FIVE months after Nasa scientists stunned the world with supposed evidence of past life on Mars, British microbiologists have discovered features on a chip of Martian meteorite that add weight to NASA's claims.

Andrew Steele and his team at Portsmouth University say their meteorite sample displays similarities to those which first excited Nasa. This runs counter to evidence last month from groups of scientists in the United States that Nasa's claims were bogus.

In Britain, scientists at Edinburgh, Manchester, Portsmouth and the Open universities, and at the Natural History Museum in London, are analysing their own tiny samples of meteorite.

The Portsmouth team is using atomic force microscopes, which can see objects only several atoms across, to study chips from meteorite ALH84001 which is thought to have broken from the surface of Mars some 15 million years ago.

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While Nasa's scanning electron microscopes require the samples to be coated with a metallic film before they can be analysed, Portsmouth microscopes can see them in their natural state.

The high-resolution images seen by Nasa were attributed by some critics to the gold-palladium coating. Nasa has suggested that these are fossilised bacteria.

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Dr Steele says he has seen similar 150-nanometre blobs on the surface of a sample, again and again. "We are seeing structures that NASA is very delighted to see. To my knowledge, no one else has seen these surfaces without coating," he said.

Teams at Manchester and Edinburgh universities are also working on chips from the same potato-sized Martian meteorite, trying to date the carbonate globules found in it and to determine the temperature at which these were deposited.

Previous work at Manchester, using potassium-argon dating, had suggested that a potassium-bearing mineral found next to the carbonate, was 3,800 million years old.

Team leader Grenville Turner said that some scientists had assumed the chemical composition of the carbonate showed it had been deposited from hot fluids at temperatures sufficient to ensure that this was its true age.

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The team is looking at evidence that the carbonate may have been deposited cold. If this is the case, the carbonates may well be much younger and therefore formed in conditions less favourable for life.