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Friday, 12 February, 1999, 14:37 GMT
Martian 'bacteria' matched to Earth
Mars
The Martian microbe claim caused a sensation
By BBC News Online Science Editor Dr David Whitehouse

Unusual features found on a Martian meteorite may be those of fossilised alien bacteria after all, research suggests.

When Nasa scientists first made their claims about Martian microfossils in 1996 they were greeted with scepticism by those who believed the shapes were too small to have come from any bacteria-like organisms.

But in a new study, scientists have shown that certain parts of Earth bacteria can also leave similar remains when they are fossilised.

"We believe we have clearly shown that features similar in size and shape to those in the Martian meteorite do exist within the biological record on Earth," said Kathie Thomas-Keprta, of the Lockheed Martin Space Mission Systems and Services in Houston, Texas.

But she warned that this does not prove definitively that the meteorite features are fossilised organisms.

Fossilised filaments

The Earth bacteria, taken from rocks in Washington State, were bred in conditions that simulated the environment deep beneath the Earth's surface. When they died, they became fossilised in only eight weeks.

ALH84001
ALH84001L: The source of the controversy
Scientists saw that about 30% of the microbes grown in the laboratory had filaments attached.

Crucially, filaments that were not attached to the organisms also became fossilised. Researchers say it is the first time such tiny parts of bacteria have been shown to become mineralised in the same way as a whole microbe.

The work suggests the structures on the Martian rock may also be the fossilised remains of filaments.

Original findings

The longest shapes identified on the meteorite are approximately 1/25 the diameter of a human hair. Dr Everett Gibson, a Nasa planetary scientist who worked on the meteorite, said the new study supported the original findings.

Mars
It is believed water once flowed on Mars
ALH84001, the potato-sized Martian meteorite, is about 4.5 billion years old. It is thought to have originated beneath the Martian surface.

Current theories suggest Mars was warmer and wetter billions of years ago. The water is believed to have penetrated fractures in the surface rock, forming an underground water system. This system may have been the best location for life during much of Martian history.

The Earth bacteria used in this new experiment came from the Columbia River basalt of Washington State. They are an example of life thriving at depth in fractured rock where it is isolated from light and protected from any harsh environment at the surface.

So it may be a good example of what life was like on Mars.

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See also:

22 Jan 99 | Sci/Tech
The source of Martian water
10 Aug 98 | Sci/Tech
Red planet rock
13 Dec 98 | Sci/Tech
Rain check on Mars
22 Oct 98 | Sci/Tech
New hope of finding life on Mars
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