Evolution May Have Been Faster for Early Life Forms on Earth

“At the higher temperatures that seem to have prevailed during the early phase of life, evolution was shaking the dice frantically.”

Life arose at a time when Earth was much hotter than it is today. According to a new study published in the Proceedings of the National Academy of Sciences, those high temperatures may have fuelled rapid evolution of early life forms.

Researchers from the University of North Carolina, Chapel Hill, found that the rates of spontaneous mutation in DNA — a key driver of evolution — rise very steeply as temperatures increase.

When the planet formed about 4.6 billion year ago, it was a hellish world of molten lava. Earth eventually cooled enough for a crust to form and liquid oceans to appear. Soon after, as early as 4.1 billion years ago, life arose.

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At that time, the average temperature at the planet’s surface would have approached the boiling point of water — 100 degrees Celsius, about 75 degrees higher than today.

To explore how the heat would have affected early life forms, the researchers focused on a DNA mutation in which cytosine (one of the four nucleotide bases in the genetic code: “C”) turns into thymine (“T” in the genetic code). They experimentally tested the rates at which this mutation occurred spontaneously over a range of temperatures.

“Cytosine-based mutations, when the temperature was near 100 degrees Celsius, occurred at more than 4,000 times the modern rate,” study lead author Richard Wolfenden said in a news release. “To me, that was surprising. I thought the ancient rate would be more rapid than the modern rate, but not that rapid.”

With early life forms exposed to such staggering temperatures and constantly being hit with genetic mutations, it’s a wonder that they were able to survive. However, Wolfenden notes that even today there are microorganisms living in hot springs and deep-sea thermal vents that thrive at temperatures as high as 120 degrees Celsius.

Over time, as life forms evolved, they gained increasingly sophisticated means of fixing DNA damage.

“These findings give us some idea of the burden faced by primordial organisms before they evolved sophisticated systems for repair,” Wolfenden said. “And they offer another clue about how evolution kick-started the creation of the diverse world we see today.”

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