Zvi Greenblatt
HET618
Student Number: 1610589
INTRODUCTION .................................................................................................................................. 2
THE CASE FOR LIFE ON MARS OR NOT! ........................................................................... 2
POLYCYCLIC AROMATIC HYDROCARBONS (PAH) .................................................................. 3
The argument for ............................................................................................................................. 3
The argument against .................................................................................................................... 3
MICROFOSSILS ..................................................................................................................................... 3
The argument for ............................................................................................................................. 3
The argument against .................................................................................................................... 3
CARBONATE .......................................................................................................................................... 4
The argument for ............................................................................................................................. 4
The argument against .................................................................................................................... 4
MAGNETITE ........................................................................................................................................... 4
The argument for ............................................................................................................................. 4
The argument against .................................................................................................................... 5
CONCLUSION........................................................................................................................................ 5
REFERENCES ........................................................................................................................................ 6
INTERNET REFERENCES .................................................................................................................... 6
TEXT REFERENCES ............................................................................................................................. 6
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“Sober Creator or Creators Bore”
INTRODUCTION
It must have been a cold day, that 27th December 1984, for even though it was
midsummer, the mean summer temperature in Antarctica is rarely warmer than -15ºC and
had been recorded as low as -35ºC (WEAWEB). Obviously, undaunted by the cold, US
geologist Roberta Score, hunting for meteorites in the Alan Hills region, noticed a
greenish-gray rock against the icy glacial plains and which by its color, she knew was
unique (DISWEB). As the first ‘find’ of the 1984 season, the rock was labeled
ALH84001. Initially, misclassified, the rock languished for ten years until correctly
identified as being Martian in origin (MISWEB). A further two years passed while it was
subjected to detailed analysis. The results of the analysis were designed to be earthshattering in nature and to ensure a maximum audience, the message was further carried
by President Clinton, that NASA scientists had found evidence that strongly suggested
that primitive life may have existed on Mars more than 3.6 billion years ago (DATWEB,
CLIWEB).
This essay will briefly examine the four major assertions made by the discovery scientists
and list the main points and counterpoints for each of the assertions. I will examine in
more detail the assertion that the grains of the mineral magnetite, were produced by
magnetotactic bacteria and provide the arguments that disprove this assertion.
As Carl Sagan once said: “Extraordinary claims, require extraordinary evidence”
(Raeburn, P. pg.184), and these words were echoed by J. William Schopf, who although
invited to the NASA press conference on the discovery, did not share all the views of the
NASA scientists. We have certainly been exposed to an extraordinary claim, but the
extraordinary evidence has not been forthcoming.
THE CASE FOR LIFE ON MARS OR NOT!
NASA scientists, led by David McKay presented four arguments supporting their claim
that Mars once harbored life. These are:
1. Chemical analysis showed that the meteorite contained a number of organic
molecules known as Polycyclic Aromatic Hydrocarbons (PAH), which are known
to be produced by biological processes.
2. Structures were identified within the meteorite which looked remarkably like,
albeit much smaller than Earth-like bacteria.
3. The carbonate minerals have a structure and chemistry that suggest that they may
have been formed with the assistance of primitive, bacteria-like living organisms.
4. Magnetite, a magnetic mineral known to be produced in some Earth based
bacteria, which then align the crystals to form microscopic compasses, was found
in ALH84001.
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Polycyclic Aromatic Hydrocarbons (PAH)
The argument for
Complex organic molecules or PAHs are present in ALH84001. PAHs occur naturally
on Earth and form when living organisms die and decay, thereby creating the
hydrocarbons associated with coal and oil (Knoll A.H. pg.22, Gibson E 1997. pg.10).
PAHs were found deep inside the meteorite, where contamination is very unlikely
(Gibson E 1997. pg.11). Furthermore, terrestrial PAHs were not found in great
concentrations in Antarctic ice and as they are characterized by their own unique
‘fingerprints’, very different from those found in ALH84001, this further mitigated the
chances of contamination (Gibson E 2001. pg.19).
The argument against
PAHs have also been found in Carbonaceous meteorites which formed in the outer solar
system. This means that biological processes are not necessary for their formation (Knoll
A.H. pg.23). During the 13000 years that ALH84001 has been on Earth (Gibson E. 1997
pg.6, McKay D 1996. pg.924), meltwater from countless freeze and thaw cycles could
have permeated the rock, contamination could have occurred. In January 1998, it was
shown that terrestrial amino acids had been found in ALH84001, thereby confirming
contamination by groundwater. When a much younger Martian meteorite, known to have
formed long after liquid water had ceased to flow, leaving Mars lifeless, showed a similar
set of PAHs to those found in ALH84001, researchers concluded that these PAHs came
from non-biological sources (Knoll A.H. pg.23).
