Friday, December 25, 2009

Allen Hill Martian Meterorite Might Provide Proof of Life on Mars in the Past

NASA scientists have produced the most compelling evidence yet that bacterial life exists on Mars.

It showed that microscopic worm-like structures found in a Martian meteorite that hit the Earth 13,000 years ago are almost certainly fossilized bacteria. The so-called bio-morphs are embedded beneath the surface layers of the rock, suggesting that they were already present when the meteorite arrived, rather than being the result of subsequent contamination by Earthly bacteria.

"This is very strong evidence of life on Mars," said David Mackay, a senior scientist at the NASA Johnson Space Center, who was part of the team of scientists that originally investigated the meteorite when it was discovered in 1984.

In a 1996 study of the sample, Dr Mackay and others argued that the microfossils were evidence of life, but sceptics dismissed the claims, saying that similar-shaped structures might not be biological. The new analyses, the product of high resolution electron microscopy, make a strong case for the Allan Hills 84001 Meteorite having carried Martian life to Earth. The microscopes were focused on tiny magnetite crystals present in the surface layers of the meteorite, which have the form of simple bacteria. Some argued that these could be the result of a carbonate breaking down in the heat of the impact.

The new analyses show that this is very unlikely to have resulted in the kinds of structures seen in the rock. Close examination suggested that about 25 percent of the crystal structures were chemically consistent with being formed from bacteria.

"We feel vindicated. We’ve shown the alternate explanation is absolutely incorrect, leading us back to our original position that these structures are formed by bacteria on Mars," Dr Mackay said.

Dennis Bazylinski, an astrobiologist from the University of Nevada who peer-reviewed the findings, said: "Until now I was on the fence but this paper has really thrown out the non-biological explanation." However, he added that the study was not a "smoking gun" for life on Mars. "One meteorite is never going to answer such a complex question," he said.


Allan Hills 84001 (commonly abbreviated ALH 84001[1]) is a meteorite that was found in Allan Hills, Antarctica on December 27, 1984 by a team of US 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.

This rock is theorized to be one of the oldest pieces of the solar system, proposed to have crystallized from molten rock 4.5 billion years ago. Based on hypotheses surrounding attempts to identify where extraterrestrial rocks come from, it is supposed to have originated on Mars and is related to other Martian meteorites.

In September 2005, Vicky Hamilton of the University of Hawaii at Manoa presented an analysis of the origin of ALH 84001 using data from the Mars Global Surveyor and Mars Odyssey spacecraft orbiting Mars. According to the analysis, Eos Chasma in the Valles Marineris canyon appears to be the source of the meteorite.[2] The analysis was not conclusive, in part because it was limited to parts of Mars not obscured by dust.

The theory holds that ALH 84001 was shocked and broken by one or more meteorite impacts on the surface of Mars some 3.9 to 4.0 billion years ago, but remained on the planet. It was later blasted off from the surface in a separate impact about 15 million years ago and impacted Earth roughly 13,000 years ago. These dates were established by a variety of radiometric dating techniques, including samarium-neodymium (Sm-Nd), rubidium-strontium (Rb-Sr), potassium-argon (K-Ar), and carbon-14.[3][4]

It is hypothesized that ALH 84001 originated from a time period during which water may have existed on Mars.[5] Other meteorites that have potential biological markings have generated less interest because they do not originate from a "wet" Mars. ALH 84001 is the only meteorite collected from such a time period.[5]

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.[8]

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