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.

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.