The site of their discovery is a hot spring more than 9,000ft under the Atlantic Ocean where a volcanic vent pours out hydrogen and provides conditions for the very earliest forms of life to thrive.

The experts say life may even now be springing into existence there now.

When life first appeared on earth 3.5 billion years ago the planet had no oxygen.

It has long been believed that hydrogen was the key then to unlocking the door of life.

The discovery of the hydrogen "black smoker" in the Rainbow hydrothermal field on the North Atlantic ridge has now provided the first concrete evidence to support the theory.

Microbes that feed on hydrogen have been found before in the hot water around hydrothermal vents, but never in a place with so much potential for life.

The Rainbow smoker, 3,500m deep and 200m wide, produces large quantities of the gas which is given off as a result of seawater reacting with rock dredged up from deep below the Earth's surface.

Major breakthrough

Scientists investigating the origins of life on Earth and possibly on other planets see the discovery as a major breakthrough.

Professor Joe Cann from the University of Leeds said: "Hydrogen has been a hot suspect for the origin of life and now we have a place in the modern world where life could originate and perhaps is originating now."

Life probably started with organic chemicals forming into amino acids, the basic components of living things, from which the first hydrogen-consuming microbes emerged.

But Prof Cann said any of these microbes being newly created around the Rainbow vent would instantly be snapped up by other higher forms of life that teem around black smokers.

Describing the findings for the first time at the British Association Festival of Science at Cardiff University, Prof Cann said: "The most primitive organisms on earth are hydrogen oxidising microbes.

"That's why we think life originated in a hot hydrogen environment. Now the discovery of this hydrogen-spewing black smoker makes the theory much more plausible."

It was a British scientist, Chris German, from the Southampton Oceanography Centre, who first spotted the plume of high temperature water that led scientists to the smoker.

A French submersible dived down and discovered the vent in the summer of last year.