00:00 Ice ages are prolonged periods of reduced temperatures during which large continental-sized ice sheets and glaciers form, and there have been at least five ice ages in Earth's history, with the most recent one having a significant impact on human development.

02:07 One early ice age may have been a period known as Snowball Earth, where the entire planet, or at least most of it down to the tropical latitudes, was covered in ice, and evidence for this hypothesis comes from glacial sediment found at tropical latitudes.

03:42 The Quaternary Ice Age, which began 2.58 million years ago and is still ongoing, consists of periods of glaciations and interglacial periods, with the most recent glacial period known as the Wisconsin Glacial Episode.

05:22 Ice ages can be caused by a combination of plate tectonics, changes to the atmosphere, and Milankovic cycles, but there is still debate and theories to explain the discrepancy between the cycles; during the last glaciation, the massive ice sheet on the Northern Hemisphere covered most of Canada, the Midwestern United States, New England, Scandinavia, and Northern Europe, but not the northern part of Asia, most of Alaska, or the southern parts of North America and Europe.

07:04 During the last glaciation, the ice sheets were incredibly thick, deforming the land underneath and causing isostatic rebound, which is still ongoing and causing land to rise and lakes to disappear. Additionally, the glacial maximum resulted in dramatically lower sea levels.

08:48 During the last glaciation, land connections were formed between Indonesia and the Philippines, Australia and Papua New Guinea, the islands in Japan, and Alaska and Siberia via the Bering Land Bridge, which is believed to be the route the first humans took to the Western Hemisphere.

10:21 The most recent ice age has had a significant impact on the development of modern humanity and continues to shape the world today.