>I've read that around 20,000 years ago, Chicago was covered by 2 miles of ice.

This is one of the reasons why modern glacial theory is inadequate. Although the evidence does show that a tremendous weight of ice had existed over the Great Lakes, science of the gradual school of thought made the mistake of calculating how long it would take snow to build such a pile of ice just 20,000 years ago.

This is why the Luarentide ice sheet is assumed to have existed for 1 million years. But we know that woolly mammoths and other Pleistocene fossils have been removed from this area and further north dating to 40,000 years ago. If Chicago had two miles of ice just 20,000 years ago, how did the woolly mammoths become buried in the area up to 40,000 years ago?

The ice sheet must advance much more rapidly than current models predict. And it must occur frequently in order for fossils to be found at more or less 11,500 year intervals in the northern latitudes.

Dave