Theoretical origin of life; a combined RNA/DNA start (Introduction)

by David Turell , Monday, June 22, 2020, 22:47 (1615 days ago) @ David Turell

that's the new proposal as usdual based on lab based invented evidence:

https://www.scientificamerican.com/article/the-first-gene-on-earth-may-have-been-a-hybr...

"DNA and RNA, the two major modern forms of genetic code underpinning all of earthly biology, could have coexisted in strict pairings on our planet before life arose here, scientists in England, Scotland and Poland say. Using a hydrogen cyanide–based chemical system intended to mimic conditions in Earth’s early history, the researchers made four bases, the molecular “letters” of the genetic alphabet. Strung together, these bases form gene sequences that cells translate into proteins. But surprisingly, the team found that of the four bases their experiments consistently made, two were in a form found in DNA, whereas the other two were of a kind seen in RNA.

"The study, ... further undermines the so-called RNA world hypothesis. This idea, long one of the most prominent in origins-of-life research, posits that RNA formed the basis of Earth’s biosphere long before DNA and other molecules important to life emerged. Yet to date, scant evidence has been found of chemical pathways to make the RNA-exclusive system that rigid versions of the idea adopt or that could lead to DNA. “People have tended to think of RNA as the parent of DNA,” Sutherland says. “This [paper] suggests that they are molecular siblings.”

"Other scientists who were not involved with the study question the plausibility of the conditions used in this hydrogen cyanide-based route, however. Frances Westall, director of the exobiology group at the French National Center for Scientific Research’s Center for Molecular Biophysics in Orléans, notes that forming the bases requires very specific conditions. Mixtures would need to dry out and be exposed to ultraviolet light—two hurdles most easily surmounted on dry land, which was in short supply during our planet’s ocean-covered early days more than four billion years ago. “These conditions certainly existed on the early Earth,” Westall says. “They would not have been that common because there was not that much exposed landmass.” Although she adds that the study is “clever” and “not completely impossible,” she concludes that “there are other, better hypotheses as to locations for the emergence of life and prebiotic molecules.”

***

"This is a key issue for Nicholas Hud, an origins-of-life researcher at the Georgia Institute of Technology, who was not involved in the study. He calls it an “excellent compilation of organic chemistry research” on water-based nucleoside synthesis. But Hud is not convinced that the paper resolves whether these nucleosides actually arose before living creatures. His own research suggests amino acids could have linked up to carry information and act as a catalyst before RNA. Hud thinks evolution would then have gradually produced the current genetic system over long stretches of geologic time. “If a molecule looks very difficult, from a chemical perspective, to make, yet it functions exquisitely in biology, then it’s probably the case that it has been evolved over time,” he says. For the same reasons, he is also skeptical about the RNA world hypothesis.

"Furthermore, Hud sees the new study’s reliance on rigid incremental steps, each performed in strict order and under carefully controlled conditions, as a significant weakness. If the order of the steps changed or certain products were not isolated, Sutherland and his colleagues would have made much less of the substances they are interested in, Hud says. That caveat reduces the chances of the scenario unfolding in the chaotic environs of the early Earth."

comment: Just more fun and games with intelligent design in a lab and even the researchers very doubtful about each 'new' advance.