Previous | Next

The Pliocene and Early Pleistocene

The Mid-Pleistocene Transition
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


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.

Ungulates from the Pliocene of eastern Africa
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.


The last five million years, from Wikipedia

Previous | Next

Home | Big History

Page by M Alan Kazlev, 2023