Where I Am Today

My studies at NASA have lead me in several directions. An important part of my research deals with the origin of stromatolites, which are thin-layered sedimentary structures that are produced by communities of microorganisms. But I have also been interested in how some of the tiny microbes that create stromatolites become fossils. We have actually found tiny microfossils in rocks as far back as 3.5 billion years. Question is, how do these tiny creatures get preserved and why? By understanding such things we can learn more about the ancient environment of the early Earth, and also improve our chances of finding evidence of ancient life in rocks.

I'm still working on these problems. It turns out that on the present Earth, microorganisms tend to thrive in extreme environments; places that are either too hot, too cold, or too salty or acidic for larger complex organisms. I have looked at bacterial life and their fossils in lots of extreme environments. But in trying to better understand how the earliest communities lived, I have mostly focused on life at high temperatures, that is, on microbes that live in hot springs found in places like Yellowstone National Park. I have spent the last five summers in Yellowstone trying to learn more about how the high-temperature communities survive, interact and become fossils. This is important for interpreting the fossil record of early life on Earth. We believe that the last common ancestor of living species on Earth lived at very high temperatures. We know this because when we compare the DNA in all living things, we can make a "tree of life" that shows how things are related. Turns out that the most primitive things, that is, the species that occur near the trunk of the tree, are all high-temperature bacteria, most of which live in hot springs and geysers. So these are good places to go to find conditions similar to what prevailed on the early Earth.

But the story doesn't end there. Because hot springs are such good places to fossilize microorganisms, these environments are also natural places to explore for fossil life on Mars. So, we have also been looking at images of the surface of Mars for the most likely spots for ancient hot-spring deposits. If we can find such deposits, we will want to go there and bring rocks back from those places to look for microfossils. This is in our present plan for Mars exploration, and has been really given a boost by the recent report of possible life in the Martian meteorite, ALH84001, which was found in Antarctica. Although I do not think this rock from Mars has definitive evidence of life, it does have organic chemicals that were preserved much in the same way we see things preserved in hot springs on Earth. NASA's Mars Global Surveyor and Mars Pathfinder and Russia's Mars '96 mission are scheduled for three separate launches in November and December 1996. We hope that with the new information we get back from these missions, we will better know where to go to bring samples back to Earth that may help us answer the question, "Did life ever develop on Mars?"