The ALH 84001 Controversy - by Ricky Leon Murphy:
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The ALH 84001
The rock is called ALH 84001 and on August 7, 1996 an
announcement was made that indicates ancient, microscopic life existed on Mars.
By studying a rather un-assuming potato shaped rock, it was determined not only
that it originated from Mars,
but it also contained complex organic compounds, magnetite, carbonate minerals
and even fossils of rod-like structure. While it seems that scientists were not
looking for anything in particular when studying this rock, they seem to have
stumbled on a proverbial gold mine – or have they? While the evidence to support
the presumption of life seems un-deniable, the question many are asking is have
all other explanations been ruled out. Since then, this small self-effacing rock
has been the hotbed for debate for the past 10 years. The difficulty in choosing
a side is two-fold: not once has either side denied the possibility of life on
Mars, and there are limited samples to provide evidence to support any claims of
life. But ultimately it seems the evidence strongly suggests that life did exist
A Brief History:
With data from the Mars Global Surveyor and the Mars
Exploration Rovers (Spirit and Opportunity), the case for water once flowing on
Mars is pretty strong. The concentration of CO2 in the atmosphere is thought to
have been enough to sustain liquid water about 3.7 to 3.9 billion years ago. It is also
during this time that heavy bombardment of Solar System debris had ceased [R5].
With the necessary conditions available (a heat source, an atmosphere,
volcanism), it is possible life could have appeared. As the planet cooled
(because is small), volcanism ceased, greenhouse gasses (no longer replenished)
escaped into space and the water, with further impacts, would have evaporated –
lost into space [R5].
Any life that had appeared would now have dried up, locked into the crust. When
a meteor impacted the crust 16 million years ago, it sent pieces of it into
space (because the gravity is not as strong as Earth) - and pieces of the crust
would still have features of water erosion due to lack of tectonics. As the debris traveled
through space for a time, it ultimately landed in Antarctica some 13,000 years
This 1.9 kilogram, potato shaped rock was picked up at Alan Hills, Antarctica on
December 27, 1984 [R2][R4].
It sat on a shelf for about 10 years before being examined, and that is when all
the excitement hit the fan.
A paper was published on August 16, 1996 in Science
magazine by the team studying this meteorite (now called ALH 84001)
led by David S. McKay. This paper outlines four pieces of evidence to support
that life once existed on Mars. These are:
- Carbonate minerals were detected similar to carbonate
deposits of Earth-based biological life
- The presence of Polycyclic
Aromatic Hydrocarbons (PAHs) – complex organic molecules
- The presence of the mineral Magnetite
- The presence of what appears to be rod-like
It seems the evidence is surprisingly overwhelming that
life did exist on Mars, but since this announcement was made alternate
explanations have been offered to explain each of these attestations.
The potato shaped ALH 84001 (Image
By using Stereo Light Microscopy (SLM), High-Resolution
Transmission Electron Microscopy (HRTEM) and Energy Dispersive Spectroscopy
(EDS), McKay’s team concluded that fractures within ALH 84001 contain carbonate
material – specifically Iron, Calcium, Sulfur, Magnesium and Phosphorus [R6].
It is suggested that these deposits were formed when water poured through the
rock. This alone is not indicative of life, but according to the McKay team this
first piece of evidence is the base by which the other three are supported [R2].
The problem with this first piece of evidence is that while
the presence of these minerals does imply that water did flow through, this same
material can also form given the right conditions. For example, this same
material can form without any biologic influence under high temperatures of
several hundred degrees Fahrenheit [R4].
Water is not necessary.
Polycyclic Aromatic Hydrocarbons:
Polycyclic Aromatic Hydrocarbons – or PAHs – are a complex
form of organic material that is believed to form by biological breakdown like
decomposing plant life [R4];
this material is believed to be formed by bacterial decomposition. The organic
material is made up of phenanthrene, pyrene, chrysene, benzopyrene and
In order to rule out any contamination, PAHs levels were compared between ALH
84001 and the area surrounding Alan Hills. It was concluded by McKay’s team that
the PAHs within ALH 84001 were not cross-contaminated with the Alan Hills site.
While McKay’s team confirmed the levels of PAHs between
Alan Hills and ALH 84001 suggest these formed on Mars, there is evidence that
contamination could still be a factor. A second meteorite from Mars, one much
younger than ALH 84001 also contains the same levels of PAHs. This demonstrates
the likely hood of contamination by the Antarctic ice sheets [R4].
In addition, the formation of PAHs is not required to form by biologic activity
and may form by other means [R5].
For example, PAHs can form in interstellar space as well as smokestacks and
automobile engines [R4][R5].
While the presence of Magnetite can be formed by way of
organic or inorganic processes, it has been established by
McKay et al that the Magnetite present in ALH 84001 is similar to Earth
formed Magnetite. It is further established that the Magnetite crystals were
formed by biological processes (bacterial decomposition) based on the
Magnetite’s hexa-octahedral crystal shape – a process that is not found by
formation through inorganic methods [R7].
While the Magnetite evidence seems compelling, another
group examining the Magnetite crystals discovered defects and fracture not
consistent with the organic formation of the crystals – instead indicate
formation by inorganic methods under high temperatures [R4].
In addition, the presence of Magnetite and Greigite (which is still unconfirmed
strongly suggest the appearance of biological formation is simulated by
temperature changes [R5].
Perhaps the most dramatic piece of evidence is the presence
of microfossils of what looks like nano-bacteria. In fact, the microfossils
found look exactly like the nano-bacteria found on Earth (although much smaller)
Further, the age of the rock implies that Mars was wetter and warmer in the past
so that the formation of these nano-bacteria is possible [R2][R6].
