The Quaternary Period is the geologic time period from the end of the Pliocene Epoch roughly 1.8-1.6 million years ago to the present. The Quaternary includes 2 geologic subdivisions -- the Pleistocene and the Holocene Epochs.
In a recent revision of the international classification of geological time periods, the Quaternary was subsumed into the Neogene. The move has met with some resistance from geologists.
The 1.8-1.6 million years of the Quaternary represents the time during which recognizable humans existed. Over this short a time period, the total amount of Continental drift was less than 100 km, which is largely irrelevant to paleontology. The major geographical changes during this time period included periodic closing of the Strait of Gibraltar and the subsequent evaporation of the Mediterranean Sea, followed by the breach and flooding of that sea; the periodic closings of the Strait of Bosphorus and Skaggerak, which respectively turned the Black Sea and Baltic Sea into fresh water, followed by their breaches which flooded the former and drained the latter; the periodic filling of the English Channel, forming a land bridge between Britain and Europe; the periodic closing of the Bering Strait, forming the land bridge between Asia and North America; and the periodic flash flooding of Scablands of the American Northwest by glacial water. The Great Lakes and other major lakes of Canada, and Hudson's Bay, are also just the results of the last cycle, and are temporary. Following every other Ice age within the Quaternary, there was a different pattern of lakes and bays.
The Climate was one of periodic glaciations with continental glaciers moving as far from the poles as 40 degrees Latitude. Few major new animals evolved, again presumably because of the short-in geologic terms-duration of the period. There was a major extinction of large mammals in Northern areas at the end of the Pleistocene Epoch.
Many forms such as saber-toothed cats, mammoths, mastodons, glyptodonts, etc., became extinct worldwide. Others, including horses, camels and cheetahs became extinct in North America.
In time, thanks to the refinement of geology, it was verified that there were several periods of forward and backward movement of the glaciers and that past temperatures on Earth were very different from today. In particular, the Milankovitch cycles of Milutin Milankovitch are based on the premise that variations in incoming Solar radiation are a fundamental factor controlling Earth's climate.
| Tertiary sub-era | Quaternary sub-era | |||
|---|---|---|---|---|
| Neogene period | ||||
| Miocene | Pliocene | Pleistocene | Holocene | |
| Aquitanian | Burdigalian | Zanclean | Early | |
| Langhian | Serravallian | Piacenzian | Middle | |
| Tortonian | Messinian | Gelasian | Late | |