Robert D. Maurer Lecture 1997
The 1997 Maurer Lecture was delivered by Professor Richard N. Zare, Marguerite Blake Wilbur Professor of Chemistry at Stanford University, on April 24 in Giffels Auditorium to a standing-room-only crowd. In his public talk entitled Life on Mars?, Professor Zare discussed the evidence that a team of scientists at Stanford University and at the NASA John Space Center led by Professor David McKay has uncovered that strongly suggests primitive life may have existed on Mars more than 3.6 billion years ago. Zare began his talk by noting that our conception of life is strongly influenced by what we find on Earth. We know that life needs water. Mars does not have water now but photographs of Martian surface showing effluvial action, polar ice caps and volcanoes clearly point to a once warm and wet planet. We also know that Mars does not have an atmosphere because its gravity is too weak to hold gaseous atoms too long. He said that we have learned a great deal more about Mars from optical astronomy and from the two Viking Lander Missions of 1976. For example, we know such isotopic abundances as the hydrogen to deuterium ratio, and that it is different from that found on Earth. The Viking Lander Missions also tested Martian surface soil for signs of life. No organics were found. This put a damper on the search for life on Mars. In 1984 scientists found a meteorite in Antarctica. This meteorite, labeled ALH840001, is about the size of a loaf of bread. Its isotopic composition, determined by laser mass spectrometry, clearly point to a Martian origin of this meteorite. A radioactivity analysis shows that the meteorite is more than 3.6 billion years old. Examination of this meteorite under an electron microscope reveals an unusual pattern of organic molecules and several mineral samples that are known products of primitive microscopic organisms on earth such as nanobacteria. Zare said that nanobacteria are the simplest kind of life. He said that the concentration of these substances was sparse on the meteorite surface but much higher in the interior suggesting that the compounds were not the result of terrestrial contamination. He said that only a few years ago no one would have imagined this kind of life possible but recent discoveries in paleo-biology of Earth bacteria that feed on sulfur rather than on sunlight and chlorophyll have changed our conception of life. Professor Zare said that the evidence for life was not based on any one finding but on a combination of things. These include the discovery of the first organic molecule (carbonates) of Martian origin, mineral features characteristic of biological activity and possible microscopic fossils of primitive bacteria-like organisms inside the same meteorite. All of these findings strongly suggest primitive life on Mars more than 3.6 billion years ago. He said that the negative finding of the Viking Mission did not rule out existence of life on Mars because even on earth every rock would not exhibit life forms. He added that his speculation was that there was lots of life on Mars because if life was really rare on Mars the probability that a piece of Mars containing life would hit earth would be indeed small. Professor Zare emphasized, however, that he maintained a certain air of skepticism. He said that these conclusions are the most reasonable and simplest explanation of the evidence, but not proof. Research is a process and not an end result. A consensus that life does exist on Mars would require more experiments and solid findings such as colonies of organisms, or signs of cell division showing the life cycle of such organisms. It is good to question, that is what the scientific method is all about. Professor Zare is renowned for his research in laser chemistry. By experimental and theoretical studies he has made seminal contributions to our understanding of molecular collision processes and contributed significantly to solving a variety of problems in chemical analysis. He is a graduate of Harvard University, where he received his BA in physics and chemistry, and his Ph.D. in chemical physics in 1964. After holding faculty positions at MIT and the University of Colorado, he joined Columbia University in 1969 where he became Higgins Professor of Natural Science. In 1977 he moved to Stanford. Professor Zare is a member of the National Academy of Sciences. He has received numerous national and international awards and honors. These include the National Medal of Science and the National Academy of Sciences Award in Chemical Sciences, the Earle K. Plyler and the Langmuir Prizes of the American Physical Society and the Peter Debye Award of the American Chemical Society. Surendra Singh
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