"Note to ER: When I posted the words: "Is it unreasonable to assume that the laws of physics may have allowed life on Mars." I was thinking that pretty well all of the minerals that exist on Earth have also been detected on Mars, the only difference is in the quantities compared to each other, for instance the atmosphere on Mars has more carbon dioxide and less oxygen than the atmosphere on Earth. There are other differences that are known to anyone that is even mildly interested in knowing something about Mars. Such as; Mars is smaller, it is further from the sun, it has less atmosphere, it has less water, etc., but what was going through my mind was: Do these variations definitively exclude the existence of life on the planet."

"In 3.5 million-year-old crust almost 1,000 feet beneath the bottom of the ocean, researchers found moderately hot water moving through the heavily-fractured basalt. The water was depleted in sulfate and greatly enriched with ammonium, suggesting biological activity in a high-pressure, undersea location far from the types of carbon or energy sources upon which most life on Earth is based.
....
According to Steve Giovannoni, an OSU professor of microbiology and one of the co-authors of the publication, the work represented a highly complicated "plumbing job," among other things. It took advantage of an existing hole and pipe casing that had been drilled previously in that area by the Ocean Drilling Program, through about 825 feet of sedimentary deposits on the ocean floor and another 175 feet of basalt, or hardened lava about 3.5 million years old.

Using the existing casing, scientists were able to fit an experimental seal and deliver to the seafloor, for testing and characterization, the crustal fluids from far below.
...
As more research such as this is done, we'll probably continue to be surprised at just how far down we can find life within the Earth, and the many different environments under which it's able to exist," Rappe said.

The deep ocean crust, the researchers said, is an immense biosphere in its own right that covers most of the Earth."
http://www.sciencedaily.com/releases/2003/01/030102224030.htm