Survival
Above: The Sun setting on Mars, photographed by Curiosity rover on Sol 956 (Earth: April 15, 2015)
A Martian 'Great Dying'?
It is impossible for life to have originated on Mars as we know it today. The conditions are too bleak.
Mars had an ocean and a thicker atmosphere in ancient times. Life might have appeared then.
However, at some point in prehistory a planetary disaster happened to Mars, the nature of which is still unknown.
The only way in which life on Mars could be present today would be if it had evolved billions of years ago, before Mars lost its surface water and most of its atmosphere. At the same time, Mars lost nearly all of its magnetosphere, allowing deadly solar radiation to reach the surface.
Only the hardiest life that existed at that time could have survived. Any present-day Martian life is clinging to existence in a harsh, cold, and arid ecological niche.
It appears that there is not even rudimentary vegetation on Mars, not even mosses or lichens. We might therefore reasonably infer that any life on Mars would have to be carnivorous (feeding on prey, carrion, or both).
A land-based carnivorous ecosystem would accord well with survival requirements for nearly all terrestrial reptiles. The only omnivorous reptiles are iguanas and their cousins the argamas.
Millions of years before a cometary impact wiped out the dinosaurs, 96 per cent of all life on Earth was killed by a still-unidentified environmental catastrophe referred to as the Permian-Triassic extinction event, .
The average temperature of the oceans reached 40 degrees celsius and all surface water was rendered toxic and flammable with huge concentrations of hydrogen sulfide. Oxygen almost disappeared from the atmosphere: It was replaced by suffocating carbon dioxide.
Earth became more poisonous than Mars is today.
The Permian-Triassic event is known as 'The Great Dying'.
But life on Earth did not end.Every animal on the planet today is descended from the four per cent of creatures that survived The Great Dying.
The chief survivors were the early reptiles known as diapsids. They were the ancestors of the dinosaurs who went on to dominate Earth for millions of years. Later still, the diapsids also survived the extinction of their dinosaur descendants. They are still going strong: we know them as lizards, snakes, and crocodiles.
There have been at least five global extinction events in Earth's history. And each time, life came crawling back from the brink. The evidence of our own planet very strongly suggests that once life has got a foothold, it is practically impossible to eradicate.
Why, then, should we expect all lifeforms to have become extinct during a Martian 'Great Dying'?
Reptile-like lifeforms that appeared in the habitable early history of Mars would be the likeliest candidates to have survived a planetary disaster and to have persisted to this day.
And perhaps a handful of NASA photographs shows that they have.
Above: One of the NASA photographs that led to the discovery of flowing water on Mars
Left: Martian topography (red=high; blue=low)
Right: NASA illustration of the now-vanished ancient North Martian Ocean
Right: NASA illustration of the now-vanished ancient North Martian Ocean