Theoretical origin of life; importance of chirality (Introduction)

by David Turell @, Monday, June 29, 2020, 19:33 (5 days ago) @ David Turell

Chirality is a knife in the heart of theoretical natural chance origin of life theories. This is an attempt to explain it:

"Cosmic Rays May Explain Life’s Bias for Right-Handed DNA


"The theory, which appeared in May in The Astrophysical Journal Letters, doesn’t explain every step of how life acquired its current handedness, but it does assert that the shape of terrestrial DNA and RNA is no accident. Our spirals might all trace back to an unexpected influence from cosmic rays.


"Physical events typically break right as often as they break left, but cosmic ray particles called pions tap into one of nature’s rare exceptions. When pions decay, the process is governed by the weak force — the only fundamental force with a known mirror asymmetry. Pions slamming into the atmosphere produce showers of particles including electrons and their heavier siblings, muons, all of which are equipped by the weak force with the same chiral magnetic orientation relative to their path. The particles bounce around as they streak through the atmosphere, Globus said, but overall they tend to keep their preferred chirality when they slam into the ground.


"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.

"The effect would be tiny: Millions if not billions of cosmic ray strikes could be required to yield one additional free electron in a “live” strand, depending on the event’s energy. But if those electrons changed letters in the organisms’ genetic codes, those tweaks may have added up. 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. “If you don’t have mutations, you don’t evolve,” she said.


"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 theory doesn’t address, for example, how “live” organisms and “evil” organisms managed to materialize from a primordial smoothie containing both right- and left-handed building blocks.


"...another unknown process seems to handicap “evil” life. 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. The excess molecules could be the lucky survivors of billions of years of exposure to circularly polarized light, a collection of beams all spiraling in the same direction that, experiments have shown, can destroy one type of amino acid slightly more thoroughly than the other.

"But, like the cosmic rays, the beams of light have a marginal effect. Countless interactions would be needed to leave behind a noticeable imbalance, so some other force may be at work as well. Light would have to pulverize untenably huge quantities of molecules to explain the excesses on its own, Dworkin says.

"Sasselov has encouraged Globus and Blandford to consider whether cosmic rays might join forces with polarized light to shape the amino acids on asteroids. 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. “You’re destroying so much of everything,” he said. “You may be left with the [correct] handedness, but essentially you’re shooting yourself in the foot.” (m y bold)


“'There is something special about planets like the Earth that protect this kind of chemistry,” Sasselov said." (my bold)

Comment: It all appears to be against the odds. I like it. Each desperate experiment helps prove the need for a designer. The Earth is very special.

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