Cosmic Rays May Explain Life's Bias for Right-Handed DNA - Quanta Magazine

Lopsided interactions between cosmic-ray particles and chiral biomolecules may explain why all life on Earth relies exclusively on right-handed DNA and RNA helixes.

“This is one of the links between life on Earth and the cosmos,” wrote Louis Pasteur, one of the first scientists to recognize the asymmetry in life’s molecules, in 1860.

(Quanta Magazine is an editorially independent publication sponsored by the Simons Foundation, which also funds the Flatiron Institute.) But Globus didn’t think much about how cosmic rays might affect life until 2018 when she was a visiting scholar at the Kavli Institute for Particle Astrophysics and Cosmology, where she met Roger Blandford, a fellow astrophysicist and the Stanford University institute’s former director.

They started from the fact that cosmic ray showers, like DNA strands, have handedness.

Some had DNA or RNA strands that curled like ours, which she and Blandford dubbed “live” molecules (chiral naming conventions differ by field), and others had mirror-reversed strands — “evil” life.

With a series of toy models, the researchers calculated that the biased cosmic ray particles were ever-so-slightly more likely to knock an electron loose from a “live” helix than from an “evil” one, an event that theoretically causes mutations.

Over perhaps a million years, Globus suggests, cosmic rays might have accelerated the evolution of our earliest ancestors, letting them out-compete their “evil” rivals.

Proof that the handedness of particles really can mutate microbes would strengthen their case that cosmic rays shoved our ancestors off the evolutionary starting block, but it still wouldn’t fully explain the uniform chirality of life on Earth.

The simple amino acid molecules that form proteins also exist in “live” configurations favored by life and “evil” configurations that are not (although the preferred chirality for “live” amino acids is almost exclusively left-handed).

Careful analysis of meteorites by Dworkin and others has found that certain “live” amino acids outnumber “evil” ones by 20% or more, a surplus they may have passed on to Earth.

But, like the cosmic rays, the beams of light have a marginal effect.

On Earth, the doses of cosmic rays — which he likens to supersonic bullets — that would be needed to make a noticeable chiral difference might prove too lethal, he speculated