An abundance of ancient life in the deep raises the possibility that life may have originated far from the Sun's life-giving rays.
Scientists believe that between 60 to 70% of all bacteria live deep beneath the surface of the Earth with some of the new bacteria identified about 16 million years old.
The research proposing that life originated 400 metres below the seabed was published in a report for Nature magazine.
Co-author John Parkes, of Cardiff University, UK explained their theory.
'There is evidence that life evolved in the deep sediments.
There is clear evidence that life existed more than 3.8 billion years ago. Although, for there to be a big enough biomass for us to detect it in the rocks, it must have been evolving long before that.
But before that time, the surface of the Earth was a brutal place, battered by space rocks and volcanic eruptions.'
So life clearly needed a more kind environment to survive.
'It might be that life was developing in the sub-surface long before [3.8 billion years] where it was protected from meteorite impacts,' he said. 'And as soon as the surface of the Earth became more hospitable, the bacteria were able to move up and colonise it.'
Although evidence of life in ancient rock sediments was found some time ago it is the first time that conclusive proof of live bacteria have been found so deep.
Some of the cells are imbedded in sediments that are many millions of years old, which means they must be ancient, too.
'These bacteria are growing very slowly in the subsurface,' said Dr Parkes. 'They could effectively be immortal.'
Andrew Zilouf
Deep Sea Origin of Life?
Scientists uncover evidence that life may have first evolved in murky deep sea sediments.
