Serpentinite and the dawn of life

Our plain-English summary of Serpentinite and the dawn of life, by N.H. Sleep, D.K. Bird, E.C. Pope (Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 2011).

The study

• Authors: N.H. Sleep, D.K. Bird, E.C. Pope
• Journal: Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
• Published: 2011;366(1580):2857-69
• Cited by: 86 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Submarine hydrothermal vents above serpentinite produce chemical potential gradients of aqueous and ionic hydrogen, thus providing a very attractive venue for the origin of life. This environment was most favourable before Earth's massive CO(2) atmosphere was subducted into the mantle, which occurred tens to approximately 100 Myr after the moon-forming impact; thermophile to clement conditions persisted for several million years while atmospheric pCO(2) dropped from approximately 25 bar to below 1 bar. The ocean was weakly acid (pH ∼ 6), and a large pH gradient existed for nascent life with pH 9-11 fluids venting from serpentinite on the seafloor. Total CO(2) in water was significant so the vent environment was not carbon limited. Biologically important phosphate and Fe(II) were somewhat soluble during this period, which occurred well before the earliest record of preserved surface rocks approximately 3.8 billion years ago (Ga) when photosynthetic life teemed on the Earth and the oceanic pH was the modern value of approximately 8. Serpentinite existed by 3.9 Ga, but older rocks that might retain evidence of its presence have not been found. Earth's sequesters extensive evidence of Archaean and younger subducted biological material, but has yet to be exploited for the Hadean record.

In plain English

This article is not a study of asbestos exposure or human health. It is a geology paper written for a meeting on the chemical origins of life. It drew on earlier work to examine whether hot springs on the seafloor above serpentinite could have been where life began. Serpentinite is a rock made mostly of serpentine minerals. The authors reasoned that the conditions this vent hypothesis needs, a weakly acid ocean under a carbon dioxide-rich atmosphere, were short-lived in early Earth history. They gave a tentative estimate of 2.5 to 25 million years for removing the last approximately 25 bars of atmospheric carbon dioxide. They described evidence for serpentinite at Earth's surface by about 3.9 billion years ago and for abundant life by about 3.8 billion years ago. For that hypothesis, the authors concluded, their reasoning left a narrow window of several million years for life's origin, while the last of Earth's massive carbon dioxide atmosphere was subducted into the mantle. They noted that the timing is poorly constrained and that rocks showing serpentinite at the dawn of life have not been found.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Review and theoretical discussion paper (geology and geochemistry), one contribution to a discussion meeting issue on the origins of life; not an epidemiological, clinical or animal study
• Who was studied: No people or animals. The paper considered the early Earth (the Hadean and early Archaean) and the geological and geochemical record bearing on hydrothermal vents above serpentinite
• Exposure: No health exposure was studied. The subject is serpentinite rock, whose dominant minerals are serpentine, brucite and magnetite, as a possible setting for the origin of life
• Main results:
  • The authors described the most favourable pre-biotic environment, with high atmospheric carbon dioxide and seawater of about pH 6 above ocean-floor serpentinite, as transient and lasting only several million years
  • A tentative estimate put the time needed to remove the last approximately 25 bars of atmospheric carbon dioxide at 2.5 to 25 million years
  • At 3 bar of carbon dioxide, the early ocean pH was approximately 5.8 and total dissolved carbon dioxide was over an order of magnitude above present levels
  • Under these conditions carbon was not limiting, and iron(II) and phosphorus were reasonably soluble
  • The authors saw evidence for serpentinite back to approximately 3.9 billion years ago
  • Geological observations suggest the Earth teemed with life by approximately 3.8 billion years ago
• The authors' conclusion: The authors concluded that, for the vent hypothesis they examined (a pH gradient between alkaline vent fluid and an ocean of about pH 6), their reasoning gives a narrow window of several million years for the origin of life, while the last of Earth's massive carbon dioxide atmosphere was subducted into the mantle. They also concluded that evidence of life from before about 4 billion years ago may be preserved only in Earth's mantle
• Limitations the authors state:
  • The timing and duration of the loss of the massive carbon dioxide atmosphere are poorly constrained
  • There is no direct evidence of serpentinite at the dawn of life because rocks that might record it have not been found
  • There is no geological evidence of ocean pH from before photosynthesis arose
  • Very little is known geologically about the timing or duration of the 'RNA world'

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Serpentinite, Venue.

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• Sources of organic nitrogen at the serpentinite-hosted Lost City hydrothermal field — S.Q. Lang, G.L. Früh-Green, et al. (2013)
• The Lost City Hydrothermal Field: A Spectroscopic and Astrobiological Analogue for Nili Fossae, Mars — E.S. Amador, J.L. Bandfield, et al. (2017)
• Occurrence of heavy metal-resistance in microflora from serpentine soil of Andaman — A. Pal, S. Dutta, et al. (2005)
• Comparison of 16S rRNA and 16S rDNA T-RFLP approaches to study bacterial communities in soil microcosms treated with chromate as perturbing agent — A. Mengoni, E. Tatti, et al. (2005)

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