McKay presented this lecture, entitled "Drilling in Permafrost on Mars to Search for a Second Genesis of Life," at a NASA Astrobiology Institute Director's Seminar on November 29, 2004.

In this part of his lecture, McKay touches on the fascination with what might be not just another branch on the tree of life, but a new tree. He describes where to look for relic biology in frozen places on Mars.

In its early evolution Mars was wetter, but it was too small to hold onto that water. Now we are looking for life on Mars, hoping to find a second genesis for life.

A second genesis would provide us with a comparative biochemistry. It would also tell us that life in the universe is common. It could also tell us about the early environment on Mars.

These are big questions that are right at the heart of astrobiology.

On Earth, all life is connected in a single tree or web. On Mars, we may be looking for something that's not on that tree. Why do we need another example of life? If we had only apples and no oranges, then we might not understand fruit. So we want to find fruit that's similar but not identical.

We used to think that if we found life on Mars, it would have to be different. But now we know that there is interplanetary transport. We know, for instance, that the Allen Hills meteor came from Mars.

One activity of life is radiation repair. Bugs in the martian permafrost may not have the ability to repair the higher radiation on Mars. So, "it's dead, Jim." But that's okay, because corpses have proteins we may be able to grind up and detect. They may also be capable of reviving.

Where might we find Martian life? Maybe in the soil, in subsurface aquifers. It could be in salt, or in amber. I want to look for preserved life in permafrost.

We find viable bacteria preserved in Siberian permafrost that is 3.5 million years old. At first we thought the Siberian bacteria was dormant. We were both right and wrong.

For about two years, we've looked at the radioactive uptake of carbon into the lipids of the Siberian organisms. Their growth phase is limited by temperature. When they grow at zero degrees, they go through rapid phases in only a few days. At minus 20 degrees, the organisms take hundreds of days to double their uptake.

At higher temperatures their growth slows down - we think because they run out of food. At higher temperatures, the nutrient pool of liquid water is bigger, but molecular diffusion doesn't give them nutrients as fast.

At minus ten degrees, the organisms are inactive as expected, but they are starving because they cannot expand their nutrient pool in the frozen water matrix.

The average temperature on Mars today is a lot lower than minus ten degrees. But we don't know if Mars was warmer or colder in the past.

If you want to find ancient places on Mars, you look for craters, and they are in the south. If you want old, ice-rich ground, you go even further south.

An unexpected discovery of the Mars Global Surveyor was that, in certain places, the crustal magnetic fields are almost as strong as Earth's.

The temperature and pressure has not be raised enough to erase the magnetic fields there, although where there are large craters, these fields may be erased. But the magnetic field tells us these regions are well preserved, and they may be the oldest phenomena we see on Mars.

We may have to drill for old, frozen ice up to 100 meters, maybe 1,000 meters, deep below the surface, where we might find the frozen remains of ancient organisms.

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