"This is the deepest, oldest and hottest marine sediments that prokaryotic life has been found in," John Parks, a professor at the University of Wales who was a co-author, told Reuters.

The microbes were found at 1,626 metres below the seafloor in sediments 111 million years old and at temperatures of 60 to 100 degrees Celsius (140-212.00 Fahrenheit), the report said.

Prokaryotes are microbes lacking nuclei, comprising archaea and some types of bacteria. The lack of cell nuclei distinguishes them from eukayrotes, or all animal and plant life.

"If there is a substantial subsurface biosphere on earth there could also be substantial biospheres on other planets," Parks said, estimating that such microbes could survive temperatures down to about 4 km below the seabed on earth.

"Just taking a scoop from the surface of Mars is not going to tell you whether there is life on Mars or not," he said.

It was unclear if the microbes off Newfoundland had any connection to the sun's energy which is the source of life at the surface -- they might eat buried methane, for instance, formed by compressed plants millions of years ago.

VOLCANIC VENTS

Alternatively, they might be independent of the sun and depend on geochemical energy, like some life forms around volcanic vents on the floors of the oceans. On land, life has also been found deep in mines.

The findings could also complicate plans by many nations and companies to bury greenhouse gases from fossil-fuelled power plants or factories in porous rocks deep below the seabed -- long thought to be devoid of life.

"It's a very risky prospect just putting gases into geological formations and not considering there could be a feedback response because of the organisms down there," Parks said.

It was unclear how microbes might react with carbon dioxide, but Parks said it needed better assessment. The London Convention, which governs dumping at sea, was amended last year to permit storage of carbon dioxide in seabed sediments.

The UN Climate Panel has said that burial of carbon dioxide could be one of the main tools this century to slow global warming that could bring more floods, droughts and rising seas.