Introduction

In the ice age, megafauna roamed North America: mammoths, saber-toothed cats, even giant land sloths! What happened to them? In this episode we answer questions about the ice age: What was it? Did birds live during that time period? How about giraffes? Did people live with woolly mammoths? Why did mammoths go extinct? We'll answer your questions with Ross MacPhee, senior curator at the American Museum of Natural History and author of End of Megafauna: The Fate of the World's Hugest, Fiercest, and Strangest Animals. And we'll hear from Nathaniel Kitchel, a Dartmouth researcher who used carbon dating to discover the age of a mammoth rib. Plus, John Moody, of the Winter Center for Indigenous Traditions in Norwich, Vermont, on how mammoths appear in the oral history of the Abenaki people.

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"What was the ice age?" -Karen, 5, Wilmington, Delaware

In the Pleistocene era, which lasted from 120,000 years ago to 15,000 years ago, ice covered the landscape in much of the northern hemisphere. Ice covered all of Canada down into the Northern United States and all of northern Europe. And there were smaller ice sheets in Russia. How did this happen? Scientists think it was a buildup of ice over time.

"The theory is that the winter never ended," explained Ross MacPhee. "You would have snowfalls in the winter and it never really got warm enough to get rid of it completely. The next year that would be built on, built on and built on. And the thing about snow is that it kind of makes its own weather. If you have snow it gets very cold! And that preserves the snow pack for a very long time."

The weight of that snow would compact into ice, eventually covering parts of the world in great sheets of ice. It might help to think of the process as a little bit like what happens when you have a favorite sledding hill: the snow is light and fluffy when you start, but if you sled down it enough times (and walk up the hill, too), eventually the paths get icy from the footsteps and sleds continually packing the snow down.

It wasn't just ice sheets that were a feature of the ice age. All of that water caught up in the ice made sea level drop 300 feet lower than it is now. That exposed lots of land that is now covered in water, including a land bridge connecting Alaska and Russia!

This land bridge allowed a number of species to move into North America from Asia, like bison. And some North American animals went into Asia, like camels and horses! Bear species traveled in both directions. Humans also used the land bridge to migrate into North America, though scientists think some early humans probably used boats too.

Mammoths also migrated over that land bridge! They originated in Asia and came into North America. But there were other species of megafauna that roam the landscape as well, like giant condors, saber toothed cats and even giant sloths.

These species went extinct at the same time as mammoths, as the ice age was ending. Listen to the episode to learn more about the theories of why so many large animals went extinct around the same time.