Life 'began on the ocean floor'

It may all have begun next to hydrothermal vents in the deep sea

By Dr David Whitehouse BBC News Online science editor

A new and controversial theory on the origin of life on Earth is causing a stir among scientists.

And one of the implications is that life could be more likely on planets where it was previously thought unlikely to flourish.

The theory claims that living systems originated in so-called "inorganic incubators" - small compartments in iron sulphide rocks.

Proposed by Professor William Martin, of Düsseldorf University, and Professor Michael Russell, of the Scottish Environmental Research Centre in Glasgow, it stands conventional ideas on their head.

Instead of the building blocks of life forming first, and then forming a cell-like structure, the researchers say the cell came first and was later filled with living molecules.

In total darkness

Since the 1930s, the most accepted theory for the origins of cells and therefore of life, claims that chemical reactions in the Earth's most ancient atmosphere produced the building blocks of life which led to the first cells.

In explaining their new theory Professors Martin and Michael Russell outline their problems with the existing hypotheses of cell evolution.

Rather than the building blocks of life originating first and then forming themselves into cells they believe that cells came first.

They say that the first cells were not living cells but inorganic ones made of iron sulphide and were formed not at the Earth's surface but in total darkness at the bottom of the oceans.

Life, they add, is a chemical consequence of convection currents through the Earth's crust and, in principle, this could happen on any wet, rocky planet.

Solar system

Dr Russell says: "As hydrothermal fluid - rich in compounds such as hydrogen, cyanide, sulphides and carbon monoxide - emerged from the Earth's crust at the ocean floor, it reacted inside the tiny metal sulphide cavities.

"They provided the right microenvironment for chemical reactions to take place. That kept the building blocks of life concentrated at the site where they were formed rather than diffusing away into the ocean. The iron sulphide cells, we argue, is where life began."

One of the implications of this idea is that life on other planets or some large moons in our own solar system, like ice-crusted Europa - a moon of Jupiter - might be much more likely than previously assumed.

The research is published in the Philosophical Transactions of the Royal Society.