It was a revolutionary idea: Earth’s climate had not always been the same. Every scientist for thousands of years had assumed that Earth’s climate had remained unchanging for all time.
Then Louis Agassiz discovered proof that all Europe had once been covered by crushing glaciers. Earth’s climate had not always been as it was now. With that discovery, Agassiz established the concept of an ever-changing Earth.
This discovery explained a number of biological puzzles that had confounded scientists for centuries. Agassiz was also the first scientist to record careful and extensive field data to support and establish a new theory. Agassiz’s work did much to begin the field of geology and our modern view of our planet’s history.
Louis Agassiz thought of himself as a field geologist more than as a college professor. During weeks of rambling hikes through his native Swiss Alps in the late 1820s he noticed several physical features around the front faces of Swiss valley glaciers. First, glaciers wormed their way down valleys that were “U” shaped, with flat valley bottoms. River valleys were always “V” shaped. At first he thought that glaciers naturally formed in such valleys. Soon he realized that the glaciers, themselves, carved valleys in this characteristic “U” shape.
Next he noticed horizontal gouges and scratches in the rock walls of these glacier valleys, often a mile or more in front of the actual glacier. Finally, he became aware that many of these valleys featured large boulders and rock piles resting in the lower end of the valley where no known force or process could have deposited them.
Soon Agassiz realized that the mountain glaciers he studied must have been much bigger and longer in the past and that they, in some distant past, had gouged out the valleys, carried the rocks that scored the valleys’ rock walls leaving claw-mark scratches, and deposited giant boulders at their ancient heads.
In the early 1830s Agassiz toured England and the northern European lowlands. Here, too, he found “U”-shaped valleys, horizontal gouges, and scratch marks in valley rock walls, and giant boulders mysteriously perched in the lower valley reaches.
It looked like the signature of glaciers he had come to know from his Swiss studies. But there were no glaciers for hundreds of miles in any direction. By 1835, the awe-inspiring truth hit him. In some past age, all Europe must have been covered by giant glaciers. The past must have been radically different than the present. Climate was not always the same.
In order to claim such a revolutionary idea, he had to prove it. Agassiz and several hired assistants spent two years surveying Alpine glaciers and documenting the presence of the telltale signs of past glaciers.
When Agassiz released his findings in 1837, geologists worldwide were awed. Never before had a researcher gathered such extensive and detailed field data to support a new theory. Because of the quality of his field data, Agassiz’s conclusions were immediately accepted, even though they radically changed all existing theories of Earth’s past.
Agassiz created a vivid picture of ice ages and proved that they had existed. But it was Yugoslavian physicist Milutin Milankovich, in 1920, who explained why they happened. Milankovich showed that Earth’s orbit is neither circular, nor does it remain the same year after year and century after century. He proved that Earth’s orbit oscillates between being more elongated and being more circular on a 40,000-year cycle. When its orbit pulled the earth a little farther away from the sun in winter, ice ages happened. NASA scientists confirmed this theory with research conducted between 2003 and 2005.
During the last ice age the North American glacier spread south to where St. Louis now sits and was over a mile thick over Minnesota and the Dakotas. So much ice was locked into these vast glaciers that sea level was almost 500 feet lower than it is today.