Evidence of past life on Mars in alh84001
Figure 2 - Comparison of ALH84001/Columbia River Basalt
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- Figure 3 - Possible Water Deposit on Mars (NASA3)
- Arguments Against “Life” in ALH84001
- Figure 4 - ALH84001 cracks that display a plagioclase, silica, and other carbonates (PRSD3).
- Next Steps – finding “Life” on Mars
Figure 2 - Comparison of ALH84001/Columbia River Basalt (http://www.astrobiology.com/adastra/its.dead.jim.html). he presence of PAHs is what interested the scientists. According to the team’s publication in the August 1996 (Journal) Science: “On Earth, PAHs are abundant as fossil molecules in ancient sedimentary rocks, coal, and petroleum, where they are derived from chemical aromatization of biological precursors such as marine plankton and early plant life.” With a little luck, McKay had found what they were looking for: a recognizable biomarker. The carbonates found in ALH84001 seem to indicate that the Martian surface supported liquid water several billion years ago. Further microscopic investigation of ALH84001 revealed the presence of “ovoid” shapes that seemed to look like fossilized bacteria (SCI1, LPI2). Figure 2 shows a comparison of ALH84001 shapes and similar Earth-based fossils from the Columbia River, Oregon. PAHs have been shown to form during the decomposition of certain bacteria. Unfortunately, PAHs also occur from certain everyday human activities. To demonstrate that the PAHs found on ALH84001 had not occurred in the laboratory, the team did much to show that the molecules were legitimate. Also, the PAHs on ALH84001 were found in the inner part of the meteorite. Additionally, the team reviewed ice cores to show the difference between ALH84001 PAH levels and the Antarctic surface. The “contamination check” showed that the PAHs in ALH84001 did not come from the Earth’s surface. This evidence seems to support McKay’s theory that the PAHs were formed as the result of a biological process (SC1, LPI2). F 
Figure 3 - Possible Water Deposit on Mars (NASA3) rom a strict scientific perspective, McKay and his team have done everything right. They isolated their samples using strict laboratory protocols. They showed that ALH84001 PAHs were not the result of Earth-based contamination. Finally, they have what appears to be fossilized evidence within the meteorite that can be directly correlated to Earth-type bacteria. Unfortunately, there was not direct proof that water ever existed on the surface of Mars. The data analysis from the Viking Landers indicated that Mars was a dry and desolate place. That was until 2004 and the Opportunity Rover. Operating on the Meridiani Planum, Opportunity discovered strong evidence that water once flowed on the surface of Mars. Using Opportunity’s x-ray spectrometer, NASA Jet Propulsion Laboratory (JPL) scientists examined sulfur formations that would have only formed in the presence of briny water (NASA2). Additionally, comparison photographs (figure 3) by the Mars Global Surveyor’s (MGS) Mars Orbiter Camera taken in 1999 and in 2005 seem to indicate that water still flows on the Martian surface occasionally (NASA3). These revelations add credence to the possibility that formations in ALH84001 may actually be the first evidence of life beyond Earth. Even with credible scientific evidence from ALH84001 and recent indications that Mars’ past and present may be watery, doubts still exist. Arguments Against “Life” in ALH84001 There are a variety of arguments against fossilized life in ALH84001. The most obvious is that in 1996, the best surface data from Mars came from the Viking landers. That data showed absolutely nothing. While the experiments have been criticized, Viking did not even find anything reactive in the soil that might indicate the possibility of life (NASA1). Using this as a basis, Mars appears to be a barren world. Therefore, the announcement of fossilized life in ALH84001 would seem to contradict all of the previous evidence. It is important to note that the latest observations gathered by the Opportunity rover and MGS seem to show water may be a more recent phenomenon on Mars (NASA2, NASA3). However, this data does not show presence of life, nor does it indicate conditions were ever able to support it. Having environmental conditions on the Martian surface able to support life is critical to whether or not bacteria may have fossilized in ALH84001. The first environmental consideration is overall planetary temperature. The time at which ALH84001 formed (4.5 billion years ago), the Sun’s luminosity was thirty percent less than it is today (NASA4). This means that Mars’ surface temperature was even less than it is presently (20 degrees Celsius versus minus 60 degrees Celsius) (UNI1, PRSD1). While life has been found in extreme environments on Earth much had its beginnings in a consistently warm watery environment (UNI1). Mars was definitely not warm. There are additional factors to consider as to whether Mars supported life in the past. Probably the most interesting is Mars’ present lack of a magnetic field. As seen on Earth, a magnetic field is critical to protecting its fragile atmosphere (UNI1). Magnetometer readings from MGS show that Mars once had a magnetic field (eerily similar to the “striping” seen in Earth’s oceans) (NASA5). Yet for some reason, the mechanism that produced Mars’ magnetic field stopped. The result was the planet’s tenuous atmosphere was slowly stripped away. The Martian atmosphere was perhaps thick enough to support the processes for life, but did it exist long enough to support fossilization in ALH84001? B 
