Earlier claims of similar microbes drawn from a different Antarctic lake, say the study's authors, were controversial because the samples had been contaminated—a problem eliminated in this case by especially careful drilling techniques.

"The report is a landmark for the polar sciences," writes Martyn Tranter, a geochemist at the University of Bristol, England, who was not involved in the study, in a commentary also published in Nature.

It's also a landmark in the science of astrobiology, the search for life on other worlds. In recent years, scientists have come to understand that life can thrive in a much wider range of environments than they once believed, including superheated water at the bottom of the ocean and ice caves in Greenland. That suggests that extraterrestrial life might also exist in places once thought uninhabitable.

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