Major geologic events
Scientists have evidence of more than 60 periods of glacial expansion interspersed with briefer intervals of warmer temperatures. The entire Quaternary Period, including the present, is referred to as an ice age due to the presence of at least one permanent ice sheet (Antarctica); however, the Pleistocene Epoch was generally much drier and colder than the present time.
Although glacial advancement varied between continents, about 22,000 years ago, glaciers covered approximately 30 percent of Earth’s surface. Ahead of the glaciers, in areas that are now Europe and North America, there existed vast grasslands known as the “mammoth steppes.” The mammoth steppes had a higher productivity than modern grasslands with greater biomass. The grasses were dense and highly nutritious. Winter snow cover was quite shallow.
These steppes supported enormous herbivores such as mammoth, mastodon, giant bison and woolly rhinoceros, which were well adapted to the cold. These animals were preyed upon by equally large carnivores such as saber toothed cats, cave bears and dire wolves.
The latest glacial retreat began the Holocene Epoch. In Europe and North America the mammoth steppes were largely replaced by forest. This change in climate and food resources began the extinction of the largest herbivores and their predators. However climate change was not the only factor in their demise; a new predator was making itself known.