes, which ultimately led to modern species and plants. The Mediterranean Sea dried up for hundreds of thousand years in the Messinian salinity crisis. Along with these major geological events, Africa saw the appearance of Australopithecus which existed in several evolutionary lineages, one of whch would give rise to Homo habilis during the Early Pleistocene. The isthmus of Panama formed, and animals migrated between North and South America, wreaking havoc on the local ecology. Climatic changes brought savannas that are still continuing to spread across the world, Indian monsoons, deserts in East Asia, and the beginnings of the Sahara desert. The Earth's continents and seas moved into their present shapes. The world map has not changed much since, save for changes brought about by the glaciations of the Quaternary, such as the Great Lakes.

The Pleistocene, in turn, was characterized by repeated cycles of glacial and interglacial periods, with alternating ice ages and warmer temperatures, which had a significant impact on the distribution and evolution of life on earth.

Timeline

The last five million years, from Wikipedia

5.332 Mya. Start of Zanclean age (early Pliocene). The Zanclean deluge - a flood theorised to have refilled the Mediterranean Sea 5.33 million years ago. This ended the Messinian salinity crisis and reconnected the Mediterranean Sea to the Atlantic Ocean, although it is possible that even before the flood there were partial connections to the Atlantic Ocean. Evolutionary events (~5 Mya): First tree sloths and hippopotami, diversification of grazing herbivores like zebras and elephants, large carnivorous mammals like lions and the genus Canis, burrowing rodents, kangaroos, birds, and small carnivores, vultures increase in size, decrease in the number of perissodactyl mammals. Extinction of nimravid carnivores. First leopard seals. >
4.8 Mya. Mammoths appear in the fossil record.
4.5 Mya. Marine iguanas diverge from land iguanas.
4 Mya. Australopithecus evolves. Stupendemys appears in the fossil record as the largest freshwater turtle, first modern elephants, giraffes, zebras, lions, rhinoceros and gazelles appear in the fossil record.
3.6 Mya. Piacenzian (Late Pliocene) age beings. Blue whales grow to modern size.
3 Mya. Earliest swordfish.
3.0 to 0.7 Mya. Mammuthus meridionalis (early species of mammoth)
2.7 Mya. Great American Interchange, where various land and freshwater faunas migrated between North and South America. Armadillos, opossums, hummingbirds Phorusrhacids, Ground Sloths, Glyptodonts, and Meridiungulates traveled to North America, while horses, tapirs, saber-toothed cats, jaguars, bears, coaties, ferrets, otters, skunks and deer entered South America. Paranthropus evolves in Africa.
2.588 Mya. Magnetic pole reversal, start of Matuyama chron. Marks the beginnng of the Gelasian age. This was originally Late Pliocene but was moved to the Early Pleistocene. It is equivalent to the European Villifranchian land mammal age, a sort of Plio-Pleistocene transition period. The earliest Stone Tools (~2.6 Mya.) also date from around this time. The development of stone tool technology marks the beginning of the Paleolithic era and the earliest evidence of human activity.
2.5 Mya. Earliest species of Smilodon.
2 Mya. First members of genus Homo, Homo habilis, appear in the fossil record. Diversification of conifers in high latitudes. The eventual ancestor of cattle, aurochs (Bos primigenus) evolves in India.
1.8 Mya. Calabrian age (Early Pleistocene) begins
1.7 Mya. Australopithecines go extinct.
1.6 Mya. Origin of Homo erectus. This species is considered to be the first human species to leave Africa and migrate across the world.
1.4 to 0.9 Mya. Early illinoian / gunz glacial
1.25 Mya. Start of Mid-Pleistocene Transition
1.2 Mya. Evolution of Homo antecessor. The last members of Paranthropus die out.
1 Mya. First coyotes.
800 Kya. Short-faced bears (Arctodus simus) become common in North America. Hominid discovery of Fire: The ability to control fire marked a major turning point in human evolution and provided warmth, light, and a means of cooking food.
781 ± 5 Ka Kya. last magnetic pole reversal, start of Brunhes chron (current magnetic polarity), ice age and global drying, possibly colder and drier than the late Miocene (Messinian) through early Pliocene (Zanclean) cold period.
770 kya. Middle Pleistocene (Chibanian age) begins, the start of the Ice Age proper and completion of Mid-Pleistocene transition.
700 to 500 Ka. Steppe mammoth (M. trogontherii).
600 Kya. Evolution of Homo heidelbergensis.

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