Louis Agassiz thought of him self 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 al ways “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 re leased 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. Be cause 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 cre ated a vivid picture of ice ages and proved that they had existed. But it was Yugosla vian physicist Milutin Milankovich, in 1920, who explained why they happened.
Milankovich showed that Earth's orbit is neither circular, nor does it re main 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 sci entists confirmed this theory with research conducted between 2003 and 2005.
