Two groups of scientists report finding life hidden in extremely unusual conditions beneath the surface of the Earth. This suggests that similar life forms might be lurking in comparable habitats on Mars or elsewhere in the solar system.
Thriving in a bubbling hot spring 200 meters underground in the Western U.S. state of Idaho are colonies of microbes unlike anything discovered before. Far out of the reach of the sun, they get their energy from hydrogen in rocks.
Meanwhile, microbes are surviving at minus 30 degrees Celsius in very salty arid soil three to six centimeters beneath the surface of Antarctica's ice-free Dry Valleys. That is deeper than any living organisms found on that continent. The extremely high salinity prevents the soil from freezing.
One of the scientists involved in the Antarctic study, Victor Baker of the University of Arizona, says both discoveries hint that such organisms might once have been the rule rather than the exception.
"It is becoming very probably that the origins of life were not in some warm little pond on the edge of the ocean, as Darwin hypothesized 150 years ago," he said. "But rather that the complex chemical reactions on interfaces where things like hydrogen are in abundance may have been the places where life first started."
As evidence, Mr. Baker and his colleagues say the fungi they discovered surviving in the frigid Antarctic soil are among Earth's most primitive organisms.
Likewise, the Idaho hot springs discovery reported in the journal Nature is of a one-celled microbe called Archaea, a relative of bacteria believed similar to some of the first life forms on Earth.
But the U.S. Geological Survey researcher who plumbed the Idaho springs, Francis Chapelle, says that the life forms are not so interesting as their location.
"The actual micro-organisms are not unique. What is unique is the ecosystem," he said. "That is analogous to the kinds of microbial systems that could have evolved on the early Earth and which have been hypothesized to occur on Mars and places like Europa."
Europa is one of Jupiter's four major moons. It and Mars are not hospitable places for humans, but the new research suggests that they could be very comfortable for microbes like the ones found in Idaho and Antarctica.
"The interesting thing is that the landscape there in the Antarctic is very similar to what we see in places on Mars," said James Dohm, a University of Arizona geologist who participated in the unique Antarctica fungus find. "Finding life in these very extreme environments gives the possibility of potentially finding life on Mars."
The discovery of the microbes in the harsh Idaho and Antarctic habitats are only the latest of several similar finds over the years. Scientists previously found algae, fungi, and bacteria growing inside porous sandstone and surface pavement in Antarctica's Dry Valleys more than 20 years ago. Scientists have since found long-lived algae submerged under 16-meter-thick Antarctic lake ice crust and bacteria living in cracks through which hot volcanic gas escapes.
The University of Arizona's Victor Baker says the newest findings in Idaho and Antarctica could suggest similar places on Mars where future U.S. robotic landers would search for evidence of life.
"The results are, of course, only suggestive," he said. "These things have not been proven for Mars yet. But I think they open up some broader possibilities for the type of experiments that would be on landers and also very important in the interpretation in the features that might be remotely sensed from orbit."
In view of the discoveries, some researchers say the question should not be whether life ever existed elsewhere in the solar system but whether it originated there or was transplanted from Earth.