A large and diverse family of hearty rock-eating bacteria and other microorganisms live in a freshwater lake buried a half-mile beneath Antarctic ice, new research confirms.
The finding not only adds another extreme environment where life thrives on Earth, but raises the prospect that similar species could have lived or are still living on Mars.
NASA's ongoing Curiosity rover mission, for example, already has found that the planet most similar to Earth in the solar system once had the chemical constituents needed to support microbial life.
The new research, published in this week's Nature, confirms initial studies 20 years ago that found microbes in refrozen water samples retrieved from Lake Vostok, the largest subglacial Antarctic lake.
Scientists at that time were not on a life-hunting expedition and the indirect sampling process later raised questions about those results.
"People weren't really thinking about ecosystems underneath the ice. The conventional wisdom was that they don't exist, it's a place that's too extreme for this kind of thing," Louisiana State University biologist Brent Christner told Discovery News.
For the new study, Christner and colleagues analyzed samples directly retrieved from another subglacial lake, known as Lake Whillans, which lies beneath about a half-mile of ice on the lower portion of the Whillans Ice Stream in West Antarctica.
The lake is part of an extensive and evolving subglacial drainage network, Christner noted in the Nature paper.
Scientists discovered at least 3,931 microbial species or groups of species in the lake waters, many of which use inorganic compounds as an energy source.
With little surface melt in the area, it is unlikely that water has made its way through the half-mile of ice to reach the lake. Instead, scientists believe the water comes from geothermal heating at the base of the lake and through frictional melting during ice flows.
Any microbes in the water, therefore, most likely survive on energy and nutrients from melting ice, crushed rock, sediment beneath the ice and recycling of materials from dead micro-organisms, glaciologist Martyn Tranter, with the University of Bristol in the United Kingdom, wrote in a related paper in Nature.
"What I find about icy environments on Earth is that, potentially, they are very similar to other icy environments, for example on Mars," Tranter told Discovery News.
"Conditions are right (on Mars) for there to be liquid water at the bed. The right types of rocks are present which contain reduced (compounds) and if there are oxidizing agents present, then microbes can make a living shuttling electrons between reduced compounds and oxidized compounds," he said.
Mars scientist Christopher McKay, with NASA's Ames Research Center in Moffett Field, Calif., isn't convinced.
"I don't like to be unenthusiastic about these results but I don't see much of any implication for Mars or the ice-covered oceans of the outer solar system," McKay wrote in an email to Discovery News.
"First it is clear that the water sampled is from a system that is flowing through ice and out to the ocean. Second, and related to this, the results are not indicative of an ecosystem that is growing in a dark nutrient-limited system. They are consistent with debris from the overlying ice -- known to contain micro-organisms -- flowing though and out to the ocean," McKay said.
"Interesting in its own right, but not a model for an isolated ice-covered ecosystems," he added.
Scientists don't know how long ice sheets have covered Antarctica. "Some folks think that within the last half-million years maybe the West Antarctica ice sheet melted away to not very much," Tranter said.
Since Lake Whillans is at the edge of the West Antarctic ice sheet, sections could have been open to the atmosphere within the last half-million years.
"It's possible that microbes, which are blown everywhere by the wind, were dropped onto a much-reduced West Antarctic ice sheet, since covered by ice, and they've managed to (exist) under the ice every since," Tranter said.
"It's also possible that the type of microbes found in marine sediments ... carry on regardless of whether there is an ice sheet on top of them or not," he added.
Scientists plan additional studies to try to determine how the organisms came to exist in the cold, dark waters beneath Antarctica.