Why didn’t gamma radiation prevent life on Earth from starting?

Biophysicists might be able to answer the question of why the chemical building blocks which formed the first life on earth were able to survive despite being bathed in gamma radiation.

Earth formed about 4.5 billion years ago. It’s estimated that the first life on our planet – single-celled organisms – emerged out of the “primordial soup” of chemicals in the first oceans 4 billion years ago. But it’s not clear why radiation didn’t prevent these chemicals from forming life in the first place.

Today, Earth is protected from harmful cosmic radiation by our magnetic field. Scientists aren’t clear on the exact age, but it’s estimated that the magnetic field only formed, at most, about 3.5 billion years ago.

Such radiation causes the production of reactive forms of oxygen that damage organic molecules.

New research published in Nature Communications suggests that the first cell-like structures on Earth contained radiation-resistant manganese antioxidants, protecting the first cells to evolve.

Previous studies have shown that chains of phosphate residues and manganese ions protect organic molecules from oxidative stress caused by radiation. This has been seen in the bacterium Deinococcus radiodurans, which is resistant to high doses of gamma radiation.

Two models of the first cells, called protocells, are proposed in the new research. These “coacervates” (liquid droplets that model protocells) are polyphosphate-manganese and polyphosphate-peptide coacervates.

Exposure to high levels of gamma radiation saw the polyphosphate-manganese coacervates stay intact while the polyphosphate-peptide coacervates were destroyed.

The authors, led by biophysicist Professor Bing Tian from the Zheijiang University in China, believe that this could give an insight into how protocells formed and were able to survive high radiation on early Earth.

They suggest that a polyphosphate-manganese coacervate might have provided protection for proteins and the first DNA molecules that were absorbed into the first protocells.

These protocells would over a billion years evolve into the first cyanobacteria and eventually eukaryotic cells which would evolve into the first animals.

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