HOUSTON -- The case for life on Mars, albeit in the very distant past, was strengthened by a new report on March 20 that a Martian meteorite contains crystalline traces of living organisms.
The assertion that the meteorite from Mars known as ALH 84001 shows evidence of life, first ventured by a team of scientists in 1996, remains controversial. But no evidence has refuted it, and new findings make it more difficult to find a nonbiological explanation, several scientists said.
The most significant new evidence is that the rock contains crystals of magnetite that have a shape only found in magnetite produced by living organisms.
While magnetite grains can easily be produced by nonliving chemical processes, none of those have ever been found to have the six-sided columnar shape seen in these grains, said Kathie Thomas-Keprta, a coauthor of the original paper reporting evidence of life in the Martian meteorite.
"We found a variety" of shapes of magnetite crystals in the meteorite, Thomas-Keprta said. But the unusual hexagonal forms, she said, "are produced by bacteria in anaerobic [oxygen-free] environments. We don't know of any nonbiological process" that can produce such shapes, she said.
Magnetite crystals found in the Mars meteorite match those found in microbes on Earth "in size, shape, chemistry, and the lack of structural defects," she said.
According to Thomas-Keprta, one of her coauthors on the new research, Dennis Bazylinski, has been doing research on the magnetite grains in microbes for 20 years and has never found any such forms being produced nonbiologically. The unusual crystals appear in such quantities, Thomas-Keprta said, that she stopped counting after she documented over 100 of them.
"We think that's our strongest evidence," McKay said of the new magnetite research. And unlike some other possible signs of life that critics have said might be contamination that entered the rock on Earth, the magnetite grains are incorporated in the rock and clearly came from Mars.
The findings were reported at the annual Lunar and Planetary Science conference held at the Johnson Space Center.
In 14 talks and dozens of poster presentations at the conference, scientists on both sides of the contentious debate over the significance of the Martian meteorite presented their latest results, but none appeared to significantly undermine the original assertions of possible biological remains in the rock.
[See http://www.boston.com/dailyglobe/globehtml/080/ for full text.]
Back to document index
Original file name: CNI - Mars Meteor.Life
This file was converted with TextToHTML - (c) Logic n.v.