From benr@umd.edu Fri Oct 29 18:15:13 2004 Date: Wed, 27 Oct 2004 14:44:29 -0400 From: Ben Roberts To: Doug Hamilton Subject: My article abstract Article: Carlton C. Allen, Luke W. Probst, Beverly E. Flood, Teresa G. Longazo, Rachel T. Schelble and Frances Westall, Meridiani Planum hematite deposit and the search for evidence of life on Mars--iron mineralization of microorganisms in rock varnish, Icarus, Volume 171, Issue 1, September 2004, Pages 20-30. This article discusses the feasibility of recovering evidence of past life from Meridiani Planum on Mars by investigating an analogous possibility of finding similar evidence of life in rock varnishes in Earth's deserts. Any discovery of past life on Mars would have profound implications for how Mars' climate has changed over time. Meridiani Planum is covered by a layer of hematite, which is a mineral oxide of iron. There are five methods identified (by other researchers) for forming this hematite--and four of them involve liquid water, which by itself is a compelling reason to search for life in this area. However, each of these four formation scenarios has different implications for how evidence of life would be embedded in the hematite, and it is also possible that some methods of the hematite formation would preclude recovering any evidence of past life. The paper summarizes previous research done which demonstrates the ability to recover evidence of life for three of the four water-related methods of hematite formation. The authors designed experiments to be able to recover indications of life for hematite formation by the fourth method, looking in a thin layer of rock varnish for evidence of life on Earth. The methods the authors used were the collection of varnish from two sites, one in Arizona and one in Australia. Electron microscopes were the primary tool used to look for any evidence of life. They discovered that microcolonial fungi evidence was much more common than fungi and bacteria compared to the expected populations. The detection of bacteria seemed to rely upon detection of carbon and other elements not normally found in the rock, but most of the carbon from the life that was there had been removed over time. Because of this very few examples of bacteria were located, although the authors did make two successful identifications of bacteria as cast in minerals. The microcolonial fungi were detected because they had been coated in minerals, preserving their shape. The researchers also found from dating their samples that none of the life forms discovered were very old, which may remove hope of finding evidence of life on Mars with this technique. The paper concludes by applying the research to the Mars rover Opportunity, which was exploring Meridiani Planum. The authors concluded that Opportunity or any other probe sent to the area would have poor chance of detecting evidence for life because it involved the use of microscopy. The authors suggest the eventual use of a sample return mission so that the hematite may be analyzed.