The Search for Life on Mars

This book is a little like "Here be Dragons," (Koerner, LeVay, Oxford University Press, 2000) and "Rare Earth," (Ward, Brownlee, Copernicus, 2000) except that it is more focused and specific than the others. While Koerner, LeVay, Ward, and Brownlee consider the possibility that life exists outside the solar system, Walter limits the scope of his book to the question of whether microbes exist, or once existed, on Mars. Life outside of earth has never been unambiguously observed and verified. Consequently, discussions about the possibility of life beyond earth inevitably begin with thoughts about how life originated here. There seems to be an emerging sense that life is the result of a universe that is naturally self-organizing (Stuart Kauffman is in this camp. See his book "At Home in the Universe, Oxford University Press, 1995). According to this point of view, life is all but certain to arise on any planet having the basic chemicals and physical conditions found on earth 4 billion years ago. Given this hypothesis - that life arises quickly and naturally in the proper environment - it's natural to ask if any other planets in the solar system have (or had) the necessary ingredients. If they did, we should look to see if life evolved there. Since there is growing evidence that Mars had a distant past with some of these conditions, it seems more and more important that we look for life on Mars. Finding evidence of life there would buttress the concept that life readily evolves given the proper environment. Obviously, if that's the case, it holds enormous consequences for modern science.Walter has a nice chapter on the tree of life, and describes recent information showing that "all the lowest branches of the tree are occupied by hyperthermophiles." The discovery that life exists on earth under extreme conditions (like those of deep-sea thermal vents) has increased the hope among scientists that it might also have evolved and flourished on Mars many thousands of millions of years ago. He also shows how genetic transfer between species happens today, and was probably common among our earliest ancestors, so that the whole concept of a "tree of life" becomes somewhat tangled during the earliest stages of the evolution of life. Instead of a tree, the topology looks more like a web, with the roots of the tree (consisting of Bacteria, Eucarya, and Archaea) rising out of this web. The expectation of finding evidence of life on Mars depends on the type of environment that Mars supported in the distant past, and the circumstances under which life arose on earth. It also depends on how easy it is to ascertain the evidence of fossilized ancient microbial life. It turns out that identifying evidence of microbes in very old rocks is a pretty hard thing to do. To illustrate this, Walter describes the difficulty of identifying stromatolites in ancient rocks. This was new information for me, and a real insight into the nuts and bolts of making

Malcolm Walter has written a fascinating guide to where we should look for current or past life on Mars. As a non-scientist I was not quite sure what to expect in buying this book, but what I found was a thoughtful discussion of how one scientist would explore the red planet for signs of life. Walter gives a short, understandable review of the scientific discoveries to date from the past NASA missions as a prelude to what to expect in the future. However, his background is in palaeobiology on Earth, which I learned is the study of fossilied life. Having absolutely no knowledge of this field myself, I sometimes felt a little lost in his technical discussions and wasn't always sure that I wanted to know as much as he told me about microbe fossils on Earth. Nevertheless, the thrust of his arguments and points he made were all clear. The heart of his case is that there is a lot we can learn from palaeobiology on Earth that should inform how we search for life, which may very well only be fossilized former life, on Mars. The importance future extensive scientific exploration for signs of past or present life on Mars is also well made. Overall, this short book (170 pages including the index) is worth the the time, and for a layman the effort, for anyone who has even a passing interest in this subject.