A giant lake buried more than two miles beneath the Antarctic ice has been found to contain a "surprising" variety of life.
Analysis of ice cores obtained from the basin of Lake Vostok, the subglacial lake that Russian scientists drilled down to in 2012, have revealed DNA from an estimated 3,507 organisms.
While the majority were found to be bacteria, many of which were new to science, there were also other single celled organisms and multicellular organisms found, including from fungi.
The diversity of life from the lake has surprised scientists as many had thought the lake would be sterile due to the extreme conditions.
Lake Vostok was first covered by ice more than 15 million years ago and is now buried 12,000 feet beneath the surface, creating huge pressures. Few nutrients were expected to be found.
However, samples of ice that had formed as water from the lake froze onto the bottom of the glacial ice sheet above have revealed it is teeming with life.
This will raise hopes that life may be found in other extreme environments on other planets. One of Jupiter's moons, Europa, for example, is covered with an icy shell that may hide a liquid ocean below where life could exist.
Dr Scott Rogers, a biologist at Bowling Green State University, in Ohio, and led the DNA analysis of biological material found in the ice cores, said: "We found much more complexity than anyone thought.
"It really shows the tenacity of life, and how organisms can survive in places where a couple dozen years ago we thought nothing could survive.
"The bounds on what is habitable and what is not are changing."
Lake Vostok is around 160 miles long and 30 miles wide, covering an area of more than 6,000 square miles beneath the Antarctic ice sheet.
Among the bacteria found in the samples brought to the surface were those commonly found in the digestive systems of fish, crustaceans and annelid worms, raising the prospect there could be more complex life still living in the lake.
Isolated from the rest of the world for 15 million years, some of the DNA sequences were found to be unique to science and may belong to new species that have evolved in the depths.
Writing in the journal PLOS One, Dr Rogers and his colleagues said: "The sequences suggest that a complex environment might exist in Lake Vostok.
"Sequences indicating organisms from aquatic, marine, sediment and icy environments were present in the accretion ice.
"In addition, another major proportion of the sequences were from organisms that are symbionts of animals and/or plants.
"Over 35 million years ago, Lake Vostok was open to the atmosphere and was surrounded by a forested ecosystem. At that time, the lake, which might have been a marine bay, probably contained a complex network of organisms.
"As recently as 15 million years ago, portions of the lake were ice free at least part of the time. During these times, organisms were likely being deposited in the lake.
"While the current conditions are different than earlier in its history, the lake seems to have maintained a surprisingly diverse community of organisms.
"These organisms may have slowly adapted to the changing conditions in Lake Vostok during the past 15–35 million years as the lake converted from a terrestrial system to a subglacial system."
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