New Theory: Earth’s Atmosphere Incubated Life -Not Primordial Soup

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Life on Earth may have originated high up in the atmosphere rather than in the surface waters of oceans or pools, researchers have found. Scientists simulating possible chemical reactions occurring in the upper atmosphere of Titan (above), Saturn's largest moon, found the building blocks of life as we know it — could form without much prodding. A similar process may have taken place on Earth, they said.

Meanwhile, an unrelated study in the journal Nature suggests that Earth's atmosphere had enough oxygen to support complex life forms on the surface as early as 1.2 billion years ago. This study found evidence in ancient sediments in Scotland that the oxygen concentration of the atmosphere was sufficient.

Simulating possible chemical processes in the atmosphere of Titan (image below), Saturn's largest moon, a University of Arizona-led planetary research team found amino acids and nucleotide bases – the most important ingredients of life on Earth.

In an experiment exploring the chemical processes that might be going on in the hazy atmosphere enshrouding Saturn's largest moon, Titan the UA-led team of scientists discovered a variety of complex organic molecules – including amino acids and nucleotide bases, the most important ingredients of life on Earth.

"Our team is the first to be able to do this in an atmosphere without liquid water. Our results show that it is possible to make very complex molecules in the outer parts of an atmosphere," said Sarah Hörst, a graduate student in the UA's Lunar and Planetary Lab, who led the international research effort together with her adviser, planetary science professor Roger Yelle.

The molecules discovered include the five nucleotide bases used by life on Earth to build the genetic materials DNA and RNA: cytosine, adenine, thymine, guanine and uracil, and the two smallest amino acids, glycine and alanine. Amino acids are the building blocks of proteins.

"Evidence of this chemical reaction tells us that the levels of oxygen in the atmosphere were at this key point for evolution, at this much earlier stage in Earth's history," said John Parnell of the University of Aberdeen.

While Titan and Earth aren't exactly twins — the Saturn moon is much colder, with average surface temperatures around minus 290 degrees Fahrenheit (minus 179 degrees Celsius) — they share a thick, nitrogen-rich atmosphere.

And long ago, Earth's upper atmosphere probably looked a lot like Titan's does today, many scientists think, so similar reactions could have taken place here.

"It's pretty likely there was a haze similar to Titan's before life existed," said Horst at the 42nd meeting of the American Astronomical Society's Division of Planetary Sciences, in Pasadena, Calif. "Probably it was a similar kind of gas mixture."

The primordial-soup theory holds that life on Earth took root in the planet's waters. Complex molecules sloshing about in primeval oceans were broken apart and recombined, the theory goes, by some energy jolt coursing through the broth — perhaps lightning strikes. These reactions eventually gave rise to self-replicating molecules: life as we know it.

This may well have happened, Horst said, but her team's results suggest another plausible life incubator: Earth's upper atmosphere.

Big, complicated molecules, some containing 1,000 carbon atoms, are known to exist in the high altitudes of Titan and could have swirled about in Earth's upper air as well. They could have served as starter molecules for all sorts of interesting reactions, Horst said.

Plenty of energy to spur those reactions would have streamed into the upper atmosphere every day from the sun, she added. And high up, there may have been just the right mix of oxygen: enough to be incorporated into some newly forming molecules, but not enough to combust everything.

While we may never be certain how and where life took hold on Earth, studying Titan may help us make some inferences and educated guesses, scientists said.

On Titan, "we know this is happening, and we know we can study it further," said Roger Yelle of the University of Arizona, Horst's Ph.D. supervisor and a member of the research team.

Wherever Earth's first organisms evolved, they were simple and remained so for a long time. Scientists think life first took root around 3.8 billion years ago or so but didn't really explode into a panoply of complex, multicellular organisms until oxygen levels in Earth's atmosphere increased substantially.

Until recently, researchers thought this oxygen boost occurred about 800 million years ago. But the new Nature study suggests that oxygen levels were high enough to support complex life much earlier. The taem found evidence in Scottish rocks that bacteria were using oxygen to generate energy and stay alive 1.2 billion years ago.

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Casey Kazan via University of Arizona and space.com 

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