Yes... the tv show touched on that as well. One hypothesis says that life may have started on Earth much earlier than thought. Although surface life would be destroyed every time there was a large impact, life underground would survive to repopulate the surface once it became habitable again. This may have happened several times.

I'm reminded of the bacteria found in the rocks 2-1/2 miles underground in the gold mines of South Africa.

Gotta love those extremophiles.

Brian