|The Universe: Martian Life - ALH-84001
Meteorite May Contain Evidence for
Traces of Life from Mars
Other initial skepticism towards the
biogenic hypothesis focused on the idea that the nanometer-sized
filaments were too small to contain RNA, but evidence continues to grow
that nanobacteria do exist in nature. Furthermore, microbiologists have
successfully cultured nanobacteria in the lab, with sizes within the
range of at least some of the purported microfossils in ALH 84001.
|On August 6th, 1996 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
Under the scanning electron microscope structures were revealed that may
be the remains—in the form of fossils—of bacteria-like lifeforms.
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 in fact fossilized lifeforms, as proposed by the
so-called biogenic hypothesis of their formation, they would be the
first solid evidence of the existence of extraterrestrial life, aside
from the chance of their origin being terrestrial contamination.
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.
Several tests for organic material have been performed on the meteorite
and amino acids and polycyclic aromatic hydrocarbons (PAH) have been
The debate over whether the organic molecules in the meteorite
are in fact of exobiologic origin or are due to abiotic processes on
Mars or contamination from the contact with Antarctic ice on Earth is
Early on, Ralph Harvey of Case Western Reserve University and Harry
McSween of University of Tennessee reported evidence that the carbonate
globules found in the meteorite were formed at high temperature (above
650°C) by volcanic or impact processes on Mars.
At such high
temperatures, it would be very unlikely that the morphology of the
globules could have had any kind of biological origin.
the same authors published papers supporting a hypothesis in which the
globules formed at low temperature from an aqueous solution.
Most scientific papers published in the past 10 years now accept that
carbonates on Mars formed this way.
meteorite caused controversy when analysis revealed the possibility of
fossilized Martian bacteria.
Allan Hills 84001 (commonly abbreviated
ALH 84001) is a meteorite that was found in Allan Hills, Antarctica on
December 27th, 1984 by a team of U.S. meteorite hunters from the ANSMET
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 based on carbonate globules observed.
Under the scanning
electron microscope structures were
revealed that may be the remains—in the form of fossils—of bacteria-like
Some experts argue that the biomorphs found in the meteorite are not
indicative of life on Mars, but instead are caused by contamination by
However, scientists at NASA argue that likely
microbial terrestrial contamination found in other Martian meteorites do
not resemble the texture of the biomorphs in ALH 84001.
the biomorphs in ALH 84001 look intergrown or embedded in the indigenous
material, while likely contamination do not.
While it has not yet conclusively been shown how the features in the meteorite were formed,
similar features have been recreated in the lab without biological
inputs by a team led by D.C. Golden of Hernandez Engineering Inc. in Houston.
David McKay says these results were obtained using unrealistically pure
raw materials as a starting point, and "will not explain many of the
features described by us in ALH84001." According to McKay, a plausible
inorganic model "must explain simultaneously all of the properties that
we and others have suggested as possible biogenic properties of this
In November 2009, a team of scientists at Johnson Space Center,
including David McKay, reasserted that there is "strong evidence that
life may have existed on ancient Mars", after having reexamined the
meteorite using more advanced analytical instruments now available, in
light of the objections that had been made since the biogenic hypothesis
for the biomorphs first had been put forward.
Overall, the team concluded that:
'None of the original features supporting our hypothesis for ALH84001
has either been discredited or has been positively ascribed to
In addition, they argued that since the original paper was published,
the biogenic hypothesis has been "further strengthened by the presence
of abundant biomorphs in other martian meteorites."
The initial analysis of ALH 84001 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. This technique is known as a single blind.
Taunton reported the morphology of the biomorphs in ALH 84001 to be very
similar to terrestrial samples without knowing that she was describing a
Scientific Experiments with Meteorites
Dr. David McKay, Chief Scientist for Astrobiology at the
Johnson Space Center, lectures on his scientific experience with
meteorites, more specifically ALH 84001.
A group of scientists led by David McKay of NASA's Johnson Space Center published an article in the 16 August 1996 issue of Science magazine announcing the discovery of evidence for primitive bacterial life on Mars.
An examination of a meteorite found in Antarctica and believed to be from Mars shows:
1) hydrocarbons which are the same as breakdown products of dead micro-organisms on Earth,
2) mineral phases consistent with by-products of bacterial activity, and
3) tiny carbonate globules which may be microfossils of the primitive bacteria, all within a few hundred-thousandths of an inch of each other.
Astrobiology is a new meta-discipline which combines astronomy,
biology, chemistry, philosophy, and physics in an effort to study the
current state of life in the universe.
In the Stanford Astrobiology Course, lectures follow a, more or less,
linear path from the Big Bang all the way to the development of complex
life and, finally, space exploration.
The course explains how
evolutionary principles have operated at the macro, and micro, level
ever since the birth of the universe we reside in today.