The Universe: Martian Life - ALH-84001
Meteorite May Contain Evidence for Traces of Life from Mars



 
The Universe: Martian Life - ALH-84001
Meteorite May Contain Evidence for Traces of Life from Mars

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 NASA.

Under 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 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.

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.

Several tests for organic material have been performed on the meteorite and amino acids and polycyclic aromatic hydrocarbons (PAH) have been found.

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 still ongoing.

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.

Later, however, 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.

 
A 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 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 based on carbonate globules observed.




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. 

Under the scanning electron microscope structures were revealed that may be the remains—in the form of fossils—of bacteria-like lifeforms


Some experts argue that the biomorphs found in the meteorite are not indicative of life on Mars, but instead are caused by contamination by earthly biofilms.

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.

In particular, 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 meteorite."

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 non-biologic explanations.'


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 Martian meteorite.


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.