Freeze-thaw cycles on Earth triggered life, new study claims

AFP Photo/Mauricio Lima
British scientists have discovered that a series of rapid frosts and thaws could have been a “vital spark” for life to originate on Earth. They now believe that living cells naturally evolved from a biochemical soup at the early days of our planet.

A group of researchers from the Medical Research Council’s Laboratory of Molecular Biology in Cambridge found out that simple forms of DNA assemble themselves from small biochemical building blocks when repeatedly frozen and thawed, Chemistry World reports.

The latest study shows that, under certain conditions, short fragments of RNA - a type of single-strand DNA - can form long chains similar to enzymes that, according to many scientists’ beliefs, could have triggered the first biochemical reactions eventually leading to the emergence of living cells.

For the study, the research team took a long and complex RNA chain able of replicating genetic material and broke it into very small pieces consisting of several RNA building blocks called nucleotides.

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After subjecting these small RNA fragments to series of freezing and thawing cycles (from -9°C to +37°C), the researchers discovered that these pieces spontaneously reassembled themselves into large complex structures – an RNA molecule in its active state allowing it to replicate itself.

“It was surprising to see that small RNA pieces together with repeated freeze-thaw cycling would result in such efficient assembly of large RNAs,” Hannes Mutschler, the lead author of the research, told Chemistry World.

Taking into account the temperature gradients needed for the formation of RNA chains, Hannes Mutschler claimed that natural environment on the early Earth about 4 billion years ago could have provided all the necessary conditions for an RNA chain to form.

At that time Earth was a place with intensive hydrothermal activity and a heavy bombardment of meteorites, while temperatures on the planet’s surface would have varied wildly even between night and day, Chemistry World explains.

“Repeated freeze thaw cycles, likely to have occurred on the early earth diurnally, seasonally or as a result of periodic geothermal and meteoritic activity, emerge here as critical drivers of RNA assembly reactions,” Hannes Mutschler said.

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The new findings also lend support to the 'RNA world' hypothesis, according to which short molecular sequences of RNA precursors were initially formed via prebiotic chemistry before gaining the ability to carry and replicate genetic information, Chemistry World says.

However the processes, which were giving short molecular sequences of RNA precursors enough catalytic power to assemble highly complex RNA structures, remained unknown to the scientists.

All previous reports suggested that complex RNA structures capable of replicating themselves could be formed only by very long RNA chains, which are highly unlikely to be created under prebiotic conditions.

The recent study breathes a new life into this theory.

“To the best of our knowledge this is the first time that complex ribozymes (long RNA chains) have been assembled from RNA pieces short enough to be prebiotically plausible,” Mutschler said.

“Our work indicates that very primitive assemblers might have been present in the original pool of short RNAs created by prebiotic chemistry and could bootstrap themselves towards more complex catalytic functions by the formation of assembly networks.”

UK researches published the results of their study in the journal Nature Chemistry and it is already being hailed as a breakthrough in understanding a key step for the evolution of life.