It Came from Outer Space –“The Spark for the Molecular Evolution of Life as We Know It?” 

 

Comet 67P/Churyumov-Gerasimenko, ESA/Rosetta/NAVCAM

 

Phosphates, a key building block for life, was found to be generated in outer space and delivered to early Earth by meteorites or comets. All living beings need cells and energy to replicate. Without these fundamental building blocks, living organisms on Earth would not be able to reproduce and would simply not exist.

“On Earth, phosphine (PH3) is lethal to living beings,” said University of Hawaii researchers in their study, Did key building blocks for life come from deep space?. “But in the interstellar medium, an exotic phosphine chemistry can promote rare chemical reaction pathways to initiate the formation of biorelevant molecules such as oxoacids of phosphorus, which eventually might spark the molecular evolution of life as we know it.”

Venus: Secrets of Our Strange Sister Planet

Key Element in the Building Blocks of Life

Little was known about a key element in the building blocks, phosphates, until now. University of Hawaii at Manoa researchers, in collaboration with colleagues in France and Taiwan, provide compelling new evidence that this component for life was found to be generated in outer space and delivered to Earth in its first one billion years by meteorites or comets. The phosphorus compounds were then incorporated in biomolecules found in cells in living beings on Earth.

Phosphine on Venus: A Red Herring?

A September 2020 report that there may be phosphine gas in the Venusian clouds came with a stunning implication: extraterrestrial life. On Earth, phosphine is a chemical produced by some kinds of bacteria that live in oxygen-poor conditions. Its presence on Venus, announced by a team led by Cardiff University’s Jane Greaves, raised the possibility that there could be life in what has long been thought one of the most inhospitable environments in the solar system: a planet that’s covered in thick clouds of sulfuric acid, with an atmosphere that’s 96% carbon dioxide, and where the pressure at the surface is 100 times greater than Earth’s. Oh, and it experiences temperatures up to 471 °C—well above the melting point of lead.

Since the initial report, though, doubt about the finding has crept in. Three different preprint papers (none of which have been published in a peer-reviewed journal, although one has been accepted) were unable to find the same evidence of phosphine on Venus.

“Instead of phosphine in the clouds of Venus, the data are consistent with an alternative hypothesis: They were detecting sulfur dioxide,” said co-author Victoria Meadows, a University of Washington professor of astronomy. “Sulfur dioxide is the third-most-common chemical compound in Venus’ atmosphere, and it is not considered a sign of life.”

The breakthrough research is outlined in “An Interstellar Synthesis of Phosphorus Oxoacids,” authored by University of Hawaii Manoa graduate student Andrew Turner, now assistant professor at the University of Pikeville, and University of Hawaii Manoa chemistry Professor Ralf Kaiser in the September issue of Nature Communications.

According to the study, phosphates and diphosphoric acid are two major elements that are essential for these building blocks in molecular biology. They are the main constituents of chromosomes, the carriers of genetic information in which DNA is found. Together with phospholipids in cell membranes and adenosine triphosphate, which function as energy carriers in cells, they form self-replicating material present in all living organisms.

In an ultra-high vacuum chamber cooled down to 5 K (-450°F) in the W.M. Keck Research Laboratory in Astrochemistry at UH Manoa, the Hawaii team replicated interstellar icy grains coated with carbon dioxide and water, which are ubiquitous in cold molecular clouds, and phosphine. When exposed to ionizing radiation in the form of high-energy electrons to simulate the cosmic rays in space, multiple phosphorus oxoacids like phosphoric acid and diphosphoric acid were synthesized via non-equilibrium reactions.

Kaiser added, “The phosphorus oxoacids detected in our experiments by combination of sophisticated analytics involving lasers, coupled to mass spectrometers along with gas chromatographs, might have also been formed within the ices of comets such as 67P/Churyumov-Gerasimenko, which contains a phosphorus source believed to derive from phosphine.” Kaiser says these techniques can also be used to detect trace amounts of explosives and drugs.

“Since comets contain at least partially the remnants of the material of the protoplanetary disk that formed our solar system, these compounds might be traced back to the interstellar medium wherever sufficient phosphine in interstellar ices is available,” said Cornelia Meinert of the University of Nice (France).

Upon delivery to Earth by meteorites or comets, these phosphorus oxoacids might have been available for Earth’s prebiotic phosphorus chemistry. Hence an understanding of the facile synthesis of these oxoacids is essential to untangle the origin of water-soluble prebiotic phosphorus compounds and how they might have been incorporated into organisms not only on Earth, but potentially in our universe as well.

The Last Word–Indicator of Extraterrestrial life or Science Fiction?

“We have scientific evidence that PH3 can act under the right conditions on interstellar grains as a precursor to phosphorus oxoacids and also to alkyl phosphonic acids,” wrote Ralf I. Kaiser, Professor and Director of the W.M. Keck Research Laboratory in Astrochemistry in an email to The Daily Galaxy.  “It can even lead – once again under the right conditions – to glycerolphosphates on interstellar grains as established in our lab. That’s it. 

“Speculations that the presence of PH3 is an indicator of extraterrestrial life,” concludes Kaiser in his email, “has no foundation. These speculations do not help much to mature the field of astrochemistry but should be discussed in the context of science fiction.”

Image credit top of page: Comet 67P/Churyumov-Gerasimenko,  ESA/Rosetta/NAVCAM

Ralf I. Kaiser, University of Hawaii and Nature

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