Old Cold: Living in Ice Age America


Back Off, Brachiosaurus. Take a Hike, T. Rex.

Make way for the giant mammals of the Ice Age. That's right. A whole new variety of animals developed after the dinosaurs went extinct 65 million years ago. By 3 million years ago, furry elephants and supersized sloths roamed the land.

Oh, Give Me a Home…

What was North America like when giant beasts were at home on the range? Most of it was very different than the place we know now. Ever been to Chicago in the winter? Not cold enough. How about a blizzard in North Dakota? You're getting warmer, er, colder. Antarctica? That's it! There aren't too many places in the world today that resemble North America during the last great Ice Age.

The Earth is ancient. Scientists estimate that it is about 4.6 billion years old. Over all those years, the climate on Earth has changed back and forth between warm and cold. At times, the Earth has been a tropical, humid place. But now and again, the Earth turned cold and wrapped itself in sheets of ice. These cycles of warm and cold take millions of years. They are caused by changes in the way the Earth orbits the sun and how it tilts on its axis, which affect how much of the sun's heat reaches the Earth. The last great cold cycle, which we know as the Ice Age, ended about 10,000 years ago.

During the Ice Age, the Earth's average temperature was about 12 degrees Fahrenheit colder than it is today. That was enough to keep snow from melting during the summers in northern regions. As snow fell on snow, thick sheets of ice called glaciers formed. Their tremendous weight began to push them 200 to 400 feet southward each year until ice covered 17 million square miles of what is now Europe, North and South America, Antarctica, and Asia. Smaller glaciers even formed on mountaintops in Hawaii and Africa. Icebergs filled half the world's oceans. Imagine ice covering nearly everything in North America north of St. Louis—and not just ordinary ice, either. The huge glaciers were up to two miles thick, and they weighed enough to gouge out the Great Lakes, move huge boulders, and scrape and scratch rocks with marks we can still see. Today, only Greenland and Antarctica remain covered with ice; smaller glaciers ebb and flow in the high mountain ranges, but they are mere shadows of the huge ice sheets of 20,000 years ago.

Where the Sabertooth Tiger and the Giant Short–Faced Bear Roam

Nothing could live on these ice sheets, of course, but just beyond their reach the land teemed with life. In the colder weather of the Ice Age, enough seawater froze that sea levels were lower by about 300 feet, revealing landmasses unknown today. An entire subcontinent, called Beringia, surfaced and connected Alaska and Russia. Since the melting of the glaciers, much of this frozen land, a thousand miles wide and twice the size of Texas, has been again covered with water. But during the Ice Age, Beringia, though cold, remained remarkably ice-free. No forests or even trees grew there, but grasses and edible plants supported an amazing array of now extinct beasts, including American lions, giant short-faced bears, and wild horses. They used Beringia as a way to cross from Asia into North America, probably searching for new sources of food.

…And the Mammoth and Mastodon Play

But the undisputed king (or queen) of Beringia was the woolly mammoth. This Ice Age creature and the modern elephant share an ancient ancestor, and in many ways they are alike. Both are huge, both have a trunk and tusks, and both are vegetarians. Unlike its hot-weather cousin, however, the woolly mammoth was well adapted to the cold world in which it lived. Four layers insulated the mammoth against temperatures as low as −50 degrees Fahrenheit. Beneath its one-inch-thick skin lay several inches of fat. A dense layer of wool covered the skin, and on top of it all, thick “guard hairs” up to three feet long gave the woolly mammoth its warm and fuzzy look. Its small ears and short trunk lost little body heat. (By contrast, in the heat of Africa and India, modern elephants use their large ears to release heat from their bodies.) Keeping warm takes fuel, and the mammoth ate up to 400 pounds of grass and plants each day, using its curved tusks to push the snow away. During the long, dark winters, when food was scarce, the mammoth had enough body fat to sustain it.

Other varieties of mammoth roamed North America, including the gigantic Columbian mammoth, which lived well south of the ice. The mastodon, another elephant-like creature, ranged all over, from Florida to Washington state.

So what happened to these beasts? At the end of the Ice Age, in a mere 2,000 years, nearly 70 species went extinct. Some scientists think that, as the glaciers melted, the good grazing lands grew wet and forests began to take over the land, making it difficult for the large animals to find food. Other scientists believe that disease may have killed off the big mammals.

