They were studying underground environments and discovered areas that were inhospitable to life. Inhospitable, that is, until they were colonized by tough microbes. These organisms improved conditions so much that other creatures could move in. This has important implications when looking for life on other planets.

Living in Harmony
The team, led by David Fern�ndez-Remolar of the Centro de Astrobiolog�a in Spain, expected the underground areas to be barren. They were understandably surprised to find places perfect for microscopic life. What was going on? The answer came in the form of tiny microbes that reacted with the rocks and then gave off heat. It wasn't much -- just enough to raise the overall temperature and make the environment more liveable.

So just by colonizing an area under the ground, the microbes made it habitable for other forms of life. They're like construction workers, building comfortable homes for others. Of course, the microbes weren't trying to make conditions better -- it's just a happy side-effect of their natural processes.

The researchers also found that the acidic conditions they were expecting had been neutralized by metals, making the water safe for life. The microbes aren't involved in this process, although they do benefit from it.

Such a two-tiered system could make areas on other planets relatively cosy for simple life. It can even help us find evidence for past or present life on Mars: we could look for slight temperature increases near the surface, or the chemicals that reduce water acidity. Such tell-tale signs would indicate that the same mechanisms working in Rio Tinto could be happening on Mars.

Martian Rock Pools
Using these discoveries, we can imagine how life on Mars could have developed. Conditions on the red planet in the past were very different from today. There was probably warm water underground, which would have helped make certain metallic ores. These are important as they could have been used as food for the "construction worker" microbes.

As they grew and reacted with the rocks around them, the microbes would have generated heat, making their environment warmer. It would have still been bitterly cold, but salts would have kept the water liquid, even if the temperature dipped below the freezing point.

This shallow water could have protected the microbes and any other life from the sun's normally lethal ultraviolet radiation.

Metals in the rocks would have made sure that the water wasn't too acidic. Over time other organisms could have colonized the area after the first microbes had made conditions much nicer for life. The result would have been simple Martian rock pools teeming with strange microbial life.

Looking into one such pool with a microscope would be a dream come true for astrobiologists. "It may be possible that the inner habitats of planets were not only the first refuge of life, but may also have become the last for planets such as Mars," the researchers report.

Once our technology for studying planets around other stars improves, we could search for signs of life like this around distant worlds. They may not be as glamorous as aliens we could talk to, but these hard-working microbes may well provide the foundations for areas filled with exotic life.

The research is detailed in the Spring 2008 issue of the journal Astrobiology.

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