Isotope composition and volume of Earth’s early oceans
Open accessAbstract
Oxygen and hydrogen isotope compositions of Earth’s seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs, but hydrogen’s was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater. Archaean oceans were depleted in deuterium [expressed as δ D relative to Vienna standard mean ocean water (VSMOW)] by at most 25 ± 5‰, but oxygen isotope ratios were comparable to modern oceans. Mass balance of the global hydrogen budget constrains the contribution of continental growth and planetary hydrogen loss to the secular evolution of hydrogen isotope ratios in Earth’s oceans. Our calculations predict that the oceans of early Earth were up to 26% more voluminous, and atmospheric CH 4 and CO 2 concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on Archaean Earth.
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This lighter D/H could be explained by rapid Archean escape of hydrogen and isotopic fractionation.
“Third, the deuterium-to-hydrogen (D/H) ratio of 3.7 Ga-old seawater estimated from serpentine minerals is 2.5% lighter than today, which could be explained by rapid Archean escape of hydrogen and isotopic fractionation (185, 186).”
From The Archean atmosphere (2020) · cites this paper as [185]
The Conclusions report that early Archaean seawater was depleted in deuterium by about 25‰, and Models for a Global Hydrogen Budget considers hydrogen escape as one contributor to the subsequent isotopic shift. But the model does not characterize escape as rapid and explicitly says that no D/H fractionation occurs during diffusion-limited hydrogen escape; it identifies sequestration of low-deuterium water as the primary contributor. (LLM, conf=0.87)
Experimental — accuracy not yet measuredThe D/H ratio of 3.7 Ga-old seawater estimated from serpentine minerals is 2.5% lighter than today.
“Third, the deuterium-to-hydrogen (D/H) ratio of 3.7 Ga-old seawater estimated from serpentine minerals is 2.5% lighter than today, which could be explained by rapid Archean escape of hydrogen and isotopic fractionation (185, 186).”
From The Archean atmosphere (2020) · cites this paper as [185]
The Serpentines in the Isua Supracrustal Belt section derives a δD value of −25 ± 5‰ from serpentine-forming fluids, corresponding to a central estimate 2.5% below modern seawater. But the paper dates the material to about 3.8 Ga, not 3.7 Ga, and calls the value a minimum estimate rather than an unqualified seawater value. Page numbers are unavailable in our copy. (LLM, conf=0.87)
Experimental — accuracy not yet measuredTalc-carbonate veins crosscut oceanic antigorite, suggesting the veins postdate serpentinization and are related to mobilization of late-stage CO2-rich metamorphic fluids under retrograde conditions.
“The talc-carbonate veins crosscut oceanic antigorite (sample 15 -05 ; Pope et al., 2012), which suggests that the veins postdate serpentinization and are related to mobilization of a late-stage CO2-rich metamorphic fluids under retrograde conditions.”
From Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks (2016) · cites this paper as Pope et al., 2012
In “Serpentines in the Isua Supracrustal Belt” (page unavailable), the paper identifies sample 15-05 among samples used to assess antigorite formed in an oceanic setting. It does not report talc-carbonate veins crosscutting that sample, so it supports the sample identification but not the crosscutting observation to which the citation is attached. The subsequent interpretation of the veins is phrased as the citing authors’ inference. (LLM, conf=0.83)
Experimental — accuracy not yet measuredMeasurements find ancient δ18Oseawater ~0‰ in 2-Ga-old ophiolites, 3.8-Ga-old serpentine minerals, Archean pillow basalts, and kerogens in Archean cherts.
“However, measurements find ancient δ18Oseawater ~0‰ (Vienna standard mean ocean water) in 2-Ga-old ophiolites (232), 3.8-Ga-old serpentine minerals (185), Archean pillow basalts (233), and kerogens in Archean cherts (234).”
From The Archean atmosphere (2020) · cites this paper as [185]
Evidence points to high levels of Archean CH4.
“Evidence points to high levels of Archean CH4 (Fig. 3B).”
From The Archean atmosphere (2020) · cites this paper as [185]
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“…the lower luminosity of the young Sun and uncertainties about the abundance of greenhouse gases and continental area at the time, it is also possible that Earth cooled down relatively quickly to lower temperatures after its formation (Sleep et al., 2001; Rosing et al., 2010; Pope et al., 2012).”
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“This low D/H ratio of the Eoarchean ocean could be explained by the preferential loss of hydrogen from the deuterium-depleted early oceans to the mantle through subduction over geologic time, which suggests more voluminous oceans in the early Archean (Kurokawa et al., 2018; Pope et al., 2012).”
BackgroundWarm Archaean oceans reconstructed from oxygen isotope composition of early-life remnants
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Self-citationSubduction and atmospheric escape of Earth's seawater constrained by hydrogen isotopes
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“The D/H ratio of paleo-seawater has been estimated from isotopic analysis of minerals and rocks which interacted with seawater (Wenner and Taylor, 1974; Lécuyer et al., 1996; Kyser et al., 1999; Hren et al., 2009; Pope et al., 2012).”
BackgroundInfluentialSubaerial Emergence of Continents on Archean Earth
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- Authors
- Pope, E. C., Bird, D. K., & Rosing, M. T.
- Affiliations
- University of Copenhagen (DK)
- Venue
- Proceedings of the National Academy of Sciences
- Publisher
- National Academy of Sciences
- Published
- 2012-03-05
- Volume
- 109
- Issue
- 12
- Pages
- 4371-4376
- ISSN
- 0027-8424 (ISSN-L)
- 1091-6490
- PMC
- PMC3311330
- OpenAlex
- W2126643678
- Cited by
- 160
- References
- 59
- Citations by year
- 2026: 5 · 2025: 10 · 2024: 11 · 2023: 9 · 2022: 12 · 2021: 20 · 2020: 18 · 2019: 16 · 2018: 13 · 2017: 10 · 2016: 10 · 2015: 7 · 2014: 5 · 2013: 10 · 2012: 3
- FWCI
- 5.95
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Proceedings of the National Academy of Sciences (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- Research at the University of Copenhagen (University of Copenhagen) (submittedVersion)
- Funders
- National Research Foundation
- Danmarks Grundforskningsfond
- Topics
- Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Stratigraphy of Fossils
- Physical Sciences › Earth and Planetary Sciences › Geophysics › Geological and Geochemical Analysis
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astro and Planetary Science
- Keywords
- early Earth oceans, oxygen isotopes, hydrogen isotopes, deuterium depletion, serpentine, Isua supracrustal belt, crustal growth, atmospheric methane, atmospheric CO2, early Earth climate, volatile fluxes
- MeSH terms
- Geology, Hydrogen, Isotopes, Minerals, Oceans and Seas, Oxygen, Seawater, Earth, Planet, Geologic Sediments, Evolution, Planetary, Geological Phenomena
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