First proposed in 1929 by J.B.S. Haldane in his essay on the origin of life, the "soup theory" suggested that life as we know it was the result of UV radiation converting methane, ammonia and water into the first organic compounds in the early earth oceans. The first cells grew by fermenting this organic primordial soup to generate energy in the form of ATP. Critics of the soup theory have long argued that there is no sustained driving force to make anything react - and without an energy source, there would be no "life". Despite the theory's shortcomings - it has remained the predominant theory in the origin of life debate for more than 80 years.

A paper recently published in BioEssays rejects the old 'Primordial Soup' theory, and proposes that "life arose from gases (hydrogen, carbon dioxide, nitrogen and hydrogen sulfide) and that the energy for first life came from harnessing geochemical gradients created by mother Earth at a special kind of deep-sea hydrothermal vent - one that is riddled with tiny interconnected compartments or pores" said team leader, Dr. Nick Lane of the University College London.

In rejecting the soup theory the team turned to the Earth's chemistry to identify the energy source which could power the first primitive predecessors of living organisms: geochemical gradients across a honeycomb of microscopic natural caverns at hydrothermal vents. These catalytic cells generated lipids, proteins and nucleotides giving rise to the first true cells.

The team focused on ideas pioneered by geochemist Michael J. Russell, on alkaline deep sea vents, which produce chemical gradients very similar to those used by almost all living organisms today - a gradient of protons over a membrane. Early organisms likely exploited these gradients through a process called chemiosmosis, in which the proton gradient is used to drive synthesis of the universal energy currency, ATP, or simpler equivalents. Later on cells evolved to generate their own proton gradient by way of electron transfer from a donor to an acceptor. The team argue that the first donor was hydrogen and the first acceptor was CO2.

Modern living cells have inherited the same size of proton gradient, and, crucially, the same orientation - positive outside and negative inside - as the inorganic vesicles from which they arose" said co-author John Allen, a biochemist at Queen Mary, University of London.

"Thermodynamic constraints mean that chemiosmosis is strictly necessary for carbon and energy metabolism in all organisms that grow from simple chemical ingredients [autotrophy] today, and presumably the first free-living cells," said Lane. "Here we consider how the earliest cells might have harnessed a geochemically created force and then learned to make their own."

This was a vital transition, as chemiosmosis is the only mechanism by which organisms could escape from the vents. "The reason that all organisms are chemiosmotic today is simply that they inherited it from the very time and place that the first cells evolved - and they could not have evolved without it," said Martin.

"Far from being too complex to have powered early life, it is nearly impossible to see how life could have begun without chemiosmosis", concluded Lane. "It is time to cast off the shackles of fermentation in some primordial soup as 'life without oxygen' - an idea that dates back to a time before anybody in biology had any understanding of how ATP is made."

Source: http://www.physorg.com/news184336191.html