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Can someone explain: > 800 million Carbon dioxide levels fall to the point at which C4 photosynthesis is no longer possible.[57] Without plant life to recycle

by h4kor 8y ago

Can someone explain: > 800 million Carbon dioxide levels fall to the point at which C4 photosynthesis is no longer possible.[57] Without plant life to recycle oxygen in the atmosphere, free oxygen and the ozone layer will disappear from the atmosphere. All multicellular life will die out.[58]

philipkglass 8y ago
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
foobiekr 8y ago
contiued silicate rock weathering which sequesters carbon dioxide
apo 8y ago
Photosynthesis produces oxygen at a rate faster than the rate of depletion due to oxidation of the Earth's crust (think rust). Without plants there's nothing left to spew oxygen back into the atmosphere. Photosynthesis converts CO2 into carbohydrates. Lowering the concentration of atmospheric CO2 slows this reaction. Plants also metabolize carbohydrates, producing CO2. So photosynthesis requires the right balance of CO2 concentration and light. The estimate for when CO2 levels would fall too low appears to come from the following linked article: The latter authors feared that photosynthetic production would cease ~ 0.1 Gyr from now when just 150 ppm CO2 remained in the atmosphere. The latter figure corresponded to the CO2 compensation point, at which photosynthetic carbon fixation would exactly balance losses through respiration. We stress that _ this must not be confused with the CO2 value at which healthy metabolism ceases; with zero net C fixation available, a plant could not repair itself, produce seeds, or even grow. https://arxiv.org/pdf/0912.2482.pdf https://arxiv.org/pdf/0912.2482.pdf There's more on the compensation point here: https://en.wikipedia.org/wiki/Compensation_point https://en.wikipedia.org/wiki/Compensation_point

by h4kor 8y ago

philipkglass 8y ago

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

foobiekr 8y ago

contiued silicate rock weathering which sequesters carbon dioxide

apo 8y ago

Photosynthesis produces oxygen at a rate faster than the rate of depletion due to oxidation of the Earth's crust (think rust). Without plants there's nothing left to spew oxygen back into the atmosphere. Photosynthesis converts CO2 into carbohydrates. Lowering the concentration of atmospheric CO2 slows this reaction. Plants also metabolize carbohydrates, producing CO2. So photosynthesis requires the right balance of CO2 concentration and light. The estimate for when CO2 levels would fall too low appears to come from the following linked article: The latter authors feared that photosynthetic production would cease ~ 0.1 Gyr from now when just 150 ppm CO2 remained in the atmosphere. The latter figure corresponded to the CO2 compensation point, at which photosynthetic carbon fixation would exactly balance losses through respiration. We stress that _ this must not be confused with the CO2 value at which healthy metabolism ceases; with zero net C fixation available, a plant could not repair itself, produce seeds, or even grow. https://arxiv.org/pdf/0912.2482.pdf https://arxiv.org/pdf/0912.2482.pdf There's more on the compensation point here: https://en.wikipedia.org/wiki/Compensation_point https://en.wikipedia.org/wiki/Compensation_point