Another Ice Age Animal

There is one other theory about the extinction of the Ice Age creatures. Human beings, too, crossed the Beringia land bridge into North America, probably around 12,000 years ago, late in the Ice Age. They gradually spread southward along ice-free pathways. How did humans survive the cold? One way was to hunt and kill the large animals for their meat, fur, bones, and hides. Ice Age humans even made needles out of bone and, using sinew for thread, sewed warm clothes together from animal skins. Archaeologists call these early people the Clovis, and they have found Clovis spearheads alongside the remains of mammoths and mastodons. But could humans have wiped out entire species by hunting, or “overkilling”? Perhaps a changing climate weakened the animals enough to make them easy prey for human hunters. But evidence is scant, and experts disagree about the role humans played in the disappearance of the Ice Age giants.

Want to catch a glimpse of the Ice Age? Check out the muskoxen and caribou at your local zoo. Unlike most other Ice Age beasts, these sturdy creatures still wander the snowy, cold reaches of the far north. The muskox wears a fur coat similar to that of the mammoth, and its impressive horns give it a distinctly ancient look. Oh, and just in case you think ALL the Ice Age animals were giants, meet the tiny pika, a furry mouselike creature that has always made its home on the lonely mountaintops that poke through the glaciers. It survived the Ice Age (and thousands of winters since) by storing grasses to eat among the rock piles that sheltered it against the blustery cold.

Not all of North America was covered in ice during the Ice Age. In Florida, for instance, the climate was a lot like it is today—tropical and hot. The southwestern part of the continent also provided refuge for creatures that preferred warmer weather. Some of these animals were pretty bizarre, even by Ice Age standards. The glyptodon, for example, looked like nothing alive today. This 8-foot-long mammal had teeth like a mouse and a furry face, but its body was protected by a hard turtlelike shell. A little armored cap and a tail sheathed in an armored tube were further protection against predators such as sabertooth tigers. Though the glyptodon was as big as a modern-day car, it was probably a gentle giant. It ate only plants.

Baby Dima

How do we know so much about mammoths and other extinct Ice Age creatures? Dinosaur remains are rare finds, but the bones of Ice Age beasts are relatively plentiful. Many animals were lured to lush waterholes, where they became trapped in gooey mud or tar and died of starvation or exhaustion. Their skeletons, which have been recovered and put back together, tell us everything from how these animals moved to when they lived and how old they were when they died. People once thought that giant tusks poking through the ice were evidence of fearsome underground beasts. But, for scientists, mammoth remains preserved in the frozen ground provide a wealth of information. In parts of Siberia, the ground is frozen to 1,500 feet below the surface. This permafrost can preserve a mammoth's body for tens of thousands of years, until shifting Earth reveals its hiding place. Baby Dima, a mammoth calf discovered in 1977, is one of the best-preserved examples. His body and skin were intact, and tufts of hair still clung to his back legs. Scientists could even take samples of his blood and look inside his stomach.

Vocabulary

refuge:
Protection or shelter from danger or trouble.
scant:
Not enough in amount or size.
subcontinent:
A large area of land, such as India, that is part of a continent but is considered a separate geographical or political division.

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Activity

  1. Why would a change in Earth's orbit or the tilt of Earth on its axis affect Earth's climate?
    Answer: A change in Earth's orbit or in the tilt of Earth on its axis affects how much sunlight reaches Earth.
  2. During the last Ice Age, Earth was about 12 degrees Fahrenheit colder than it is today. The temperature in your town or city might change 12 degrees from one day to the next. Why do you think Earth's climate was so affected by the cooler temperature of the last Ice Age? Write a few sentences to explain your answer.
    Answer: Answers will vary but could include that because Earth was 12 degrees colder, much of the ice that thaws during the summer months today stayed frozen during the Ice Age. The ice and glaciers built up over time, and as they moved, they scraped out valleys in the Earth.
  3. What possible effect might there be on the planet if the temperature were an average of 12 degrees warmer than it is today?
    Answer: Answers will vary but could include that all the ice at the poles would melt and raise the sea level. Summers would become much hotter. It might be difficult to farm in certain areas.

Activity

  1. Why would a change in Earth's orbit or the tilt of Earth on its axis affect Earth's climate?
    Answer: A change in Earth's orbit or in the tilt of Earth on its axis affects how much sunlight reaches Earth.
  2. During the last Ice Age, Earth was about 12 degrees Fahrenheit colder than it is today. The temperature in your town or city might change 12 degrees from one day to the next. Why do you think Earth's climate was so affected by the cooler temperature of the last Ice Age? Write a few sentences to explain your answer.
    Answer: Answers will vary but could include that because Earth was 12 degrees colder, much of the ice that thaws during the summer months today stayed frozen during the Ice Age. The ice and glaciers built up over time, and as they moved, they scraped out valleys in the Earth.
  3. What possible effect might there be on the planet if the temperature were an average of 12 degrees warmer than it is today?
    Answer: Answers will vary but could include that all the ice at the poles would melt and raise the sea level. Summers would become much hotter. It might be difficult to farm in certain areas.