# Like who came up with the initial idea/ theory and when was it first proven?
In: Planetary Science
I don’t have a lot of specifics, but ice ages (colder periods when ice sheets form further south than they usually do) leave dramatic evidence on the landscape. As time goes on, sheets of ice literally “creep” southwards. Any debris that gets stuck underneath, like rocks and boulders, will get dragged along underneath them. This slowly carves scars into the ground, and the rocks end up very far from where they started once the ice eventually melts. The Great Lakes of North America were actually formed by glaciers cutting basins into the land.
The ice itself also picks up loose dirt, which accumulates. When the ice melts, ridges of dirt remain, and these ridges are called “[drumlins](https://en.m.wikipedia.org/wiki/Drumlin).”
Two other things: ice is *heavy*, and over hundreds to thousands of years the land beneath the ice sheets gets compressed, forming depressions. When the ice melts, the land begins to rebound. We can see this process by looking at how water features like lakes and rivers behaved in the past; lakes will get shallower and shallower as the land decompresses until they’re gone altogether. And speaking of lakes, melting glaciers can form “[glacial lakes](https://en.m.wikipedia.org/wiki/Glacial_lake)” which are *massive* resevoirs. If the glacier itself is holding water in, there is a chance that the resevoir may burst when the ice becomes too thin. The resulting flooding dramatically alters the landscape downstream.
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