The Glacial Earth was much different than the one we know today (Source). Mauricio Antón — from Caitlin Sedwick (1 April 2008). “What Killed the Woolly Mammoth?”. PLoS Biology 6 (4): e99. DOI:10.1371/journal.pbio.0060099.

FOSSILS ET AL.

Ice Ages and Early Humans

While estimations vary, we know that our humanlike ancestors first began to appear around two million years ago. This group eventually evolved into the Homo sapiens approximately 300,000 years ago in Eastern Africa.

The exact timing and ordering of migration is contested, but these early humans eventually migrated and spread around the world. Biologists say we are the ultimate “generalist” species meaning we can easily adapt to a wide variety of climates and environments. This talent allowed us to spread as widely as we have, and survive through some dramatic events.

An estimate of human migration time given our current knowledge, ‘kya’ means thousands of years ago. This does not include new potential theories of humans arriving in the Americas much earlier via Polynesia. (Source)

Our ability to survive in different environments is extremely useful because Earth is not a consistent home. Geology and paleoclimate studies have allowed us to peer back in time and see how our planet has changed. Perhaps most famously, we now know that over the past one million years Earth has experienced several ice ages. These occur in somewhat regular patterns every 100,000 years. During an Ice Age, Earth will cool as much as 6 degrees Celsius and be covered by large areas of glaciers.