The most famous Martian “chip off the old block,” that is, the ALH84001 meteorite, was discovered a quarter-century ago in Antarctica. The meteorite is believed to have been ejected from Mars about 17 million years ago and, and much like the aliens from John Carpenter’s 1980s remake of the sci-fi classic The Thing, spent close to 11,000 years encased within Antarctic ice sheets. Though not as exciting as Carpenter’s alien shape-shifter, possible fossil remains of microorganisms observed in samples taken from the meteorite set the scientific world ablaze upon their discovery. Now, new evidence suggests that these strange fossil formations “are almost certainly fossilized bacteria.”

As reported yesterday by the UK’s Times Online, “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.”

David Mackay, a senior scientist at the Nasa Johnson Space Centre, calls the new discovery “very strong evidence of life on Mars.” Mackay was part of the team of scientists that originally investigated the meteorite when it was discovered in 1984.

The discovery of microorganisms was partially due to the presence of other indicative factors. Earlier NASA tests on ALH84001 first revealed a form of magnetite, only found in the presence of certain minute microorganisms as observed here on Earth, to be prolific throughout the meteorite. Later, further analysis would indicate that “structures” which resembled fossilized bacteria consistent in size and shape with controversial “nanobacteria” believed to exist here on Earth were also present. At that time, it had not been ruled out that the apparent bacteria might be terrestrial in origin, however.

Twenty five percent of the crystal structure found within the meteorite, even as far back as 1996, appeared to have been the result of bacterial byproducts. “We feel vindicated,” Mackay says. “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.”

Two other Martian samples exist; The Nakhla meteorite, recovered on June 28, 1911 near Nakhla, Alexandria, Egypt, as well as the Shergotty meteorite, which fell to Earth on August 25, 1865 in India, where it was promptly collected by locals. Features in each of the three samples suggest remnants of biofilm and their associated microbial communities.