Well, from Greenland, because it is such a "new" ice age, we have real records of life under the ice...
Greenland was once carpeted in lush forests, a new study shows.
www.livescience.com
Analysis of two-million-year-old ancient environmental DNA from the Kap København Formation in North Greenland shows there was an open boreal forest with diverse plant and animal species, of which several taxa have not previously been detected at the site, representing an ecosystem that has no...
www.nature.com
Which provide not only evidence of life that can be dated, but also the timing of the Greenland Ice Age's march from north to south, culminating with freezing out the Vikings off the southern tip in the 1400s.
So if we can find and date life under Greenland's ice, WHY CAN'T WE DO THAT WITH NORTH AMERICAN ICE AGE??
Because after 30-50 million years of scraping, nothing is left... 1-2 million years, something is still there...