Figure 4 - ALH84001 cracks that display a plagioclase, silica, and other carbonates (PRSD3). eyond just the lack of evidence supporting the formation of life at the time ALH84001 was formed, there is much controversy surrounding the carbonates in the rock. In 2002, at the University of Hawaii’s Planetary Science Research Discoveries (PSRD), a team found additional carbonates besides PAHs (PRSD2). The mineral they found was called periclase (made of magnesium oxide (MgO)). Periclase and other carbonates tend to form in voids of magnesium rich rocks (as shown in figure 4). Additionally, the crystalline structures in the carbonates seem to be of natural formation instead of biological. The team also surmised that the “shock-heating” experienced by ALH84001 would have significantly changed the properties of biologically formed carbonates. It is also possible that carbonates formed as a result of shock heating (PRSD2, PRSD3). All of this adds to the many questions about ALH84001. According to Andrew Knoll’s “A Martian Chronicle” in The Sciences, the evidence found in ALH84001 appears circumstantial. This does not make for good science. Clearly, the doubt regarding the “fossils” in ALH84001 means astrobiologists must continue to look! If only the fossil had been something recognizable such as plant leaf. Next Steps – finding “Life” on Mars ALH84001 captured the interest of the scientific community. If the findings are correct, this is the first evidence that life has existed beyond Earth. If the findings are not correct, ALH84001 is just another meteorite from Mars. There are at least four options: 1) Complete a Mars Sample Return Mission as proposed by NASA and European Space Agency (ESA). The challenge for such a mission is picking the most likely place where life might have formed/fossilized. These missions are not expected to begin until the middle of the next decade (NASA6, ESA1). 2) Accomplish human exploration of Mars and sample return. This the goal of NASA Constellation program spearheaded by the Ares V rocket. A manned Mars mission would face the same challenge as option one. Unfortunately seeing a human being on Mars will not occur until after 2020 (NASA6). 3) Another possibility suggested by Andrew Knoll is to look for subterranean water on Mars. If life still exists, perhaps it still finds safe harbor there (Knoll). Finding underground water on Mars implies that options one or two have been successful. 4) Finally, an easy solution to confirm ALH84001 would be to study existing samples for similar fossils.
“ALH84001”, Wikipedia, 31 March 2007, http://en.wikipedia.org/wiki/ALH84001 (WIKI1) “Aurora Exploration Programme: Mars Sample Return”, 04 August 2005, ESA, http://www.esa.int/SPECIALS/Aurora/SEM1PM808BE_0.html (ESA1) Boen, Brooke, “ARES V Cargo Launch Vehicle”, 23 March 2007, NASA, http://www.nasa.gov/mission_pages/constellation/ares/aresV.html (NASA7) Hardin, Mary, “Magnetic Strips Preserve Record of Ancient Mars”, NASA JPL, 29 April 1999, http://www.jpl.nasa.gov/releases/99/mgsmag.html (NASA5) Kaufmann, William J. and Freedman, Roger A., Universe (Fifth Edition), © 1999, W.H. Freeman and Company, New York (UNI1) Knoll, Andrew H., “A Martian Chronicle”, The Sciences (magazine), July/August 1998, pages 20-26 “Mars meteorite”, Wikipedia, 26 February 2007, http://en.wikipedia.org/wiki/Martian_meteorite (WIKI2) McKay David S., et al., “Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001”, Science (Journal), Volume 273, 16 August 1996, page 273 (SCI1) “Missions to Mars”, 01 April 2007, NASA, http://mars.jpl.nasa.gov/missions/future/futureMissions.html (NASA6) “NASA Facts: Viking Mission to Mars”, NASA JPL, 1988, http://www.jpl.nasa.gov/news/fact_sheets/viking.pdf (NASA1) Scott, Edward R.D. and Barber, David J., “Resolution of a Big Argument About Tiny Magnetic Minerals in Martian Meteorite”, Planetary Science Research Discoveries, 13 May 2002, http://www.psrd.hawaii.edu/May02/ALH84001magnetite.html (PRSD2) Scott, Edward R.D., “Shocked Carbonates May Spell No Life in Martian Meteorite ALH84001”, Planetary Science Research Discoveries, 22 May 1997, http://www.psrd.hawaii.edu/May97/ShockedCarb.html (PRSD3) Taylor, G. Jeffrey, “Martian Meteorites Record Surface Temperatures on Mars”, Planetary Science Research Discoveries, 29 July 2005, http://www.psrd.hawaii.edu/July05/Mars_paleotemp.html (PRSD1) Treiman, Allen H., “Fossil Life in ALH 84001?”, Lunar and Planetary Institute, http://www.lpi.usra.edu/lpi/meteorites/life.html (LPI2) Webster, Guy, “Opportunity Rover Finds Strong Evidence Meridiani Planum Was Wet”, 02 March 2004, http://marsrovers.nasa.gov/newsroom/pressreleases/20040302a.html (NASA2) Webster, Guy, “NASA Images Suggest Water Still Flows in Brief Spurts on Mars”, 06 December 2006, http://www.nasa.gov/mission_pages/mars/news/mgs-20061206.html (NASA3) “What is ALH 84001?”, Lunar and Planetary Institute, http://www.lpi.usra.edu/lpi/meteorites/The_Meteorite.html (LPI1) Directory: ~tjb -> swin20071 -> essays essays -> Evidence of Past Life in Mars in alh84001 The Role of Contamination ~tjb -> Physics 107 homework assignment #1 Cutnell & Johnson, 7th ~tjb -> Physics 107 homework assignment #7 Cutnell & Johnson, 7th Download 189.79 Kb. Share with your friends:
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