Theoretical origin of life: a new chemical approach (Introduction)

by David Turell , Monday, April 09, 2018, 20:09 (2420 days ago) @ David Turell

Using volcanic products that had to be present on Earth:

https://www.sciencedaily.com/releases/2018/04/180409103833.htm

"Around 4 billion years ago, Earth was an inhospitable place, devoid of oxygen, bursting with volcanic eruptions, and bombarded by asteroids, with no signs of life in even the simplest forms. But somewhere amid this chaotic period, the chemistry of the Earth turned in life's favor, giving rise, however improbably, to the planet's very first organisms.

"The researchers found that a class of molecules called sulfidic anions may have been abundant in Earth's lakes and rivers. They calculate that, around 3.9 billion years ago, erupting volcanoes emitted huge quantities of sulfur dioxide into the atmosphere, which eventually settled and dissolved in water as sulfidic anions -- specifically, sulfites and bisulfites. These molecules likely had a chance to accumulate in shallow waters such as lakes and rivers.

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"Preliminary work by Ranjan and his collaborators suggest that sulfidic anions would have sped up the chemical reactions required to convert very simple prebiotic molecules into RNA, a genetic building block of life.

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"In 2015, chemists from Cambridge University, led by John Sutherland, who is a co-author on the current study, discovered a way to synthesize the precursors to RNA using just hydrogen cyanide, hydrogen sulfide, and ultraviolet light -- all ingredients that are thought to have been available on early Earth, before the appearance of the first life forms.

"From a chemistry point of view, the researchers' case was convincing: The chemical reactions they carried out in the laboratory overcame longstanding chemical challenges, to successfully yield the genetic building blocks to life. But from a planetary science standpoint, it was unclear whether such ingredients would have been sufficiently abundant to jumpstart the first living organisms.

"For instance, comets may have had to rain down continuously to bring enough hydrogen cyanide to Earth's surface. Meanwhile, hydrogen sulfide, which would have been released in huge amounts by volcanic eruptions, would have mostly stayed in the atmosphere, as the molecule is relatively insoluble in water, and therefore would not have had regular opportunities to interact with hydrogen cyanide.

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"They took away from that [talk] that, on early Earth, you don't have much oxygen, but you do have sulfur dioxide from volcanism," Ranjan recalls. "As a consequence, you should have sulfites. And they said, 'Can you tell us how much of this molecule there would have been?' And that's what we set out to constrain."

"To do so, he started with a volcanism model developed previously by Sara Seager, MIT's Class of 1941 Professor of Planetary Sciences, and her former graduate student Renyu Hu.

"'They did a study where they asked, 'Suppose you take the Earth and just crank up the amount of volcanism on it. What concentrations of gases do you get in the atmosphere?'" Ranjan says.

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"Ultimately, he found that, while volcanic eruptions would have spewed huge quantities of both sulfur dioxide and hydrogen sulfide into the atmosphere, it was the former that dissolved more easily in shallow waters, producing large concentrations of sulfidic anions, in the form of sulfites and bisulfites.

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"Early experiments led by Ranjan's colleagues suggest that sulfites and bisulfites may have indeed encouraged biomolecules to form. The team carried out chemical reactions to synthesize ribonucleotides with sulfites and bisulfites, versus with hydrosulfide, and found the former were able to produce ribonucleotides and related molecules 10 times faster than the latter, and at higher yields. More work is needed to confirm whether sulfidic anions were indeed early ingredients in brewing up the first life forms, but there is now little doubt that these molecules were part of the prebiotic milieu."

Comment: hope springs eternal. Design work in the lab isn't uncontrolled experiments like this. Life's appearance is miraculous. RNA is a specific type of molecule out of many possible molecular forms appearing by chance. The start of life requires design.