Universität zu Köln

Herwartz, Daniel ORCID: 0000-0003-3604-8295, Pack, Andreas ORCID: 0000-0002-2618-2768 and Nagel, Thorsten J. (2021). A CO2 greenhouse efficiently warmed the early Earth and decreased seawater O-18/O-16 before the onset of plate tectonics. Proc. Natl. Acad. Sci. U. S. A., 118 (23). WASHINGTON: NATL ACAD SCIENCES. ISSN 0027-8424

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Abstract

The low O-18/O-16 stable isotope ratios (delta O-18) of ancient chemical sediments imply similar to 70 degrees C Archean oceans if the oxygen isotopic composition of seawater (sw) was similar to modern values. Models suggesting lower delta O-18(sw) of Archean seawater due to intense continental weathering and/or low degrees of hydrothermal alteration are inconsistent with the triple oxygen isotope composition (Delta'O-17) of Precambrian cherts. We show that high CO2 sequestration fluxes into the oceanic crust, associated with extensive silicification, lowered the delta O-18(sw) of seawater on the early Earth without affecting the Delta'O-17. Hence, the controversial long-term trend of increasing delta O-18 in chemical sediments over Earth's history partly reflects increasing delta O-18(sw) due to decreasing atmospheric pCO(2). We suggest that delta O-18(sw) increased from about -5 parts per thousand at 3.2 Ga to a new steady-state value close to -2 parts per thousand at 2.6 Ga, coinciding with a profound drop in pCO(2) that has been suggested for this time interval. Using the moderately low delta O-18(sw) values, a warm but not hot climate can be inferred from the delta O-18 of the most pristine chemical sediments. Our results are most consistent with a model in which the faint young Sun was efficiently counterbalanced by a high-pCO(2) greenhouse atmosphere before 3 Ga.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Herwartz, Daniel UNSPECIFIED orcid.org/0000-0003-3604-8295 UNSPECIFIED Pack, Andreas UNSPECIFIED orcid.org/0000-0002-2618-2768 UNSPECIFIED Nagel, Thorsten J. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-581361
DOI:	10.1073/pnas.2023617118
Journal or Publication Title:	Proc. Natl. Acad. Sci. U. S. A.
Volume:	118
Number:	23
Date:	2021
Publisher:	NATL ACAD SCIENCES
Place of Publication:	WASHINGTON
ISSN:	0027-8424
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language OXYGEN ISOTOPIC COMPOSITION; BARBERTON GREENSTONE-BELT; TRIPLE OXYGEN; OCEANIC-CRUST; HYDROTHERMAL SYSTEMS; CONTINENTAL-CRUST; PILBARA CRATON; CARBON-DIOXIDE; EVOLUTION; CONSTRAINTS Multiple languages Multidisciplinary Sciences Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/58136