期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2021
卷号：118
期号：23
页码：1
DOI：10.1073/pnas.2023617118
出版社：The National Academy of Sciences of the United States of America
摘要：The low 18 O/ 16 O stable isotope ratios (δ 18 O) of ancient chemical sediments imply ∼70 °C Archean oceans if the oxygen isotopic composition of seawater (sw) was similar to modern values. Models suggesting lower δ 18 O sw of Archean seawater due to intense continental weathering and/or low degrees of hydrothermal alteration are inconsistent with the triple oxygen isotope composition (Δ’ 17 O) of Precambrian cherts. We show that high CO 2 sequestration fluxes into the oceanic crust, associated with extensive silicification, lowered the δ 18 O sw of seawater on the early Earth without affecting the Δ’ 17 O. Hence, the controversial long-term trend of increasing δ 18 O in chemical sediments over Earth’s history partly reflects increasing δ 18 O sw due to decreasing atmospheric p CO 2 . We suggest that δ 18 O sw increased from about −5‰ at 3.2 Ga to a new steady-state value close to −2‰ at 2.6 Ga, coinciding with a profound drop in p CO 2 that has been suggested for this time interval. Using the moderately low δ 18 O sw values, a warm but not hot climate can be inferred from the δ 18 O 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- p CO 2 greenhouse atmosphere before 3 Ga.
关键词：triple oxygen isotopes ; Archean ; climate ; faint young Sun ; plate tectonics
