Chromium evidence for protracted oxygenation during the Paleoproterozoic

• Published in: Earth and planetary science letters 2022-04, Vol.584, p.117501, Article 117501
• Main Authors: Mänd, Kaarel, Planavsky, Noah J., Porter, Susannah M., Robbins, Leslie J., Wang, Changle, Kreitsmann, Timmu, Paiste, Kärt, Paiste, Päärn, Romashkin, Alexander E., Deines, Yulia E., Kirsimäe, Kalle, Lepland, Aivo, Konhauser, Kurt O.
• Format: Article
• Language: English
• Subjects: Cr isotopes; eukaryotes; isotope geochemistry; oxygen overshoot
• ISSN: 0012-821X; 1385-013X; 1385-013X
• DOI: 10.1016/j.epsl.2022.117501

It has commonly been proposed that the development of complex life is tied to increases in atmospheric oxygenation. However, there is a conspicuous gap in time between the oxygenation of the atmosphere 2.4 billion years ago (Ga) and the first widely-accepted fossil evidence for complex eukaryotic cells 2400-m core from the Onega Basin (NW-Russia), deposited ∼2.1–2.0 billion years ago—a few hundred million years prior to the oldest definitive fossil evidence for eukaryotes. Fractionated chromium isotopes are documented throughout the section (max. 1.63±0.10‰δ53Cr), suggesting a long interval (possibly >100 million years) during which oxygen levels were higher and more stable than in the billion years before or after. This suggests that, if it is the case that complex cells did not evolve until after 1.7 Ga, then this delay was not due to O2-limitation. Instead, it could reflect other limiting factors—ecological or environmental—or could indicate that it simply takes a long time—more than the tens to >100 million years recorded in Onega Basin sediments—for such biological innovations to evolve. •Two-billion-year-old Onega Basin rocks record pervasive Cr isotope fractionation.•Atmospheric O2 levels remained high and stable for tens of millions of years.•Insufficient O2 cannot explain late eukaryote emergence