On 2017 Apr 07, Tanai Cardona commented:

Quite an interesting article.

On page 16, you say: "However, several lines of evidence are consistent with the existence of oxygenic photosynthesis hundreds of millions of years before the Archean–Proterozoic boundary [...]"

Another line of evidence for an early origin of oxygenic photosynthesis comes from the evolution of the photochemical reaction centers and Photosystem II, the enzyme that oxidizes water to oxygen. I have recently shown that the earliest events in the evolution of water oxidation catalysis likely date back to the early Archaean. See Cardona, 2016, Front. Plant Sci. 7:257 doi: 10.3389/fpls.2016.00257; and also Cardona et al., 2017, BiorXiv, doi.org/10.1101/109447 for an in depth follow up.

I am very glad to read that a largely anaerobic Archaean atmosphere with oxygen levels as low as 10E-7 is not inconsistent with the presence of oxygenic photosynthesis.

On 2017 Apr 07, Tanai Cardona commented:

Quite an interesting article.

On page 16, you say: "However, several lines of evidence are consistent with the existence of oxygenic photosynthesis hundreds of millions of years before the Archean–Proterozoic boundary [...]"

Another line of evidence for an early origin of oxygenic photosynthesis comes from the evolution of the photochemical reaction centers and Photosystem II, the enzyme that oxidizes water to oxygen. I have recently shown that the earliest events in the evolution of water oxidation catalysis likely date back to the early Archaean. See Cardona, 2016, Front. Plant Sci. 7:257 doi: 10.3389/fpls.2016.00257; and also Cardona et al., 2017, BiorXiv, doi.org/10.1101/109447 for an in depth follow up.

I am very glad to read that a largely anaerobic Archaean atmosphere with oxygen levels as low as 10E-7 is not inconsistent with the presence of oxygenic photosynthesis.