Over the years how many times have you encountered the term ‘primordial soup’ to explain the ferment in which life originated on Earth? The idea of a kind of organic broth in Earth’s early waters, struck by lightning, ultraviolet light, or some other catalyst, and producing slowly but surely the various compounds that eventually take on the characteristics of life – the primordial soup idea has been a foundational metaphor of biology for a long time (81 years). This view on the origin of life has just been seriously challenged.

Just how seriously challenged, we shall see. The new hypothesis was worked out by essentially three people at three institutions: Nick Lane, Department of Genetics, Evolution, and Environment, University College London (UK), John F. Allen, School of Biological and Chemical Sciences, Queen Mary University of London (UK), and William Martin, Institut für Botanik III, Heinrich-Heine-Universität (Germany). Their paper, How did LUCA make a living? Chemiosmosis in the origin of life, will be formally published in the March issue of BioEssays (and is available online now).

LUCA is not a familiar acronym; in biology it stands for Last Universal Common Ancestor, the original form of cellular life. This may, or may not be, the same as the origin of life itself, because that’s a matter of how life is defined. Whether it can be defined with or without a cell structure is just one point of contention. That there is such a thing as a LUCA – a starting point of life within a cell that is the progenitor of all cells we find today, has seemed to be the trend of evidence but remains under dispute. (Dispute here refers to opinions, theories, and hypotheses held by biologists, paleobiologists, biochemists, and other scientists and not the eternal disputations of religious proxies such as Intelligent Design believers.)

Chemiosmosis, also not a familiar word, is at the heart of this paper’s story on the origin of life. Molecular energy, in the form of hydrogen ions (charged protons, both positive and negative), has greater potential energy when one area has more ions than another. The difference between one concentration of ions and another is a proton gradient; and gradients can be increased by separating concentrations of ions with a membrane (in this case, a cell wall). In all living cells, the area outside cell walls has a higher concentration of ions, than within the cell. This relatively high gradient can drive the ions from the high concentration to move toward the area of low concentration. Cell membranes have developed so that selectively ions are allowed through the membrane. As they pass, their potential energy is converted into chemical energy for a key metabolic reaction – the creation of Adenosine Triphosphate (ATP), a universal form of stored energy used by living organisms. This process of allowing ions to pass through a cell membrane to power the creation of ATP is chemiosmosis. (Think chemical osmosis.)

What this paper says is that without chemiosmosis, there is no energy for life. Chemiosmosis does not take place in a soup (technically, a free mixture of organic compounds) because any ions that are present will be more or less evenly distributed throughout the soup. No proton gradient, no energy. So what, during the time at the origin of life, could provide a gradient that would suggest the formation of cell membranes?

Perhaps primordial soup should be replaced with the primordial vent. The paper makes an almost astonishing but plausible leap: Life began in the microscopic cavities found in the lava of hydrothermal vents. This was based on research done by geochemist Michael J. Russell, which showed that a proton gradient exists in these tiny, rocky, ‘cells’ near the volcanic vents in today’s ocean deep. The conclusion drawn is that the organic compounds for life were abundant around the chemically rich volcanic vents, and the micro-cavities provided the cell-like environment – complete with a kind of inorganic chemiosmosis – as a template for the later development of biological cell structure.

Here’s how one of the study’s authors put it:

“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.

[Source: EurekAlert]

The scientists involved with this paper are well aware of its ‘revolutionary’ nature. They don’t seem to shy away from mentioning that the rest of the biology community has ‘primordial soup’ stuck in their heads. So they will not be surprised if their assertions are…picked apart, attacked, challenged, debated. It will be the usual scientific skepticism with perhaps more animus than usual. Fortunately, it seems like their hypothesis can be researched. There are real undersea volcanic vents to explore. The conditions of lava cavities in these vents should be duplicable in the laboratory. There are experts in all aspects of this broad assertion. At the very least it suggests avenues of research that have yet to be taken.

Unless there are some glaring technical or factual errors to destroy the credibility of this original paper, look forward to years of follow-up. It’s science at its most fundamental.