The journal “Science”, reported in its August 1996 issue, that life had been found on Mars. Or more accurately, proof of ancient life had been found inside a Martian meteorite that fell to Earth.
A combined research team of scientists from the NASA research center and Stanford University, revealed that fragments of a meteorite identified as Martian in origin, had mineral features consistent with biological processes, and what appeared to be microscopic fossils of primitive organisms resembling bacteria. Their estimate for when this “life” existed? Over three billion years ago.
The team determined the meteorite’s origin from the composition of the fragment, and the gases trapped inside, which match those of the planet Mars, as measured during the Viking mission. At that time, gases in the atmosphere were identified as being completely different from those found on Earth, Venus, and all other identified sources.
Known as AHL 84001, it was located in Antarctica in December of 1984. Weighing in at 4.75 lbs, it resembled a rounded brick or potato with a glassy, black exterior called a fusion crust, from entrance through Earth’s atmosphere. AHL 84001 is likely the result of Martian volcanic activity, and is very similar to igneous rocks formed from that kind of activity on Earth.
But volcanic activity alone, would not have propelled it into space. It would require an escape velocity of about 11,000mph to leave the Martian surface. The only known natural source that could put that much force behind the fragments, would be the impact of an asteroid, whose size as estimated by scientists, would have to be over a mile in diameter. From its initial jettison into space, the meteorite would have gone into orbit around the sun, a pattern that would be tugged and pulled in different directions by passing near to Mars and the influence of larger planets such as Jupiter. Eventually it would have come within the pull of Earth’s gravity, and plunged to the ground.
Dr. David McKay and colleagues, authors of the “Science” paper, presented their case for “life” within the meteorite, by noting the presence of carbonate mineral globules, which they see as having formed from liquid water infiltrating the rock. Since life cannot exist without liquid water, the presence of these globules was crucial to their theory. Having estimated the birth of the meteorite at over 3 billion years ago, it is surmised that at that time Mars may have had a very different atmosphere, one capable of supporting some kind of life form, as opposed to the cold, barren desert the planet is today. Countering the origin of the globules is the evidence of other scientists, that carbonate mineral can form under extreme heat, which would make life insupportable. However, even they acknowledge that the high heat needed to form the globules could very well have been from bacterial activity, which has the unusual ability to form minerals where science would not expect to find them.
The McKay team’s findings were based on three criteria, each of which they admitted could have other origins when taken separately, but “when they are considered collectively, particularly in view of their spatial association, we conclude that they are evidence for primitive life on Mars.”
Their first pieces of “evidence” were the elliptical, rope-like structures found in cracks of the carbonate mineral globules. They measure 20-100 billionths of a meter across, and can only be seen with an advanced electron microscope. The team was very careful to present proof that the shapes were similar to recognizable bacterial forms found on Earth, but were part of the meteorite and had not been introduced into the rock while it lay in the Antarctic or in the laboratory. Dr. W. Schopf, a renowned paleontologist and expert on Earth’s early life forms, noted that the shapes might not be bacteria, since inorganic sources can produce the same formations. Before accepting them as fossils, Dr. Schopf suggested that he would need to see evidence of the cell walls which keep bacteria separate from their environment, budding or dividing to indicate reproduction, and evidence of growth in a range of sizes as well as colonies of cells.
The second piece of evidence, was the identification of microscopic mineral grains in the carbonate mineral globules. McKay’s team suggests they were produced by bacteria on Mars, but acknowledge that such grains can be non-organic in origin. Still, they maintain that (A) they were formed on Mars, (B) in all respects, they resemble biologically produced mineral grains on Earth, and (C) that even were the mineral grains and the larger crystals they were found in, inorganic in origin, they could not have formed without some assistance from “life”. One of their strongest arguments to support the last point, are the groupings of iron oxide mineral, and iron sulfide mineral, which lay in patches of magnesium carbonate with a porous appearance. They contend that such groupings are the result of a biological process.
The last piece of evidence is one not familiar to non-chemists. It involves PAHs, or polycyclic aromatic hydrocarbons- a group of chemicals with similar structures. Again, they were faced with the fact that while PAHs can be formed during the decomposition of bacteria, they are also formed by non-organic means. McKay’s approach was to prove that the PAHs were consistent with the decomposition of elementary bacteria, and were not laboratory contamination, contributions from the Antarctic environment, or the same as PAHs found in meteorites of non-organic origins.
Despite the intensity of their studies, the findings were, and still are disputed. Until a space mission successfully lands on Mars and returns with rock that is identical in content to that studied by McKay, the debate will go on. Perhaps even after, unless those futuristic “samples” can tell us whether their elements were formed by life or accident.
McKay and colleagues have never contended that there is life on Mars, but that life did exist in the very ancient past. So far, nobody has been able to dispute him.