That map was supposed to be erased after the continent specific ice age theory surfaced. The Warmers do not like it at all, for obvious reasons...
So they erased all online references to NORTH AMERICAN ICE AGE
except the MAPS and that MAP says the ice way south of Chicago dates back to 50 million years, which is likely correct... putting Chicago under ice for 50, not 30, million years
as the LINE OF WHERE THE GLACIERS MELTED MOVED "NORTH" on a TECTONIC PLATE MOVING SW....
and that line ended in Chicago.
What ended the NA ICE AGE?
When the "water" between Ellesmere Island and the rest of Canada changed from glacier to water. When did that happen? In the past 5 million years for sure, perhaps sooner. But that event TURNED OFF THE EARTH GLACIER MANUFACTURING SYSTEM except on the new Ellesmere "Island," which was not an island 50 million years ago.