Extreme Environments

At one time I had a research project being conducted in my lab which involved organisms which were able to grow at low temperatures. This was some 3 decades ago and there was a prevailing interest in such organisms since we had space probes to Mars, for example, which were attempting to discover if life existed elsewhere in our universe. Since that time, we have found numerous examples of life in such places as oil reservoirs, solid rock, acidic waste from mining operations, and many other places once considered too inhospitable for life. There have been bacteria found at the bottom of an Alaska pond which were frozen 30,000 years ago. When thawed, they proliferate nicely.
This has been known to microbiologists for years, but I recently read about the discovery of organisms being discovered in rocks 2 miles below the earth's surface which are able to live and reproduce using the radioactivity in uranium, and other substances to exist. Basically, the radioactivity breaks down water and sulfur to produce sulfate which the bacteria use to grow, metabolize, and reproduce. The significance of this is that these orgainsms are able to exist and reproduce in the complete absence of sunlight, which has been previously assumed to be required for all life on earth. Since this is no longer the case, life on Mars and other planets is not now considered such a remote possibility and we should perhaps go back and look at the earlier conclusion that no life can be found on Mars.