Researchers have “resurrected” a 4 billion-year-old protein that may shed light on how life evolved on Earth.

The findings published in the journal Structure describe how a certain class of proteins called thioredoxins probably existed in the most primitive life forms.

“So far, attempts to understand protein structure evolution have been based on the comparison between structures of modern proteins. This is equivalent to trying to understand the evolution of birds by comparing several living birds," senior study author Jose Sanchez-Ruiz of the University of Granada said in a statement.

Since fossils are one of the best resources for understanding how life evolved, scientists decided to recreate fossil proteins in a laboratory and analyze their features. Thioredoxins were chosen because they are found in organisms from the three domains of life: bacteria, archaea and eukaryotes.

The research team took previously resurrected Precambrian proteins and found they resembled those that existed when life began, proving that protein structures remain constant over extended periods of time.

"The putative ancestral structures reported here are consistent with the thioredoxin fold being an approximate 4 billion-year-old molecular fossil of sorts and confirms that protein structures can evolve slowly," Sanchez-Ruiz and his colleagues wrote in the study.

Not only that, the protein was exceptionally stable, was able to bind with different chemicals and could function in highly acidic environments.

"That makes a lot of sense, because 4 billion years ago many people think that the temperature was high and the oceans were acidic," Sanchez-Ruiz told LiveScience.

Researchers also tested the protein to see how well it coped with heat. "We have looked at a number of gene families now, and for all of them we find the most ancient proteins are the most thermally stable. From this, we conclude that ancient life lived in a hot environment," Eric Gaucher, a professor at Georgia Tech who helped with the study, told the BBC.

Since the proteins are re-creations, scientists can’t be certain they are exact replicas of the originals. "There is no way to make absolutely certain unless we invent some kind of time machine," Sanchez-Ruiz said. "But we know that the properties we measure for these proteins are consistent with what we would expect of 4 billion-year-old proteins."

Another possibility, not mentioned in the study, is that the ancient protein lived on another planet -- maybe Mars.

"Four billion years ago, Mars was a much a safer place than Earth. Maybe we have resurrected Martian proteins. Maybe the last universal common ancestor (the first life) formed on Mars and transferred to Earth," Sanchez-Ruiz told the BBC.

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