In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 118, No. 33 ( 2021-08-17)
Kurzfassung:
Earth’s early atmosphere witnessed multiple transient episodes of oxygenation before the Great Oxidation Event 2.4 billion years ago (Ga) [e.g., A. D. Anbar et al., Science 317, 1903–1906 (2007); M. C. Koehler, R. Buick, M. E. Barley, Precambrian Res. 320, 281–290 (2019)], but the triggers for these short-lived events are so far unknown. Here, we use mercury (Hg) abundance and stable isotope composition to investigate atmospheric evolution and its driving mechanisms across the well-studied “whiff” of O 2 recorded in the ∼2.5-Ga Mt. McRae Shale from the Pilbara Craton in Western Australia [A. D. Anbar et al., Science 317, 1903–1906 (2007)]. Our data from the oxygenated interval show strong Hg enrichment paired with slightly negative ∆ 199 Hg and near-zero ∆ 200 Hg, suggestive of increased oxidative weathering. In contrast, slightly older beds, which were evidently deposited under an anoxic atmosphere in ferruginous waters [C. T. Reinhard, R. Raiswell, C. Scott, A. D. Anbar, T. W. Lyons, Science 326, 713–716 (2009)] , show Hg enrichment coupled with positive ∆ 199 Hg and slightly negative ∆ 200 Hg values. This pattern is consistent with photochemical reactions associated with subaerial volcanism under intense UV radiation. Our results therefore suggest that the whiff of O 2 was preceded by subaerial volcanism. The transient interval of O 2 accumulation may thus have been triggered by diminished volcanic O 2 sinks, followed by enhanced nutrient supply to the ocean from weathering of volcanic rocks causing increased biological productivity.
Materialart:
Online-Ressource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.2107511118
Sprache:
Englisch
Verlag:
Proceedings of the National Academy of Sciences
Publikationsdatum:
2021
ZDB Id:
209104-5
ZDB Id:
1461794-8
SSG:
11
SSG:
12
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