Temperature: 14 °C
Atmospheric oxygen: 20.8%

The Quaternary Period is the current and most recent of the three periods of the Cenozoic Era. It is divided into two epochs: the Pleistocene and the Holocene (which began 11,700 years ago). The Quaternary is typically defined by the cyclic growth and decay of continental ice sheets driven by Milankovitch cycles and the associated climate and environmental changes that occurred. The last expansion of the polar ice sheets took place about 12,000 years ago.


•Horse-shoe crab