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Meteorite fragment ALH 84001
Meteorite type: Achondrite
Class: Martian meteorite
Group: ALH 84001
Shock stage: B
Weathering grade: A/B
Country: Antarctica
Region: Allan Hills, Far Western Icefield
Coordinates: 76°55′13″S 156°46′25″E / 76.92028°S 156.77361°E /
-76.92028; 156.77361Coordinates: 76°55′13″S 156°46′25″E / 76.92028°S
156.77361°E / -76.92028; 156.77361[1]
Observed fall: No
Found date: 1984
Total Known Weight (TKW): 1930.9 g
Allan Hills 84001 (commonly abbreviated ALH 84001[1]) is a meteorite
found in Allan Hills, Antarctica on December 27, 1984 by a team of US
meteorite hunters from the ANSMET project. Like other members of the
group of SNCs (shergottite, nakhlite, chassignite), ALH 84001 is
thought to be from Mars. On discovery, its mass was 1.93 kg. It made
its way into headlines worldwide in 1996 when scientists announced
that it might contain evidence for microscopic fossils of Martian
bacteria.
Contents [hide]
1 History
2 Possible lifeforms
3 Origin on Mars
4 Student participation
5 See also
6 References
7 External links
[edit] History
This rock is theorized to be one of the oldest pieces of the solar
system, proposed to have crystallized from molten rock 4.5 billion
years ago. Based on hypotheses surrounding attempts to identify where
extraterrestrial rocks come from, it is supposed to have originated on
Mars and is related to other martian meteorites. The theory holds that
it was shocked and broken by one or more meteorite impacts on the
surface of Mars some 3.9 to 4.0 billion years ago, but remained on the
planet. It was later blasted off from the surface in a separate impact
about 15 million years ago and impacted Earth roughly 13,000 years
ago. These dates were established by a variety of radiometric dating
techniques, including samarium-neodymium (Sm-Nd), rubidium-strontium
(Rb-Sr), potassium-argon (K-Ar), and carbon-14.[2][3]
[edit] Possible lifeforms
On August 6, 1996[4] ALH 84001 became newsworthy when it was announced
that the meteorite may contain evidence for traces of life from Mars,
as published in an article in Science by David McKay of NASA.[5]
The electron microscope revealed chain structures in meteorite
fragment ALH84001Under the scanning electron microscope structures
were revealed that may be the remains—in the form of fossils—of
bacteria-like lifeforms. The structures found on ALH 84001 are 20-100
nanometres in diameter, similar in size to the theoretical
nanobacteria, but smaller than any known cellular life at the time of
their discovery. If the structures are really fossilized lifeforms,
they would be the first solid evidence of the existence of
extraterrestrial life, aside from the chance of their origin being
terrestrial contamination.[6]
The announcement of possible extraterrestrial life caused considerable
controversy at the time and opened up interest in Martian exploration.
When the discovery was announced, many immediately conjectured that
the fossils were the first true evidence of extraterrestrial life—
making headlines around the world, and even prompting U.S. President
Bill Clinton to make a formal televised announcement to mark the event.
[7]
Several tests for organic material have been performed on the
meteorite and amino acids and polycyclic aromatic hydrocarbons (PAH)
have been found. The debate if the organic molecules were created by
nonbiological processes or are due to contamination from the contact
with Antarctic ice is still ongoing.[8][9]
As of 2006, some experts still argue that the microfossils are not
indicative of life, but instead are caused by contamination by earthly
biofilms. It has not yet conclusively been shown how the features were
formed, but similar features have been recreated in labs without
biological inputs.[4] Nevertheless, evidence continues to grow that
nanobacteria do exist, in spite of initial skepticism[10] (based on
the idea that the particles were too small to contain RNA).
Recent studies on ALH 84001 have shown that, although chances are low,
eventually, Martian rocks such as ALH 84001 could actually transfer
Martian life to Earth.[11] Bacterial spores, and rock dwelling
organisms are speculated to survive in space for 5 years, meaning
transfer of Martian life to our planet is theoretically possible.
This article may contain original research or unverified claims.
Please improve the article by adding references. See the talk page for
details. (May 2009)
If Mars's atmosphere at the time life started on Earth was like it is
now, though, survival and propagation of any life form after arriving
would be even less likely. The life form's native environment probably
would be completely unlike anywhere it would land on Earth. Mars has
an atmosphere many times thinner than that on top of Mount Everest,
with almost no water. A life form evolved to survive in such
conditions would almost invariably find dense air to be toxic, as it
would the relatively high temperatures[citation needed]: even the
Antarctic does not get as cold as much of Mars does most of the year.
