This past Monday, while most of us were recuperating from 4th of July barbeques and other holiday festivities, Louis Lerman, a geophysicist who is currently a visitor in LBL's Nuclear Sciences Division working on cascade effects, was in Barcelona, Spain, making headlines with a theory that helps explain how life began on Earth.
Reported in the New York Times and other publications, the theory, which Lerman developed as a Hertz Foundation scholar, mostly while at Stanford University, is called the Prebiotic Origin of Organic Molecules or "Pre-BOOM" hypothesis. It asserts that a major role in the creation of living cells was played by bubbles on the ocean surface and their atmospheric counterparts, aerosols and precipitation droplets.
Speaking before a joint meeting of the International Society for the Study of the Origin of Life and the International Conference on the Origin of Life, Lerman described a geophysical framework for the chemical evolution that is thought to have set the stage for biogenesis. This framework, he said, is provided by one of the most fundamental of all the terrestrial processes, the bubble-aerosol-droplet or "bubblesol" cycle.
Under Lerman's proposed scenario, organic material, either from extraterrestrial objects or volcanic eruptions, was dispersed in the sea and air, then adsorbed and concentrated during the formation of underwater bubbles and atmospheric aerosols and droplets. When the bubbles rose to the surface and burst, this organic material was ejected into the atmosphere and carried upward by winds. Atmospheric chemistry, triggered by lightning or ultraviolet radiation, then altered the material into complex organic molecules that precipitated back down to earth as rain and snow, creating more bubbles and starting the cycle all over again.
"The bubblesol cycle on the primordial earth served as a natural reactor for prebiotic chemistry, offering an integrated and cyclic network of microenvironments which strongly supported organic chemical self-organization," Lerman says. "In other words, it may not have been a global primordial soup which was the key to chemical evolution but the primordial bubble."
From the spontaneous generation theory, in which life was thought to arise from nonliving matter, to the theory of panspermia, which maintained that life arrived in spores from outer space, the origins of life on earth has been a source of great debate. Since the 1920s, the prevailing theory has held that life developed through an evolving series of chemical reactions. However, the framework, or mechanism through which this chemical evolution took place has remained a mystery.
"Other people have looked into the chemistry that took place, I've looked at the chemical engineering which enabled the chemistry to occur," Lerman says. "I'm not replacing the details of prebiotic chemistry that have already been worked out. Instead, I'm providing the engineering scaffolding that will allow the specific chemistry at any given stage to go from one level of complexity to the next."
According to Lerman, the engineering requirements for prebiotic chemistry are molecular selectivity, concentration, and stabilization and coordination, plus the availability of energy for synthesis, and cycle-continuity.
"One needs an active and integrated network of chemical reactors to concentrate, stabilize, synthesize and select out organics and certain metals," he says. "On the contemporary earth, the bubblesol cycle plays a predominant role in all of these processes."
Unlike most origin-of-life theories which require broad initial assumptions regarding atmospheric and climatological conditions that existed on the early earth, in postulating his Pre-BOOM theory, Lerman makes only two fundamental assumptions. One, that there was an ocean-atmosphere interface, and two, that there were organic materials somewhere in the atmosphere-ocean regimes.
From these two assumptions, Lerman's theory provides a path for chemical evolution all the way from the reworking of organic compounds to the possible development of protocells.
"Because of its bare minimum assumptions, Pre-BOOM theory provides an almost had-to-have-been framework within which can be placed much of the specialized laboratory experiments and assumed microenvironments of other scientific studies," Lerman says.
For example, mineral substrates and clay have been credited with playing various essential roles in a number of origin-of- life theories. According to Lerman, the bubblesol cycle would have been an ideal means of concentrating minerals and clays and organics at "a common meeting ground."
Furthermore, Pre-BOOM theory provides for a rapid chemical evolution that fits the constraints of the latest origin-of-life time-scale. When chemical evolution was first proposed, the assumption was that the process took place during the first one or even two billion years of earth's history. However, the earliest fossilized remnants of living cells date back 3.5 billion years, which is approximately 300 million years after the time when the earth was heavily bombarded by a shower of small asteroids or comets.
"It is now believed that the chemical evolution had a window of only 10 to 300 million years in which to set the stage for life on this planet," said Lerman. "With this short a time period, one doesn't have enough time to just sit around in warm little ponds and wait for things to happen."
Evidence for Pre-BOOM theory can be observed in phenomena and conditions that exist today, Lerman says. Bubbles, which, at any given moment, cover up to 4 percent of all the ocean surfaces, are known to be highly effective scavengers of organic compounds, salts, metals, and other substances that play a vital role in the chemistry of life. Researchers estimate that sea bubbles deposit anywhere from two to four times the amount of aerosol particles into the atmosphere each year that human industry does.
One of the most intriguing implications of the Pre-BOOM theory is the increased possibility of finding life on other planets. The driving mechanism of the theory -- the bubblesol cycle -- requires only an ocean-atmosphere (liquid-gas) interface that is independent of specific chemical content.
"This suggests that chemical evolution is not so statistically unlikely a process as we have in the past presumed," said Lerman. "Hence we may be considerably more optimistic that the chemical evolutionary prologue to biology has occurred elsewhere in the universe."