Ice age refers to a period in which the kilometres of thick ice on the poles begin to spread and cover more and more of the Earth's surface.

Ice on our planet is more or less uncommon, but once in a while, temperatures on Earth fall low enough, and kilometres of thick glaciers begin to form on its poles. Sometimes, they spread even further and cover more and more of the surface. These periods are called ice ages.¹

Around 55 million years ago, Earth began to cool once again. Continents were sailing towards their current locations, and India began to crash into Asia (50 MYA). The Himalayas started to thrust upwards, and its rainy hills bound more and more warming greenhouse gases from the air.

The South Pole froze first. Antarctica was ripped apart from its closest neighbours (South America and Australia), left alone at the pole, and even isolated by freezing water circulation. The land, once covered with lush forests, soon turned white (35 MYA) – and has been ever since.

Laying in the Arctic Ocean, it took longer for the North Pole to freeze. But slowly, the flowing water became colder and colder, and around 2.6 million years ago, the first glaciers came into being. Unlike the permanent ice sheets in the South, glaciers of the North began to spread and melt, time and again, depending on the movements of the Earth (Milankovitch cycles). Earth entered a peculiar period of recurring ice ages.

The last of these ice ages (this far) began around 120,000 years ago as Earth travelled a bit farther from the Sun. Perhaps being appropriately skewed, too, fewer and fewer sunrays reached our poles. Summers became colder and could no longer melt the ice. Glaciers began to form and spread. Animals such as lions, rhinoceros, hippopotamuses, and elephants had to retreat from the North, yet some, including woolly mammoths, sabre-tooth cats, wolves, and humans, could cope with the surrounding cold.

As more and more water froze, sea levels fell, even a hundred metres, if not more (compared to the current). Because of the low sea levels, Asia became connected to the Americas in the North and almost to Australia in the South, allowing humans (Homo sapiens) to explore new continents, now all the others but Antarctica.

Around 20,000 years ago, give or take a couple thousand years, glaciers reached their peak. Almost a third of our planet was covered in ice and snow, most since the Snowball Earth (635 MYA). By then, Homo sapiens had become the only human species alive, and many ice age animals had been hunted (some blame climate as well) to the brink of extinction, if not all the way there.

Once ice began to melt, land became fertile. Crops started to flourish, and humans gathered near grain fields, domesticating animals, too. The first villages, towns, and cities came into being. It was the dawn of the Agricultural Revolution.

¹ There are many reasons behind ice ages, and whether alone or together, they may begin to cool the Earth. For example, the proportion of warming greenhouse gases, such as carbon dioxide, may decrease in the atmosphere, sometimes withdrawn from the air by heavy rains and stored in the ground for millions upon millions of years. Warm and cold deep ocean currents may shift as continents slowly change their positions. Besides, every now and then, Earth travels a bit farther from the Sun, wobbles and tilts back and forth around its axis (Milankovitch cycles), each altering the amount of sunlight reaching our planet and especially its poles. And once glaciers begin to spread, and the whiter our planet becomes, the more sunrays are reflected back to space, making our world ever colder (albedo effect).

Bibliography

Dartnell, L. 2019. Origins How the Earth Shaped Human History. London, United Kingdom: Penguin Random House. 346 p. ISBN 9781784705435. Pages 31-45, 60, 65-66.

Panciroli, E. 2022. The Earth a Biography of Life The Story of Life On Our Planet Through 47 Incredible Organisms. London, United Kingdom: An Hachette UK company. 255 p. ISBN 9781529413984. Pages 186-187, 224-225, 232-234.

Papagianni D. & Morse, M. A. 2022. The Neanderthals Rediscovered. London, United Kingdom: Thames & Hudson. 238 p. ISBN 9780500296400. Pages 36-39, 105.

Brusatte, S. 2022. The Rise and Reign of the Mammals. London, United Kingdom: Picador. 500 p. ISBN 9781529034233. Pages 333-338.

Frankopan, P. 2023. The Earth Transformed an Untold History. London, United Kingdom: Bloomsbury Publishing. 695 p. ISBN 9781526622563. Pages 34-35.

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