London: Scientists have revealed that life may have existed on Mars thanks to the greenhouse gas carbon dioxide.
The revelation has been made after satellite data suggested huge amounts of CO2 locked in rock four miles under the surface, reports the Sun.
It is thought to be sediment from fizzy carbonated water and suggests that hundreds of millions of years ago the red planet was warmer, wetter and more hospitable to life.
The CO2 in the atmosphere would have kept precious heat in on chilly Mars.
The rock layer is feared to have later been buried by lava as the atmosphere thinned. It was found beside a volcano 750-miles wide called Syrtis Major.
The US experts said the telltale "hint of habitable conditions" was backed by methane being present in the atmosphere at the time.
This could have been caused by "hydrothermal processes in the crust in the presence of carbon dioxide" said Joseph Michalski, of Arizona`s Planetary Science Institute, and Nasa`s Paul Niles in Houston.
But the experts conceded that the surface of Mars was now too cold, dry and acidic for life to exist.