Ice Ages
Year of Discovery: 1837
What Is It? Earth’s past includes periods of radically different climate—
ice ages—than the mild present.
Who Discovered It? Louis Agassiz
Why Is This One of the 100 Greatest?
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.
How Was It Discovered?
Louis Agassiz thought of himself as a field geologist more than as a college professor.
During weeks of rambling hikes through his nat ive 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.
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