Microfossils in the AH 84001 Meteorite? Since the announcement of possible signs of (fossil) life in the martian meteorite ALH 84001, scientists have put forward many arguments, both in favour of and against this hypothesis. None of them is entirely conclusive and the discussions are still going on. Possible evidence Throughout ALH 84001, there are patches of bright orange carbonates, up to a few millimetres across. A team in the USA, led by Dr David McKay from NASA in Houston, Texas, studied ALH 84001. They found tiny structures in the carbonates that looked like fossilised bacteria. Associated with the carbonates were organic compounds. Although some of the organics are probably terrestrial contamination, a proportion is martian. One particular group of organic compounds, called PAHs, were found in the carbonate in ALH 84001. On Earth, PAHs are produced during alteration of biological remains in sedimentary rocks. Also present in ALH 84001 are crystals of an iron-rich mineral called magnetite. Magnetite can be produced by bacteria. McKay's team reported that the shapes, with their associated organic compounds and magnetite grains, were probably fossilised martian bacteria. Still no firm conclusions This conclusion has not been widely accepted, as PAHs and magnetite have been found in other (non-martian) meteorites, where they have non-biological origins. However, the report of possible fossils in a meteorite from Mars has inspired much research, and re-ignited the debate about life on Mars.

Outline of what are believed to be possible microscopic fossils of bacteria-like organisms found in the meteorite ALH84001.