What Was the Ice Age?

What Was the Ice Age?
 
Southwest France, September 1940
 
Eighteen-year-old Marcel Ravidat is exploring the forest outside his village with three friends. People say there is a secret underground passage in these woods that leads to a nearby castle.
 
The four teenagers spot a small opening in the ground. Could this be the way to the castle . . . or to buried treasure?
 
Marcel is the first to lower himself into the dark. The fifty-foot passage is long and narrow. Marcel is terrified. When he reaches the bottom, he sees that he is inside an enormous cave. But it is too dark to see much else.
 
So Marcel climbs back up. The next day he returns to the cave with his friends. This time he has a grease gun to use as a torch.
 
Back in the cave, what the boys see amazes them. All over the curving cave walls are hundreds of colorful paintings of prehistoric beasts. The animals almost seem to come to life in the flickering light!
 
Sixty horses gallop along the cave walls. Red deer swim across a river. Shaggy-haired rhinos thrust their sharp horns in the air. Some of these paintings are huge. One of a giant ox measures eighteen feet across!
 
A lone human figure, wearing a bird mask, appears on the wall. He is being charged by a bison. The animal is injured. A spear is stuck in  its belly. Its guts are spilling out!
 
The boys can’t believe their eyes. They are gazing at scenes from a long-lost world. What they’ve discovered is far more interesting than some old castle.
 
Today scientists know that these cave walls at Lascaux (say: law-SKO) were painted by humans living 17,000 years ago. These artists lived during a very cold period of Earth’s history: the Ice Age.
 
During the Ice Age, great sheets of ice covered much of Europe, Asia, and North America. People took shelter in caves for warmth. (That is where the term caveman came from.) Animals like bears, lions, and hyenas also lived in caves, so house hunting was a deadly affair!
 
People’s chances of staying alive depended on their ability to adapt—to learn how to survive in a world of fearsome predators and wild weather.
 
The Ice Age was certainly a difficult and dangerous time to be alive.
 
 
Chapter 1: An Ice-Covered World
 

Less than two hundred years ago, no one knew there had been an Ice Age. Then in 1837, a young Swiss professor named Louis Agassiz (say: LOO-ee AG-uh-see) gave a speech to a group of scientists. What he told the audience shocked them.
 
Europe—and much of the world, he said—was once completely covered in ice! He said that this sheet of ice stretched from the North Pole to the Mediterranean Sea. The whole European continent was frozen beneath it.
 
This age of ice was so cold, Louis said, it wiped out all life on Earth. In his book Studies on Glaciers, Louis said that “springs dried up, streams ceased to flow, and the rays of the sun, rising over this frozen shore . . . were greeted only by the whistling of the northern wind . . . across the surface of the huge ocean of ice.”
 
Louis was right. Mostly.
 
The ice hadn’t reached as far as the Mediterranean. And many creatures—humans among them—did survive the Ice Age. But Louis was on the right track.
 
How’d he come up with this idea?
 
Believe it or not, it was by looking at some rocks.
 
Louis went to the Alps in the summer of 1836. The Alps are tall mountains in central Europe. So tall, there are always glaciers—large bodies of ice—on their mountaintops.
 
Louis Agassiz stayed at the home of Jean de Charpentier (say: ZHON duh Shar-pahn-tee-AY). Jean was a geologist, someone who studies rocks to learn about Earth’s past.
 
One day, Jean pointed out some boulders in the mountains. (Boulders are very large rocks.) The boulders didn’t look like they had come off the mountains that surrounded them. They seemed to be made of a different kind of rock.
 
Jean told Louis he knew why this was. Glaciers had put them there, Jean said. Long ago, when the mountain glaciers were growing, they picked up the boulders from someplace else. The moving ice dragged the boulders along. This made deep scratches in the mountainsides. Jean showed these marks to Louis, too.
 
In time, as the ice melted away and the glaciers became smaller, the boulders stayed where the glaciers had dropped them.
 
Louis had seen boulders like these before, standing alone in fields. He had never paid them much attention. However, when Louis returned home from his trip to Jean’s, he began to notice boulders all around him.
 
Louis was sure Jean was right. These boulders were proof that glaciers had once covered the area.
 
But Louis took things one step further. If glaciers were once bigger in the Alps, couldn’t they have been bigger around the rest of the world, too? The next year, Louis gave his famous Ice Age speech.
 
What did Jean think about all of this? He was surprised. Jean didn’t think Louis had the proof for these new ideas.
 
For other people, it wasn’t a matter of science. The notion of an Ice Age went against their belief in God and the Bible. The boulders weren’t moved by an ancient ice sheet, they said. The boulders were carried by water. Water from a powerful flood that had covered the earth 5,000 years before. The story of this flood was told in the Bible.
 
Louis disagreed. The boulders were way too heavy to be moved by water. It had to be ice, he said!
 
Talk of the Ice Age spread across Europe. In England, there was a great interest in geology. Thousands of people—not just scientists—gathered in university halls to hear geologists speak about their discoveries.
 
The best part of geology was that almost anyone could contribute to the science. They just had to go out in the country, write about what they saw, and collect samples. Louis always had encouraged his students to “study nature, not books.”
 
So that was what ordinary people started doing, too! And what they saw was more proof of an Ice Age. Scratch marks on mountainsides. Huge rocks standing in fields, as if dropped by giants. Smooth sheets of rock, polished by the moving ice. Rocks, pebbles, and other debris (called glacial drift) where glaciers had stopped growing and begun to melt.
 
They drew maps with this information. Forty years after Louis’s speech, a world map of Ice Age glaciers had been pieced together. It showed that places like Seattle, Washington, and New York City were once under ice!
 
Though it had taken years, the world was beginning to believe Louis Agassiz!
 
Of course, simply knowing that there had been an Ice Age didn’t explain what had caused the world to cool. Nor was there any understanding of when the Ice Age began. Or how long it lasted. Nevertheless, the rush to unlock the Ice Age’s secrets had begun.