Tuesday, November 11, 2008

A Unique Alien Ecosystem

Ecosystems typically have many different kinds of interacting organisms; there are often thousands of different species cooperating and competing for living space and for needed resources. For example, most species that do not have chlorophyll to harvest energy from sunlight must, directly or indirectly, eat other species that can perform that miraculous transformation. Or one species may depend on other species to manufacture or break down specific chemical bonds or provide specific nutrients for food or fuel. In some cases one species depends on another for protection--and gives something in return.

The ecosystems science has studied seem to imply that life can only exist in complex interconnected webs of varied life forms. Very few ecosystems are known that have only a few mutually supportive and competing species. None has ever been found that has only one kind of organism totally cut off from outside biological give and take--not until recently. A bacterium (given the poetic name Candidatus Desulforudis audaxviator*) has been found deep in a South African gold mine. This species has evidently been isolated from other living things and their products for millions of years. It gets its energy from the decay of radioactive uranium in the surrounding rocks, and it has genes to extract raw materials and to produce all the complex carbon and nitrogen chemicals it needs to sustain life.

This, more than any other known organism, could be a key to understanding what kinds of life can flourish on extraterrestrial planets far away from us in the Universe, planets with harsh, isolated environments that we did not previously believe could support living things.

* The name comes from a quotation from Jules Verne's novel Journey to the Center of the Earth. The hero, Professor Lidenbrock, finds a secret inscription in Latin that reads: "Descende, audax viator, et terrestre centrum attinges" (Descend, bold traveler, and you will attain the center of the Earth).