Richard A Lovett
Life may not have originated in the primordial soup of an ancient pond, according to scientists, but rather in a “nuclear geyser” powered by an ancient uranium deposit.
Shigenori Maruyama of Tokyo Institute of Technology says the idea came from what chemists know about crucial compounds in our own bodies.
Many of these compounds – including DNA and proteins – are polymers formed from chains of smaller building blocks.
Each of these molecules serves a different purpose in the body, but something they all have in common, says Nicholas Hud, a chemist from Georgia Institute of Technology, Atlanta, is that a molecule of water is released when each new building block is added.
“There is a theme here,” he said last week at a NASA-sponsored symposium on the early solar system and the origins of life. To a chemist, this suggests that these biopolymers must have originated under relatively dry conditions.
Otherwise, Hud says, the presence of water would have forced the reactions to run backwards, breaking chains apart. But, there’s a problem: most scientists assume life started in water.
The solution to this paradox, according to Hud, comes from realizing that water comes and goes. The major chemicals of life, and presumably life itself, may have formed in an environment that was alternately wet and dry. “It could be seasonal,” he says. “It could be tides. It could be aerosols that go up [into the air] and come back down.”
Some prebiotic chemical reactions occur easily at moderate temperatures, but others, says Robert Pascal, a physical organic chemist from the University of Montpellier, France, require a more concentrated source of energy. This energy may have come from the sun, which in the early solar system was considerably more active than today. But another source is radiation.
Which brings us back to nuclear geysers.
Based on analyses similar to Hud’s and Pascal’s, Maruyama has identified nine requirements for the birthplace of life. One place where all can occur at once, Maruyama says, is in the plumbing of a nuclear geyser.
This would not only produce heat to power the geyser, but produce radiation strong enough to break the recalcitrant molecular bonds of water, nitrogen, and carbon dioxide, all of which must be cleaved in order to produce critical prebiotic compounds. Periodic eruptions of the geyser would also produce alternating wet and dry cycles, and water draining from the surface would bring back dissolved gases from the atmosphere. The rocks lining the geyser’s subterranean channels would provide a source of minerals such as potassium and calcium.
“This is the place I recommend [for the origin of life],” Maruyama says.
Once life originated, he says, it would have been spewed onto the surface and from there into the oceans. From there, it spread to every known habitable niche on the modern Earth.
Extraterrestrial life (or at least life as we know it), he says, would need similar conditions in which to originate.
That, he thinks, means the best place to look for it in our solar system is Mars. However habitable the subsurface oceans of outer moons such as Ganymede, Europa, and Titan may be for bacteria, they likely lack the conditions needed for the origin of life as we know it, he says.
As for exoplanets? Similar conditions are also needed there, he says, including not only an energy source to power pre-biotic reactions, but a “triple junction” between rock, air, and water, where all the needed materials can come together simultaneously.
