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Origin of Life’s Handedness

Cosmic Rays May Have Played Key Role in Origin of Life’s Handedness

Living organisms comprise a system of molecules organized with specific handedness. Handedness — or chirality — is the geometric property of an object that cannot be superimposed on its mirror image. In a paper published in the Astrophysical Journal Letters, a duo of researchers speculates that the interaction between proto-lifeforms and magnetically polarized cosmic rays may be responsible for this structural preference in biological molecules.

Cosmic rays. Image credit: Pierre Auger Observatory.

Cosmic rays. Image credit: Pierre Auger Observatory.

Biological homochirality was discovered in 1848 by the French biologist, microbiologist and chemist Louis Pasteur.

Since then, scientists have debated whether the handedness of life was driven by random chance or some unknown deterministic influence.

Pasteur hypothesized that, if life is asymmetric, then it may be due to an asymmetry in the fundamental interactions of physics that exist throughout the cosmos.

“We propose that the biological handedness we witness now on Earth is due to evolution amidst magnetically polarized radiation, where a tiny difference in the mutation rate may have promoted the evolution of DNA-based life, rather than its mirror image,” said Dr. Noémie Globus, a researcher in the Center for Cosmology Particle Physics at New York University and the Center for Computational Astrophysics at Flatiron Institute.

In their paper, Dr. Globus and Stanford University’s Professor Roger Blandford argue that cosmic rays are an important piece of the chiral puzzle of life.

“Cosmic rays are an abundant form of high-energy radiation that originate from various sources throughout the Universe, including stars and distant galaxies,” they explained.

“After hitting the Earth’s atmosphere, cosmic rays eventually degrade into fundamental particles. At ground level, most of the cosmic rays exist only as particles known as muons.”

“Muons are unstable particles, existing for a mere 2 millionths of a second, and are magnetically polarized, meaning, on average, muons all share the same magnetic orientation. When muons finally decay, they produce electrons with the same magnetic polarization.”

Showers of high-energy particles originating from the Sun and our Milky Way Galaxy collide with nitrogen and oxygen in the upper atmosphere. At ground level, the shower is dominated by magnetically polarized muons. At the protobiological site, nucleic acids assumed either a right-handed or left-handed helical conformation. The magnetically polarized radiation preferentially ionized one type of handedness leading to a slightly different mutation rate between the two mirror proto-lifeforms. Over time, right-handed molecules out-evolved their left-handed counterparts. Image credit: Simons Foundation.

Showers of high-energy particles originating from the Sun and our Milky Way Galaxy collide with nitrogen and oxygen in the upper atmosphere. At ground level, the shower is dominated by magnetically polarized muons. At the protobiological site, nucleic acids assumed either a right-handed or left-handed helical conformation. The magnetically polarized radiation preferentially ionized one type of handedness leading to a slightly different mutation rate between the two mirror proto-lifeforms. Over time, right-handed molecules out-evolved their left-handed counterparts. Image credit: Simons Foundation.

The scientists believe that the muon’s penetrative ability allows it and its daughter electrons to potentially affect chiral molecules on Earth and everywhere else in the Universe.

Their hypothesis is that, at the beginning of life of on Earth, this constant and consistent radiation affected the evolution of the two mirror life-forms in different ways, helping one ultimately prevail over the other.

These tiny differences in mutation rate would have been most significant when life was beginning and the molecules involved were very simple and more fragile.

Under these circumstances, the small but persistent chiral influence from cosmic rays could have, over billions of generations of evolution, produced the single biological handedness we see today.

The researchers suggest experiments that could help prove or disprove their cosmic ray hypothesis. For example, they would like to test how bacteria respond to radiation with different magnetic polarization.

“Experiments like this have never been performed and I am excited to see what they teach us. Surprises inevitably come from further work on interdisciplinary topics,” Dr. Globus said.

The team also looks forward to organic samples from comets, asteroids or Mars to see if they too exhibit a chiral bias.

“This idea connects fundamental physics and the origin of life,” Professor Blandford said.

“Regardless of whether or not it’s correct, bridging these very different fields is exciting and a successful experiment should be interesting.”

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Noemie Globus Roger D. Blandford. 2020. The Chiral Puzzle of Life. ApJL 895, L11; doi: 10.3847/2041-8213/ab8dc6

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