NASA's rover based on the Red Planet could have found the first solid proof that Mars once housed alien life, according to scientists.

As space experts reviewed images taken by Spirit Rover nearly a decade ago, they concluded that NASA have previously overlooked evidence in those images that could point towards bio-signatures for past early forms in outer space in the planet.

Steven Ruff and Jack Farmer of Arizona State University looked at the data from rover's visit to Home plate, a plateau of layered rocks in the Columbia Hills area of the crater. It is an ancient area of eroded volcanic ash thought to still contain an active hot spring, which has formed Silica outcrops, including finger-like formations photographed by the NASA's rover.

Fossils here on Earth are one example of bio-signatures of past life. Stromatolites form when microbes gather into colonies in moist environments, before trapping sediment on the sticky surface. Sediments react with calcium carbonate in the water, making up the limestone.

Stromatolites at El Tatio, which has conditions similar to those on Mars, also formed by hot springs are said to be similar to those pictured by the rover in the Martian crater.

Silica deposits in the structures at El Tatio were found by the team to be almost identical to those found by the Spirit rover in the Gusev crater.

Last month, a separate report by a different team of scientists concluded evidence for life on Mars may have been found as far back as 1976 - but the scientists who suggested it then were not believed.

A review of a study called Viking Labeled Release, which saw two probes land on the Red Planet, brought exciting claims that soil collected from Mars showed microbial life.

The crafts landed 4,000 miles from each other on Mars in the 1970s, but both yielded similarly shocking results following an analysis of Martian soil.

Once the soil had been returned to Earth, they underwent a series of tests including heating them, nutrient injection and being stored in the dark for two months.

Scientists noted that the samples showed signs of microbial life - and were uncannily similar to the same tests on soils from California, Alaska, and Antarctica.