It is these micro-fossils that support the evidence for PAHs [R13].
A scanning electron microscope was used to capture the
image of the micro-fossil in question, but it is argued that the process of
scanning can produce “fractures” that can look like these microfossils [R4].
While there is no mention of any possible contamination by terrestrial sources,
it is suggested that these microfossils can be mineral grains and therefore
An example of this would be fossilized mineral grains found in Columbia River
In addition, the nano-bacteria have a size limitation of 150nm for replication [R16]
and the samples in ALH 84001 are smaller.
Aware of the debate with the ALH 84001 results,
Gibson and McKay et al released a paper with additional supporting data. It
is acknowledged that contamination and misinterpretation is possible; however,
data discovered within two additional Mars meteorites – Nakhla and Shegotty – as
well as confirmation from a second examining group support the initial claims.
The team acknowledges the process of carbonate material can
form under high temperature. It is asserted that early Mars was warmer and
wetter providing the right conditions for the carbon material to form. In
addition, impacts on Mars would also provide the right conditions for the
carbonate materials to form as well.
Regarding Polycyclic Aromatic Hydrocarbons:
The McKay team reports that PAHs are not a diagnostic for
life, but PAHs present with carbonate material supports life. Contamination has
been ruled out by other teams examining ALH 84001. In addition, PAHs have also
been detected in the meteorite Nakhla.
Additional teams studying ALH 84001 have also ruled out any
terrestrial contamination as well as any formation by result of high temperature
and shock. Reexamination demonstrates three types of Magnetite crystals are
present suggestion formation through abiotic process in a low temperature
environment – ruling out fracturing caused by high temperatures, or temperature
fluctuations suggested by the presence of Greigite.
Regarding Rod-Like Microfossils:
While it is accepted that the micro-fossils can be
fossilized minerals, nano-bacteria can also mineralize. Terrestrial analogs have
been detected in the blood-stream of mammals which rules out the possibility of
artifacts caused by electron microscope scanning. The nano-fossils are most
likely smaller parts of larger bacteria explaining the small size.
The McKay team is careful to state that the evidence is
circumstantial and must be examined in context. Each piece of evidence relies on
each other and must be looked at as a whole.
Discovered inside cracks indicated formation
Can form through non-biological process in high
Biological process can still form carbonate
material in high temperatures.
Polycyclic Aromatic Hydrocarbons
Formed by biological process – breakdown of organic
Can form in space, high temperatures and possible
No claim to direct PAHs formation and biological
process. Contamination ruled out by other studies. PAHs found in another
meteorite from Mars – in conjunction with carbon material suggests
Crystal shapes equal to material found on Earth –
through biological process.
Crystals examined were fractured, formed likely by
Three types of crystal shapes, all by biological
process. No evidence of formation by high temperature.
Scanning electron microscope reveals bacteria
Could be fractures caused by the scanning, could
also be mineral grains. They are too small to replicate.
Nano-bacteria can mineralize. Same shaped nano-bacteria
found in mammalian blood rules out artifacts. Smaller nano-bacteria part
of larger bacteria.
The process of examination performed by the McKay team is a
testament to the Scientific Method. Their initial results were carefully laid
out while providing data for any counterpoints, such as contamination (being one
of the main issues). They were careful to announce any “hard facts” and stated
their evidence was circumstantial.
The arguments against the data were presented; the
processes defining the arguments were reasonable, but explainable by rebuttal.
In addition, the data was confirmed by a separate examining group – and this was
even indicated by one of the contender’s papers [R4].
The data presented and the arguments resulting are enough
to demonstrate that life could have existed on Mars. The fact that two
additional meteorites were found to support the results of ALH 84001 corroborate
this. The debate will no doubt continue, and rightly so. It was Carl Sagan who
said “extraordinary claims require extraordinary evidence.” Until Astronomers
find a smoking gun to prove life – which is an extraordinary claim outside the
realm of Earth – the data will most likely be interpreted based on point of view
[R1] Becker, Luann; Popp, Brian; Rust,
Terri and Jeffrey Bada. “The Origin of Organic Matter in the Martian Meteorite
ALH84001.” EPSL. Elsevier. 14 January 1999.
[R2] Gibson, Everett K. and David S.
McKay. “The Case for Relic Life on Mars.” Scientific American, Volume 277, Issue
6, page 58. December 1997.
[R3] Gibson, E.K. et al. “Life on Mars:
Evaluation of the Evidence within Martian Meteorites ALH84001, Nakhla, and
Shergotty.” Precambrian Research. Elvevier. 12 July 1999.
[R4] Knoll, Andrew. “A Martian Chronicle.”
The Sciences. July/August 1998.
[R5] Lunine, Jonathan. Astrobiology. A
Multidisciplinary Approach. Pearson Addison Wesley, San Francisco. 2005.
[R6] McKay, David S. et al. “Search for
Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite
ALH84001.” Science, volume 273. 16 August 1996.
[R7] Thomas-Keprta, Kathie et al.
“Truncated Hexa-octahedral Magnetite Crystals in ALH84001: Presumptive
Biosignatures.” PNAS, volume 98, number 5. 27 February 2001.
[R8] ALH84001: Origins and History:
[R9] Doubts About ALH84001: The JSC Mars
Meteorite Team Responds:
[R10] It’s dead Jim. But was it ever
[R11] Mars Meteorite ALH 84001 – An
[R12] Mars Meteorites:
[R13] Marsnews.com – Life on Mars:
[R14] The ALH 84001 Meteorite:
[R15] What is ALH 84001?
[R16] Evidence for Past Life on Mars?
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