Evidence of past life on Mars in alh84001
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- ALH84001 – The Discovery.
- Figure 1 - ALH84001 (WIKI1).
- Arguments For “Life” in ALH84001
| Evidence of past life on Mars in ALH84001
Brad E. Rhodes, HET618, Swinburne Astronomy Online Introduction Finding life on some distant world is dream of every astrobiologist. It just has to be life. It does not have to be complex. Simple microbes would suffice to prove that life exists somewhere other than Earth. Human beings might then have high hopes of finding their distant complex cousins some day. What scientists did not expect was to find possible evidence of extraterrestrial life on Earth. Approximately 13,000 years ago, a meteorite from Mars crash landed in Antarctica (LPI1). Given the simple name of ALH84001 for where it was found, this meteorite would turn the astrobiology world upside down in 1996. Scientists announced they had observed what appeared to be fossilized bacteria in ALH84001 (LPI2). This paper will briefly review the origins of ALH84001, the arguments for and against the possibility the meteorite contains fossilized Martian bacteria, and the steps the astrobiology community would expect to take to confirm or deny this discovery. ALH84001 may be the first evidence that life exists beyond the boundaries of Earth’s biosphere, but then again it may not. ALH84001 – The Discovery. I 
Figure 1 - ALH84001 (WIKI1). n 1984, an unassuming meteorite was discovered in Alan Hills, Antarctica (LP1, WIKI1). Named ALH84001 for the location of discovery, the year of 1984, and 001 for the first object found, it was believed to be a Mars meteorite (WIKI1). The designation Mars meteorite comes from scientific analysis conducted indicating they “possess chemical, isotopic, and petrologic features consistent with data available from Mars” (WIKI2). Such data was available from the National Aeronautics and Space Administration (NASA) Viking Landers soil analysis experiments conducted in the mid-1970s (NASA1). To date, 34 Mars meteorites have been discovered on Earth. They are known as the SNC group of made up of “achondritic (stony) meteorites (by number): shergottites (25), nakhlites (7), and chassignites (2)” (WIKI2). ALH84001 is a shergottite (WIKI2). Its approximate age is 4.5 billion years, much older than other shergottite which only date to around 1.3 billion years (WIKI2). ALH84001 is an igneous rock, meaning that appears to have formed from the lava of an ancient Martian volcano (LPI1). Figure 1 shows the exterior of ALH84001 (WIKI1). There may be some doubt as to whether ALH84001 is really from Mars. The right circumstances could knock a rock off of Mars and set it on a collision course with Earth. In the case of ALH84001, an asteroid with a diameter of 0.5 to 2.0 kilometers likely struck Mars (LPI1). This would have accelerated what would eventually become ALH84001 faster than Mars’ escape velocity of 5 kilometers per second, slinging the object into orbit around the Sun (LPI1). The influence of Jupiter and further interactions with other bodies set ALH84001 on track for its eventual landing in Antarctica (LPI1). Analysis of cosmic ray exposures shows that ALH84001 traveled in space for nearly 16 million years before coming to rest on Earth (LPI1). Trace amounts of gases analyzed from ALH84001 show consistency with the Martian atmosphere as sampled by the Viking landers (LPI1, NASA1). After its discovery in 1984, ALH84001 lived a quiet life. That was until 1996 when a stunning announcement was made by NASA scientists (LPI2). Arguments For “Life” in ALH84001 The detailed analysis of ALH84001 lead by David McKay had a simple goal: “look for signs of past (fossil) life within the pore space or secondary minerals of this Martian meteorite” (SCI1). McKay’s team had a difficult task for two reasons. First, they only had a small piece of Martian crust to examine. Second, the team only had Earth-type “biomarkers” to use as reference. If the biomarker did not resemble something recognizable with similarities to known Earth fossils, something might be missed. Initial investigations were made along original fractures on the meteorite. The team found carbonate globules which under mass spectrometer microprobe showed the presence of polycyclic aromatic hydrocarbon (PAH) molecules (SCI1). T 
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