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We obviously agree with Wu et al. that H 2 O 2 might accumulate in the Archean land waters devoid of Fe 2+ . We do disagree on the topic of the half-life of H 2 O 2 , as the work cited in support for a longer half-live is not relevant to the conditions in the Archean ocean. While the existence of radicals in quartz is not in doubt, we do question the hypothesis that these radicals oxidize water to HO • and H 2 O 2 ., Competing Interests: Declaration of competing interest There is no conflict of interest., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

We address the chemical/biological history of H 2 O 2 back at the times of the Archean eon (2.5-3.9 billion years ago (Gya)). During the Archean eon the pO 2 was million-fold lower than the present pO 2 , starting to increase gradually from 2.3 until 0.6 Gya, when it reached ca. 0.2 bar. The observation that some anaerobic organisms can defend themselves against O 2 has led to the view that early organisms could do the same before oxygenic photosynthesis had developed at about 3 Gya. This would require the anaerobic generation of H 2 O 2 , and here we examine the various mechanisms which were suggested in the literature for this. Given the concentration of Fe 2+ at 20-200 μM in the Archean ocean, the estimated half-life of H 2 O 2 is ca. 0.7 s. The oceanic H 2 O 2 concentration was practically zero. We conclude that early organisms were not exposed to H 2 O 2 before the arrival of oxygenic photosynthesis., Competing Interests: Declaration of competing interest There is no conflict of interest., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)