This sounds like science fiction, but it actually happened. Researchers who study giant viruses obtained a chunk of permafrost that had been frozen for an estimated 30,000 years. Upon thawing it out, they placed it in with some amoeba. Before long, the giant viruses were bursting from the amoeba.

The culprit turned out to be the largest virus we've ever identified (physically; there are viruses with genomes four times the size). But the permafrost wasn't done with its somewhat creepy gifts, because the same researchers are back with a second giant virus they've pulled from the distant past.

This one is also large, but structured differently from the earlier find. It has a similar sized genome, at 650,000 base pairs long. That's enough to encode 523 genes, about two-thirds of which aren't related to anything we know about. Some of the remainder come from their hosts, others somehow were pulled in from bacteria, and the remainder are very distantly related to genes in other giant viruses.

Because of all these differences, the authors place it in its own genus, Mollivirus, calling it Mollivirus sibericum after its source. The fact that there's been a steady stream of similar discoveries, combined with the distant relationships among them, suggests that we're far from done exploring the diversity of giant viruses. Who knows what we'll find if we thaw out some Canadian permafrost?

PNAS, 2015. DOI: 10.1073/pnas.1510795112 (About DOIs).