A new study offers evidence that Antartica's Lake Vostok harbors its own unique ecosystem of life forms, despite being buried under two miles of ice for the past 15 million years. This is good news for scientists who are looking for life on other worlds.
It’s hard to imagine how harsh this underground world really is. Lake Vostok is the largest subglacial lake ever discovered and the 7th largest by volume in the entire world. It’s got more than 2 miles (3.7 km) of ice directly above it, immersing it in total darkness.
Consequently, scientists have, for very good reason, speculated that Lake Vostok is a sterile environment and completely devoid of life. The combination of frigid temperatures, heat (from hydrothermal vents), extreme water pressure (on account of all the ice above it), limited nutrients, and total darkness would certainly suggest conditions difficult for even the hardiest organisms.
A few months ago, Russian scientists claimed that the lake contains previously unidentified organisms. The claim was eventually dropped, however, as their samples were found to be contaminated.
But a new study by Bowling Green State University biologist Scott Rogers and his team has offered fresh evidence that the lake is indeed packed with life. Using ice core samples similar to those pulled up by the Russian team, Rogers applied sterilization techniques that prevent contamination. Once the group studied the de-contaminated deep lake samples, they discovered evidence that the Russian scientists had been right about one thing. Lake Vostok appears to contain a complex web of organisms evolved to suit habitats that are uniquely its own.
"Far from sterile"
In total, Rogers' team discovered 3,507 unique genetic sequences in the lake ice. They were able to identify genus and/or species for 1,623 of the sequences. Of these, 94% were linked to bacteria, with the remaining 6% belonging to more complex single-celled organisms, mostly eukaryotes. Two DNA sequences were matched to one-celled archaea.
The researchers were able to identify thousands of bacteria, including some that are typically found in the digestive systems of fish, crustaceans and annelid worms — suggesting (but not proving) that there may be fish and other complex organisms swimming in the lake! Specifically, the sequences hinted at various types of fungi, arthropods, springtails, water fleas, and mollusks. Again, the researchers aren't saying that these organisms exist in the lake — there could be many other explanations for the presence of these bacteria — but this new evidence certainly makes Lake Vostok all the more fascinating and ripe for future research.
Rogers also confirmed the presence of psychrophiles — microbes that love extreme cold — and thermophiles — microbes that thrive in hot water, indicating the presence of hydrothermal vents deep in the lake.
It’s important to note that not all of the DNA and RNA samples were identified. According to NBC science writer Alan Boyle, “The researchers focused on the DNA sequences they could recognize, and not the ones that they couldn't. But that doesn't necessarily mean the unrecognized sequences are exotic forms of life.”
The Lake Vostok story
So an interesting picture is starting to emerge about this remarkable subglacial lake and what’s been going on for the past 35 million years.
It formed from a depression that appeared 60 million years ago when continental plates shifted and cracked. Back then, Antarctica was surrounded by a forested ecosystem. About 34 million years ago, when it was likely a marine bay and still connected to the southern Atlantic ocean, a massive temperature drop covered it in ice. This caused it to descend by about 90 meters, cutting it off from the ocean. A similar event happened 14 million years ago, dropping it yet again.
But prior to it being sealed off from the outside, life could have easily reached the lake by being transported through the atmosphere. And in fact, portions of the lake were ice free about 15 million years ago.
Thus, over the course of the last 15 to 35 million years, life in Lake Vostok may have slowly adapted to the changing conditions — transforming from a terrestrial system to a subglacial system.
Suddenly, an expedition to the ice-covered seas of Jupiter's moon Europa seems all the more worthwhile. If life could adapt to Lake Vostok, maybe it could evolve on Europa, too.