How long ago was the Wisconsin glaciation ?
Examples of how life may have affected past climate include : glaciation 2.3 billion years ago triggered by the evolution of oxygenic photosynthesis , glaciation 300 million years ago ushered in by long - term burial of decomposition - resistant detritus of vascular land plants ( forming coal ) , termination of the Paleocene - Eocene Thermal Maximum 55 million years ago by flourishing marine phytoplankton , reversal of global warming 49 million years ago by 800,000 years of arctic azolla blooms , and global cooling over the past 40 million years driven by the expansion of grass - grazer ecosystems .