Analysis of a meteorite that fell in the Moroccan desert three years ago revives theories about life on Mars, scientists said on Tuesday.
Scrutiny of cracks in the rock revealed "unique" carbon traces, according to a team led by the Federal Polytechnic School of Lausanne (EPFL) in Switzerland.
The carbon has "a very probable biological origin", the EPFL said in a statement.
"So far there is no other theory that we find more compelling," added Philippe Gillet, director of the school's Earth and Planetary Sciences Laboratory.
The meteorite, named Tissint, plummeted to Earth in front of witnesses on July 18, 2011.
It is one of a handful of rocks believed to have come from the Red Planet, presumably after being knocked off its surface by an asteroid strike and wandering in space before landing on Earth.
The study, published in the journal Meteoritics and Planetary Sciences, contends that liquids containing carbon compounds of biological origin infiltrated the meteorite's "mother" rock at low temperatures.
Their isotopic trace remains today in the fissures, it suggests.
Evidence to support this comes in the ratio of its carbon-13 to its carbon-12 isotopes -- a proportion that, on Earth rocks, matches that of coal, which comes from biological sources.
"Insisting on certainty is unwise, particularly on such a sensitive topic," Gillet cautioned.
"I'm completely open to the possibility that other studies might contradict our findings.
"However, our conclusions are such that they will rekindle the debate as to the possible existence of biological activity on Mars -- at least in the past."
Source: AFP