[12] However, it is hypothesized that ALH 84001 originated from a time
period during which water may have existed on Mars.[4] Other
meteorites that have potential biological markings have generated less
interest because they do not originate from a "wet" Mars. ALH 84001 is
the only meteorite collected from such a time period.[4]
[edit] Origin on Mars
In September 2005, Vicky Hamilton of the University of Hawaii at Manoa
presented an analysis of the origin of ALH 84001 using data from the
Mars Global Surveyor and Mars Odyssey spacecraft orbiting Mars.
According to the analysis, Eos Chasma in the Valles Marineris canyon
appears to be the source of the meteorite.[13] The analysis was not
conclusive, in part because it was limited to parts of Mars not
obscured by dust.
[edit] Student participation
The analysis of ALH84001 was unusual in that an undergraduate student,
Anne Taunton of the University of Arkansas, performed much of the SEM
work used to correlate the suspected nanobacterial fossils with known
terrestrial nanobacterial fossils. NASA's David McKay hired Anne
Taunton for a 10-week student internship to perform the SEM analysis,
but did not inform her about the nature of what she was investigating.
[14] This technique is known as a single blind. Taunton reported the
morphology of nanofossils in ALH84001 to be very similar to
terrestrial samples without knowing that she was describing a Martian
meteorite.
[edit] See also
Panspermia, or more correctly Exogenesis
Deception Point - Fiction around an ALH84001 theme
[edit] References
^ a b "Meteoritical Bulletin Database: Allan Hills 84001".
http://tin.er.usgs.gov/meteor/metbull.php?sea=alh+84001&sfor=names&ants=&falls=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&phot=&snew=0&pnt=no&code=604.
^ Nyquist, L. E.; Wiesmann, H.; Shih, C.-Y.; Dasch, J. (1999). "Lunar
Meteorites and the Lunar Crustal SR and Nd Isotopic Compositions".
Lunar and Planetary Science 27: 971. Bibcode: 1996LPI....27..971N.
^ Borg, Lars; et al. (1999). "The Age of the Carbonates in Martian
Meteorite ALH84001". Science 286 (5437): 90–94. doi:10.1126/science.
286.5437.90.
^ a b c d Crenson, Matt (2006-08-06). "After 10 years, few believe
life on Mars". Associated Press (on space.com.
http://www.space.com/scienceastronomy/ap_060806_mars_rock.html.
Retrieved on 2006-08-06.
^ McKay, David S.; et al. (1996). "Search for Past Life on Mars:
Possible Relic Biogenic Activity in Martian Meteorite ALH84001".
Science 273 (5277): 924–930. doi:10.1126/science.273.5277.924.
^ McSween, H. Y. (1997). "Evidence for life in a martian meteorite?".
GSA Today 7 (7): 1–7. PMID 11541665.
^ Clinton, Bill (1996-08-07). "President Clinton Statement Regarding
Mars Meteorite Discovery". NASA. http://www2.jpl.nasa.gov/snc/clinton.html.
Retrieved on 2006-08-07.
^ Bada, J. L.; Glavin, D. P.; McDonald, G. D.; Becker, L. (1998). "A
Search for Endogenous Amino Acids in Martian Meteorite ALH84001".
Science 279 (5349): 362–365. doi:10.1126/science.279.5349.362.
^ Becker L., Glavin D. P., Bada J. L. (1997). "Polycyclic aromatic
hydrocarbons (PAHs) in Antarctic Martian meteorites, carbonaceous
chondrites, and polar ice". Geochimica et Cosmochimica Acta 61: 475–
481. doi:10.1016/S0016-7037(96)00400-0.
^ Cisar J, Xu D, Thompson J, Swaim W, Hu L, Kopecko D (2000). "An
alternative interpretation of nanobacteria-induced biomineralization".
PNAS 97 (21): 11511–11515. doi:10.1073/pnas.97.21.11511. PMID
11027350.
^ Paine, Michael (October 1996). "Transpermia - microbes hitch a ride
between planets". http://users.tpg.com.au/users/tps-seti/swaprock.html.
Retrieved on 2008-03-21.
^ :: NASA Quest > Aerospace ::
^ Birthplace of famous Mars meteorite pinpointed. New Scientist
article. URL accessed March 18, 2006.
^ Taylor, Michael Ray, 1999. Dark Life. 0684841916, p. 90.
Mittlefehldt D. W. (1994) "ALH84001, a cumulate orthopyroxenite member
of the SNC meteorite group". Meteoritics, 29, 214-221. URL accessed
March 18, 2006.
Stephan T., Jessberger E. K., Heiss C. H. and Rost D. (2003) "TOF-SIMS
analysis of polycyclic aromatic hydrocarbons in Allan Hills 84001".
Meteorit. Planet. Sci. 38, 109–116.
[edit] External links
NASA - The ALH 84001 Meteorite
Allan Treiman's dissection of ALH84001 literature for the non-
specialist
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