12/04/2023
Quaternary Period
Mean 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.
The Quaternary is a period of the repeating glaciations, which are defined by the previously mentioned Milankovitch cycles. The angle of Earth’s axial tilt with respect to the orbital plane varies between 22.1 and 24.5 degrees over a cycle of about 41,000 years. The current tilt is 23.44 degrees, roughly halfway between its extreme values. Increased tilt increases the amplitude of the seasonal cycle, providing more solar radiation in each hemisphere’s summer and less in winter – in other words, climate at higher latitudes becomes warmer and stops glaciation. The tilt last reached its maximum 10,700 years ago and now is in the decreasing phase of its cycle and will reach its minimum in 9,800 years. The current trend of decreasing tilt will promote milder seasons, as well as an overall cooling trend.
The Quaternary is the modern period, and it represents our current fauna and flora. However, periodic glaciations had a huge impact on the terrestrial biota, frequently destroying plant and animal species. After the last ice age, many large Pleistocene mammals such as saber-tooth cats, mammoths, and mastodons became extinct worldwide.