Microfossils
The argument for
The discovery-scientists describe structures that look remarkably similar to simple
bacterial cells, except for the fact that they are very small when compared to terrestrial
bacteria by a factor of 10. Arguing that not enough work has been done in determining
the lower size of terrestrial bacteria, support has come from scientists worldwide who are
undertaking various studies to determine that bacteria of this size are viable (Knoll A.H.
pg.23, Gibson E. 1997 pg.12, Gibson E 2001. pg.22).
The argument against
Simple one celled terrestrial organisms are made up of millions of molecules, while the
microfossils are made up of ‘a handful’, thus calling into question the idea that so few
molecules can actually possess the ability to sustain life. In 1998, a National Research
Council panel concluded that the so-called microfossils were “100 to 1000 times too
small to be free-living organisms because they couldn’t have held all the proteins, DNA
and other molecules necessary for even the simplest metabolic processes” (SETWEB).
Knoll also notes that the treatment processes that samples undergo prior to scanning by
an electron microscope, can alter, accentuate or even create the appearances of the
objects (Knoll A.H. pg.23, McKay D 1996. pg.928).
The so-called microfossils could also have been formed by aqueous corrosion on the
mineral surfaces of ALH84001 during its 13000 year exposure to Antarctic ice. It has
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also been reported that some of the elongated structures “resemble the emergent plate
edges of pyroxene” (Gibson E 2001. pg.23).
Carbonate
The argument for
ALH84001 was found to contain tiny globules of calcium carbonate, which is the main
constituent of limestone. The discovery-scientists favored the theory that the carbonate
globules could have a biological origin and were deposited by a fluid, which was
saturated with carbon dioxide that filtered through the rock fractures. Additionally, they
presented evidence that the carbonates formed at temperatures below 100ºC by analysis
of the distribution of the oxygen isotopes in the carbonates (Gibson E 1997. pg.8, Gibson
E 2001. pg.16). The argument concerning contamination on Earth, was countered by
detailed separate analyses of the carbonate globules themselves, which showed no
evidence of contamination (Raeburn, P. pg.184-185, 188).
The argument against
Schopf argues that the globules could have formed by some physical process at a very
high temperature (400ºC-600ºC) during the impact that blasted the rock from Mars. That
would mean that any life in the rock would have been destroyed (Raeburn, P. pg.184).
The high temperature formation model, is also shared by Bradley, McSween, Harvey and
Scott (Gibson E 2001. pg.17). This was found by close examination of carbonaceous
components of unknown origin with δC13 values and isotopic studies of carbon content
consistent with high temperature combustion models (Becker L 1999. pg.72).
Additionally, Carbonate minerals are known to form deep in the Earth at many hundred
ºC in circumstances that no biological influence is possible or apparent. When all the
evidence is summed up, Knoll summarizes the case for carbon quite well when he states,
“…the only valid conclusion is that the carbon precipitates are consistent with the
presence of life – not that they require it” (Knoll A.H. pg.22).
Magnetite
The argument for
I am of the opinion that the discovery of magnetite in ALH84001, represents the
strongest argument supporting the claim for early life on Mars. As such, I chose to
concentrate on this subject in more detail.
Magnetite is a naturally found, magnetic mineral made from oxygen and iron
(MAGWEB). Magnetite has also been found in the brains (and beaks) of certain animals,
(whales, pigeons and salmon), which navigate over large areas. It is presumed that these
animals use the magnetite as a natural compass for navigational purposes by picking up
the magnetic field of the Earth (SALWEB, WHAWEB, PIGWEB, BEAWEB). Certain
bacteria produce extraordinarily small and pure magnetite crystals and then align the
magnetic grains for orientation purposes. As some of the magnetite grains in ALH84001
share the shape, small size and remarkable purity of those produced by bacteria on Earth,
the discovery-scientists argued that Martian bacteria had produced the magnetite.
Additionally, no non-biological process was known that could have formed them (Knoll
A.H. pg.22, SETWEB).
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The basis for the Katie et al. (2000) report, states that the magnetite crystals in
ALH84001 are identical to those produced by the marine magnetotactic bacterium strain
MV-1 and that there is no known natural terrestrial inorganic mechanism that can explain
the magnetite crystals found in MV-1. Supporting evidence comes from the likelihood
that Mars had free standing bodies of water, organic and inorganic carbon sources and a
magnetic field (Kathie L 2000. pg. 2164).
The argument against
Although a strong supporter that the magnetite was produced by living matter, L Kathie
et al. notes that the so called chains of magnetite which are supposedly the orientation
mechanism of the living matter were not observed even though they were observing with
a Transmission Electron Microscope (TEM)( Kathie L 2000. pg. 2166, 2168). She
explains that when the organisms die, the chains collapse as the magnetosome membrane
decomposes and as a result, the magnetite is dispersed. E Gibson et al. reports that the
magnetite in ALH84001 is arranged in chains. Considering the technology available,
there is not even agreement on this basic point (Gibson E 1997. pg 10).
