Who do you think would win in a fight: a bunch of glaciers, or a bunch of earthworms?

If you went with the hulking ice behemoths over the squashable invertebrates, good guess. And despite the unlikely match-up, this battle actually sort of happened. Some 20,000 years ago, during Earth’s most recent glaciation period, glaciers moved slowly across North America, effectively bulldozing whatever earthworms got in their way. The creatures didn’t become common again until colonists accidentally brought some over from Europe.

The demise, and rise, of the earthworm population is just one of many intriguing facts about ice ages that Mental Floss editor-in-chief Erin McCarthy is covering in this episode of The List Show. When people mention “the ice age,” they’re usually referring to the current—yes, current—one, also known as the Quaternary ice age. But there have been four other ice ages (that we know of), and quite a lot happened during each.

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