Darwin was right: 'Life began on land, not in sea'

Charles Darwin had suggested that life on Earth originated on land in a "warm little pond" and not in the oceans.  Now, a new study has claimed the theory proposed by the legendary naturalist more than 140 years ago could actually be right. 

The study by researchers at the Osnabruck University in Germany found that the first primitive cells could have germinated in pools of condensed vapour caused by underground hot water or steam bubbling near the surface of the planet.

The findings, published in the journal Proceedings of the National Academy of Sciences, challenging the widespread view that life originated in the sea, the Daily Mail reported.

For their study, the researchers analysed evidence of key rock chemicals in ancient inland and marine habitats and then compared them with a genetic reconstruction of Earth's first cells. They found found that the oceans did not contain the best balance of ingredients to foster life.

Instead the simplest cells assembled in inland hatcheries where -- like the hot springs -- volcanic processes actively vented vapour from the planet's interior, the scientists said.

The chemical composition of these emissions most closely matches the inorganic chemistry of cells. These "cradles of life" share all of the advantages of the deep sea hydrothermal vents that have been previously proposed in the same capacity including the presence of organic matter, they said.

"In addition -- and in contrast to deep sea vents -- terrestrial geothermal fields are conducive to condensation reactions and enable the involvement of solar light as an energy source," said Dr Armen Mulkidjanian who led the study.

However, other scientists claimed that life would have been impossible on surface, as meteorites were bombarding the earth 3.8 billion years ago, and that the surface may not have been hospitable for life.

If this vapour condensed into ponds lined with the right terrestrial minerals the environment would have provided a natural starting point for cells to evolve essential biochemical processes, they pointed out. 

Conceptually similar to the central idea in Darwin's theory, the model in the latest study proposes life on Earth originated on land and subsequently invaded the oceans. In 1871, the legendary naturalist suggested in a letter to English botanist Joseph Hooker that the original spark of life may have begun in "a warm little pond".

Prof Mulkidjanian said under this scenario the ocean was invaded by life at a later stage following the emergence of chemical membranes.

"Geochemical reconstruction shows the ionic (chemical) composition conducive to the origin of cells could not have existed in marine settings but is compatible with emissions of vapour-dominated zones of inland geothermal systems," he said.

"The pre-cellular stages of evolution might have transpired in shallow ponds of condensed and cooled geothermal vapour that were lined with porous silicate minerals mixed with metal sulfides and phosphorous compounds."

The commonly-held belief has been the first microbes originated at the bottom of the ocean in black smoker chimneys formed around deep-sea hydrothermal vents.