Billions of years ago, the theory goes, the earth was a forbidding, completely lifeless place, scorched by ultraviolet rays, smashed by asteroids, wracked by geothermal activity, and zapped by lightning.
And somewhere in the “primordial soup” of the ancient ocean, a chance chemical reaction brought together the ingredients to make the building blocks of life.
Now, researchers from MIT are suggesting the big moment may not have happened in the ocean. It could have happened in a shallow pond, perhaps 4 inches deep.
The researchers say in a new study such a pond could have held high concentrations of a key ingredient, nitrogen, while that would have been less likely in the ocean.
“Our overall message is, if you think the origin of life required fixed nitrogen, as many people do, then it’s tough to have the origin of life happen in the ocean,” the study’s lead author Sukrit Ranjan, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences, said in a statement. “It’s much easier to have that happen in a pond.”
Ranjan and colleagues from MIT, Harvard University, and Cambridge University published their results earlier this month in the journal Geochemistry, Geophysics, Geosystems.
The researchers said nitrogen oxides were likely deposited in bodies of water, including oceans and ponds, after lightning broke the strong bonds between pairs of nitrogen atoms in the atmosphere.
Lightning “produces enough energy that it breaks that triple bond in our atmospheric nitrogen gas, to produce nitrogenous oxides that can then rain down into water bodies,” Ranjan said.
The theory has been that the nitrogen oxides fell into the oceans and were relatively stable. But the new study suggests that there were two “sinks” that could have reacted with, and reduced, the amount of nitrogen oxides in the ocean.
One was the ultraviolet light from the sun and the other was the dissolved iron that came from primitive oceanic rocks.
“We showed that if you include these two new sinks that people hadn’t thought about before, that suppresses the concentrations of nitrogenous oxides in the ocean by a factor of 1,000, relative to what people calculated before,” Ranjan said.
Life would have a better chance in ponds, he suggested. The ponds could have been 4 to 40 inches deep.
“The picture that’s emerging is that overall, many prebiotic synthesis pathways seem to be chemically easier in ponds than oceans,” he said.
The study’s abstract said its findings “inform the kind of prebiotic chemistries that would have been possible on early Earth,” but also noted the need for further studies to “reduce the considerable uncertainties in predicting [dissolved nitrogen oxides] on early Earth.”
Scientists have been pursuing for decades the theory of abiogenesis, the idea that life arose from non-life as chemicals on a forbidding early Earth were roiled by ultraviolet rays, geothermal activity, asteroids, and lightning.
In 1953, the American chemists Harold C. Urey and Stanley Miller produced simple organic molecules including amino acids, when they combined warm water with a mixture of water vapor, methane, ammonia, and molecular hydrogen, while sending electrical discharges through the artificial “atmosphere.” But creating simple life in a lab has turned out to be more difficult than originally thought.