Published online 9 December 2002 | Nature | doi:10.1038/news021209-1

News

Goldmine yields clues for life on Mars

Radioactive bacteria live deep in the Earth - and maybe elsewhere.

Mine dwelling bacteria may be similar to the first life on EarthMine dwelling bacteria may be similar to the first life on Earth© GettyImages

There are tiny creatures living off radiation in ancient pockets of water several kilometres beneath the Earth's surface, say researchers.

The microbes seem to have been isolated for hundreds of millions of years. Similar conditions might exist beneath the surface of Mars.

"Anywhere you have a crust with uranium and water in it, you have the potential for life," microbiologist Tullis Onstott, of Princeton University, New Jersey, told this week's American Geophysical Union in San Francisco.

As you go deeper, the chemicals essential for normal life - organic matter and oxygen - disappear. And you get crushed and cooked, as temperature and pressure rise.

Microbes have been found a kilometre or so beneath the Earth's surface before. But cost and contamination with shallower bugs have hindered scientists looking deeper for life.

Working with miners in the world's deepest holes - 3.5 kilometre-deep South African goldmines - Onstott and his colleagues found hot water rich in bacteria.

The water is loaded with dissolved hydrogen gas, at a concentration up to a hundred million times higher than normal. Radioactive isotopes in the water show that the gas could only have formed by radioactive energy from surrounding uranium deposits splitting the water into hydrogen and oxygen, argues Onstott.

Researchers had speculated that bacteria might make hydrogen in this way, but it has never been seen before. "It's a completely novel system for supporting life," says John Baross, who studies deep-sea bacteria at the University of Washington in Seattle.

The mine-dwelling bacteria are hard to grow in the lab. Genetic evidence suggests that some of the microbes are related to a species called Pyrococcus abyssi, which lives in hot, deep-sea vents.

“>It's a completely novel system for supporting life”

John Baross
University of Washington

These bacteria are thought to be similar to the first life on Earth. They use hydrogen and sulphur to survive without oxygen.

Other genetic sequences of microbes in the mine water are unlike those of any other species. Onstott says that he would not be surprised if the mine contained new species with new types of metabolism.

Radioactive dating by Onstott's colleagues suggests that some pockets of mine water have been isolated for several hundred million years. "The dinosaurs came and went while this water has been down there," he says.

If the microbes can be grown and their workings probed, they should provide new insights into primitive life, Baross adds.

Missions to Mars could look for life by sniffing for hydrogen seeping up from deep in the planet's crust, says Onstott. Mars has some water and uranium, although less than Earth. 

University of Washington