A Knoll points out the magnetite crystals come in various sizes and shapes. This would
imply that there were many magnetite producing microorganisms which would imply a
diverse and complex environment. Additionally, some of the magnetite shows defects in
their crystal structure which are only known to form at many hundreds ºC – way above
livable temperatures (Knoll A.H. pg.22).
Contrary to L Kathie et al. claims, NASA scientists were able to simulate Martian
conditions and create magnetite grains in a non-biological way (inorganically) and also
incorporated them into balls of carbonate (SETWEB).
Edward Scott and David J. Barber present a powerful case that the magnetite in ALH
84001 formed as a result of impact heating and decomposition of carbonate. Their
studies show that “the planes of atoms in the Martian magnetites are aligned with atomic
planes in the carbonate in which the magnetites are embedded” (Scott E.R.D et al. 2002.
pg.1). This means that the magnetites formed in the rock and not inside micro-organisms.
They further argue that if any magnetites with the sizes of the supposedly biogenic
variety had been deposited in the ALH 84001 carbonate prior to the impact heating that
they could not have retained their original properties as they would have acted as seed
crystals during subsequent cooling and would have been coated with new layers of
magnetite. The conclusion is that Martian organisms cannot be responsible for the size
and shape of any magnetite crystal found in ALH 84001 (Scott E.R.D et al. 2002. pg.1,8).
CONCLUSION
One may ask then, if ALH8401 does not show primitive life on Mars, what value has
mankind received from it considering all the time, money and research efforts that have
centered on this little piece of Mars? Certainly, many scientists have been attracted to
this field of research and they have forced us to critically examine all our approaches,
scientific, moral and philosophical to extraterrestrial samples. Many of the same
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processes used to discount life forms in ALH84001, will be used to help us answer the
age old question: ‘Are we alone?’
As we plan for sample return missions from Mars, we are refining our scientific methods
to better understand fossilization processes in anticipation that these samples will give us
the key to understanding the origins of life on Earth, Mars and perhaps other planets.
Therein lies ALH84001’s value, and it is likely to increase over time.
REFERENCES
Internet References
BEAWEB:http://news.nationalgeographic.com/news/2004/11/1124_041124_magnetic_bi
rds.html
CLIWEB: http://www.coseti.org/mars_2.htm
DATWEB: http://www.spie.org/web/oer/december/dec96/etlife.html
DISWEB: http://www.ovpr.uga.edu/researchnews/summer2001/mars.html
MISWEB: http://curator.jsc.nasa.gov/antmet/marsmets/samples.cfm
MAGWEB: http://www.mindat.org/min-2538.html
PIGWEB: http://www.can-do.com/uci/ssi2000/pigeons.html
SALWEB: http://jeb.biologists.org/cgi/content/abstract/140/1/51
SETWEB: http://www.seti.nl/article.php?id=2009
WEAWEB: http://www.antarcticconnection.com/antarctic/weather/index.shtml
WHAWEB: http://www.afsc.noaa.gov/NMML/education/cetaceans/cetaceastrand.htm
Text References
Becker, L et al The origin of organic matter in the Martian meteorite ALH84001 in Earth
and Planetary Science Letters167, January 1999
Gibson, E.K. et al The Case for Relic Life on Mars in Scientific American,December
1997, Vol.277 Issue 6
Gibson, E.K et al Life on Mars: evaluation of the evidence within Martian meteorites
ALH84001, Nakhla, and Shergotty in Precambrian Research 106 (2001), Pages 15 -34
Kathie L.T et al Truncated hexa-octahedral magnetite crystals in ALH84001:
Presumptive biosignatures in PNAS Vol. 98 Number 5 February 27th 2001
Knoll, A.H. A Martian Chronicle in The Sciences. July/August 1998, Pages 20 – 26
McKay D.S. et al Search for Past Life on Mars: Possible Relic Biogenic Activity in
Martian Meteorite ALH84001 in Science, August 16 1996
Raeburn, P. Uncovering The Secrets Of The Red Planet: Mars 1998. The National
Geographic Society. Washington DC
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Scott E.R.D and Barber D. J Resolution of a Big Argument About Tiny Magnetic
Minerals in Martian Meteorite May 13th 2002 downloadable from
http://www.psrd.hawaii.edu/May02/PSRD-ALH84001magnetite.pdf
Authors note: The words ‘Sober Creator’ and ‘Creators Bore’ are anagrams of ‘Roberta
Score’, the discoverer of ALH84001.
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