I couldn't find the 800 million year figure specifically in the cited source: https://arxiv.org/pdf/0912.2482.pdf https://arxiv.org/pdf/0912.2482.pdf The gener

I couldn't find the 800 million year figure specifically in the cited source: https://arxiv.org/pdf/0912.2482.pdf https://arxiv.org/pdf/0912.2482.pdf The general idea, I believe, is that the carbonate-silicate cycle will shift more toward carbonates over time. The Earth will warm substantially as the sun's luminosity increases over millions of years. Warmer conditions will accelerate the reaction of water and carbon dioxide with silicate minerals like magnesium and calcium silicates, shifting the equilibrium to favor more carbon-as-insoluble-carbonate and less carbon-as-available-CO2. Plant life will eventually go extinct from insufficient atmospheric CO2. I haven't spotted a discussion of oxygen loss in either citation 57 or 58. But "just" losing plant life would be enough to drive the extinction of most other multicellular life on Earth. https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_cycle https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_cyc... https://en.wikipedia.org/wiki/Sun#Main_sequence https://en.wikipedia.org/wiki/Sun#Main_sequence