Theoretical origin of life: needed chemicals rare (Introduction)

by David Turell , Saturday, September 03, 2022, 19:53 (812 days ago) @ David Turell

What is found in our universe is extremely low levels of possible precursors:

https://reasons.org/explore/blogs/todays-new-reason-to-believe/have-astronomers-found-l...

"For at least five decades, proponents of a naturalistic origin of life have been searching for evidence of the RNA world hypothesis. The RNA world is a proposed step in the evolution of life on Earth in which self-replicating RNA molecules preceded genetic material and proteins. Life on Earth appeared suddenly about 3.8 billion years ago. However, evidence for organic molecules that could possibly give rise to RNA is lacking on Earth; thus, astrobiologists believe the building blocks of life must reside in interstellar space.

***

"One of chemistry’s great enigmas is that nitriles are key precursor molecules of the nucleobases, which when joined to a ribose and a phosphate molecule comprise the fundamental building blocks of RNA and DNA molecules. RNA molecules together with DNA molecules, proteins, and lipids are the molecules every organism possesses and without which no life-form can possibly survive.

***

"Rivilla’s team detected the following four nitriles: cyanic acid, cyanoallene, propargyl cyanide, and cyanopropyne. They achieved tentative detections of cyanoformaldehyde and glycolonitrile. They did not detect cyanoacetaldehyde. Cyanoallene and propargyl cyanide had been previously detected in the TMC-1 dark molecular cloud, which, at a distance of only 140 light-years is the nearest large molecular interstellar cloud. The simplest oxygen-bearing nitrile, cyanic acid, was also previously detected in another giant molecular cloud at the galactic center.

"The measured abundance levels for the detected nitriles were very low. Even the simplest one, cyanic acid (HOCN), measured rare. Rivilla’s team determined that in G+0.693-0.027 there is only one molecule of cyanic acid for every 6 billion molecules of molecular hydrogen (H2). The three non-oxygen-bearing nitriles detected by Rivilla and his colleagues were measured, in each case, at one molecule for every 6–10 billion H2 molecules.

"The British newspaper, The Telegraph, in the headline of their report on the Rivilla team’s discoveries stated that the “building blocks of life” found by the team “suggests we are not alone.” One of Rivilla’s coauthors, Miguel Requena-Torres, was quoted as saying to Sarah Knapton, science editor for The Telegraph, “We now know that nitriles are among the most abundant chemical families in the universe.” By “chemical families,” Requena-Torres had to be referring to precursor molecules for nucleobases and amino acids. Another coauthor, Izaskun Jiménez-Serra, referring to such precursor molecules, said “There are still key missing molecules.”

"In the conclusion to their paper, Rivilla’s team noted that nitriles are not a direct precursor to either nucleobases or amino acids. The early Earth’s atmosphere would need to have been chemically reducing and must have contained high amounts of ammonia for amidines to possibly form from nitriles. Several amidines are direct precursors for nucleobases and amino acids. However, as we explained and documented in our book Origins of Life, Earth’s early atmosphere was neither reducing nor did it contain more than a trace amount of ammonia.

"What Ravilla’s team found were a few of the hundred-plus molecules that are the “building blocks of the building blocks of the building blocks” of life molecules. They found them at abundance levels far below what is needed for any conceivable naturalistic model for life’s origin. And they found them in an interstellar molecular cloud where the chemical reactions that produce them are counterbalanced by chemical reactions that destroy them.

"Thus, Ravilla’s team’s detections do not, as they claim, provide support for the RNA world hypothesis for the origin of life. Rather, their detections provide additional confirmation for what Fazale Rana and I heard Leslie Orgel, the father of the RNA world hypothesis, say in the opening plenary session message at the 2002 International Society for the Study of the Origin of Life conference, “It would be a miracle if a strand of RNA ever appeared on the primitive Earth.” (my bold)

Comment: the usual hype that solving the origin of life is right around the corner is dismissed by Hugh Ross. We should all listen to Leslie Orgel.