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Carbon dioxide and the Goldilocks Principle

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NASA Goddard Space Flight Center

The “Goldilocks Principle,” like the Big Bang, has never been very popular, because it smacks of fine-tuning and Earth is special, and all that. Trouble is, facts are like rats, when you forbid people to teach about them, they don’t just go away.

From ScienceDaily:

Scientists have shown how geologic process regulates the amount of carbon dioxide in the atmosphere. Researchers have documented evidence suggesting that part of the reason that Earth has become neither sweltering like Venus nor frigid like Mars lies with a built-in atmospheric carbon dioxide regulator — the geologic cycles that churn up the planet’s rocky surface.

Like many other large mountain ranges, such as the great Himalayas, the Andes began to form during the Cenozoic period, which began about 60 million years ago and happened to coincide with a major perturbation in the cycling of atmospheric carbon dioxide. Using marine records of the long-term carbon cycle, Torres, West, and Li reconstructed the balance between CO2 release and uptake caused by the uplift of large mountain ranges and found that the release of CO2 release by rock weathering may have played a large, but thus far unrecognized, role in regulating the concentration of atmospheric carbon dioxide over the last roughly 60 million years.

Abstract The observed stability of Earth’s climate over millions of years is thought to depend on the rate of carbon dioxide (CO2) release from the solid Earth being balanced by the rate of CO2 consumption by silicate weathering1. During the Cenozoic era, spanning approximately the past 66 million years, the concurrent increases in the marine isotopic ratios of strontium, osmium and lithium2, 3, 4 suggest that extensive uplift of mountain ranges may have stimulated CO2 consumption by silicate weathering5, but reconstructions of sea-floor spreading6 do not indicate a corresponding increase in CO2 inputs from volcanic degassing. The resulting imbalance would have depleted the atmosphere of all CO2 within a few million years7. As a result, reconciling Cenozoic isotopic records with the need for mass balance in the long-term carbon cycle has been a major and unresolved challenge in geochemistry and Earth history. Here we show that enhanced sulphide oxidation coupled to carbonate dissolution can provide a transient source of CO2 to Earth’s atmosphere that is relevant over geological timescales. Like drawdown by means of silicate weathering, this source is probably enhanced by tectonic uplift, and so may have contributed to the relative stability of the partial pressure of atmospheric CO2 during the Cenozoic. A variety of other hypotheses8, 9, 10 have been put forward to explain the ‘Cenozoic isotope-weathering paradox’, and the evolution of the carbon cycle probably depended on multiple processes. However, an important role for sulphide oxidation coupled to carbonate dissolution is consistent with records of radiogenic isotopes2, 3, atmospheric CO2 partial pressure11, 12 and the evolution of the Cenozoic sulphur cycle, and could be accounted for by geologically reasonable changes in the global dioxygen cycle, suggesting that this CO2 source should be considered a potentially important but as yet generally unrecognized component of the long-term carbon cycle. – Mark A. Torres, A. Joshua West, Gaojun Li. Sulphide oxidation and carbonate dissolution as a source of CO2 over geological timescales. Nature, 2014; 507 (7492): 346 DOI: 10.1038/nature13030

See also: Copernicus, you are not going to believe who is using your name. Or how.


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