Proof That Meteors Could Have Sparked Life on Earth
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The simulation, conducted by a team of Japanese planetary materials scientists, produced compounds required to form the first cell and every subsequent organism.
"We use shock experiments to recreate the conditions surrounding the impact of chondritic meteorites into an early ocean," wrote the researchers in Nature Geoscience. "Organic molecules on the early Earth may have arisen from such impact syntheses."
Half a century ago, University of Chicago chemist Stanley Miller showed that lightning strikes in a primordial atmosphere could produce amino acids — the protein-forming building blocks of life.
Those results remain a powerful proof-of-principle for life’s origins, but meteors have replaced lightning strikes as likely catalysts for life-friendly chemical reactions.
Researchers also say that Earth’s atmosphere didn’t resemble the mix of methane, hydrogen and ammonia in Miller’s experiments. A more plausible substrate is a mix of ammonia and water, which composed Earth’s early seas.
"It is easy to produce biomolecules" in an atmosphere like Miller’s, wrote study co-author Yoshihiro Furukawa of Tohoku University. "Our study shows that biomolecules could be produced on early Earth by reactions among meteorites, water and atmosphere."
And four billion years ago, Earth was frequently struck by meteors. Not long after, life emerged.
Furukawa launched his pellets from a propellant gun at 4,500
miles per hour into a stainless steel container of water and ammonia. The impacts generated temperatures of 5,000 degrees
Within this momentary crucible, iron and carbon from the pellets reacted with hydrogen and nitrogen from the ammonia to form fatty acids, amines and an amino acid called glycine. Fatty acids are a component of cell walls, and amines are a basic component of amino acid.
Jack Szostak, a Harvard University chemist who was not involved in the research but has wondered if meteor strikes might produce the chemical requisites of life, called the results "interesting and somewhat encouraging."
"It’s very nice to see some some experimental data in support of that possibility," he said, though he cautioned that more research is needed to extrapolate the results to larger impacts.
"Would we get a lot more organics made, or not so much? In terms of forming protocell membranes, it would be important to form longer-chain fatty acids than were seen in the current experiments," he said.
Furukawa’s team plans to repeat their experiment in other ocean conditions. They are confident, they write, that meteor impacts explain explain the "bulk of organic molecules necessary for life’s origins."
Many explanations, however, may be required.
"Different conditions may have led to the accumulation of a wide array of organic compounds," said Antonio Lazcano, a National
Autonomous University of Mexico biologist and one of the world’s foremost experts on early Earth chemistry.
A former student of Stanley Miller, Lazcano recently revisited one of Miller’s forgotten experiments. Considered a dud at the time, fresh analysis showed that it generated amino acids under conditions that likely existed on primordial volcano slopes.
The building blocks of life "have been reported by simulating drying ponds, hydrothermal vents, volcanic eruptions and collisions of chondrites with the primitive ocean," said Lazcano. "Good!"
Biomolecule formation by oceanic impacts on early Earth [Nature Geoscience]
Images: 1. Visualization of oceanic meteor strikes / Yoshihiro Furukawa 2. Propellant gun / Yoshihiro Furukawa
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