Cenozoic
Climate

In the Cretaceous, the climate was hot and humid with lush forests at the poles, there was no permanent ice and sea levels were around 300 metres higher than today. This continued for the first 10 million years of the Paleocene, culminating in the Paleocene–Eocene Thermal Maximum about 55.5 million years ago. Around 50 million years ago Earth entered a period of long term cooling. This was mainly due to the collision of India with Eurasia, which caused the rise of the Himalayas: the upraised rocks eroded and reacted with CO in the air, causing a long-term reduction in the proportion of this greenhouse gas in the atmosphere. Around 35 million years ago permanent ice began to build up on Antarctica. The cooling trend continued in the Miocene, with relatively short warmer periods. When South America became attached to North America creating the Isthmus of Panama around 2.8 million years ago, the Arctic region cooled due to the strengthening of the Humboldt and Gulf Stream currents, eventually leading to the glaciations of the Quaternary ice age, the current interglacial of which is the Holocene Epoch.Recent analysis of the geomagnetic reversal frequency, oxygen isotope record, and tectonic plate subduction rate, which are indicators of the changes in the heat flux at the core mantle boundary, climate and plate tectonic activity, shows that all these changes indicate similar rhythms on million years' timescale in the Cenozoic Era occurring with the common fundamental periodicity of ~13 Myr during most of the time. The levels of carbonate ions in the ocean fell over the course of the Cenozoic.
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