Discoloured water around a "black smoker"

The discovery was made by researchers at the Carnegie Institution's Geophysical Laboratory in the United States using high-pressure containers.

They found that one of the necessary first steps for life to begin - the conversion of nitrogen to ammonia - may have occurred readily in the regions of the sea floor where superheated water emerges, carrying dissolved minerals.

And, according to the results of the study published in the journal Nature, this suggests that life may have begun in the deep ocean - not at the Earth's surface, as many scientists believe.

Signs of life

Around the deep sea vents can be a thriving community of living things such as clams, shrimps and bacteria that get their energy from the vent and not the sun.

Sometimes the hot water is so discoloured the vents are referred to as "black smokers".

Nitrogen is an essential ingredient of the molecular building blocks of life, amino acids and nucleic acids. But commonplace nitrogen - consisting of two bonded nitrogen atoms - is inert so unlikely to have given rise to life.

Most scientists believe instead that ammonia - three atoms of hydrogen and one of nitrogen bonded together - was required to help life get started. How did nitrogen, then, become ammonia?

The Carnegie scientists suggest that the most likely sites for ammonia production were in the early Earth's crust and in hydrothermal vents. This gave them a vital role in the beginnings of life and in shaping the primitive atmosphere.