Summary

Much attention has been paid to the subject of silicate mineral weathering and how it relates to the evolution of atmospheric CO2. As a result, the overall rate of uptake of atmospheric CO2 over time is much better understood than the rate of release of CO2 via degassing (see chapter 4). In the present chapter all of the major factors affecting silicate weathering have been examined. This includes (1) physical erosion as affected by mean continental relief; (2) temperature, as affected by the atmospheric greenhouse effect; solar evolution, and continental drift; (3) rainfall and runoff as affected by the greenhouse effect and continental drift; (4) land vegetation, as it evolved over time, and (5) lithology, especially the difference in weathering rates between carbonates and silicates and granites and basalts. Rate expressions for all these factors were derived in this chapter and presented in terms of nondimensional factors which can be applied to carbon fluxes involved in the long-term carbon cycle.

Although weathering is better understood than degassing, there are still some outstanding problems: (1) Is there a better method for quantifying the role of physical erosion over time as it has affected chemical weathering? (2) How have changes in the size and distribution of the continents affected the temperature of rocks undergoing weathering and the degree of flushing of these rocks by rainfall? (3) How did the rise of large vascular land plants affect weathering rate? There have been only a limited number of studies on this topic. (4) How did the rise of angio-sperms affect weathering rate? This subject is poorly understood at present. (5) What is the quantitative effect of cosmic ray fluxes on climate and weathering? (6) How has the abundance of basaltic rocks exposed to weathering varied over time, and can the ratio of strontium isotopes in the oceans be used as a measure of basalt weathering? This all shows that there is still plenty to learn about silicate weathering and it how it affects atmospheric CO2 over geologic time.

Organic Gardening

Organic Gardening

Gardening is also a great way to provide healthy food for you and your loved ones. When you buy produce from the store, it just isnt the same as presenting a salad to your family that came exclusively from your garden worked by your own two hands.

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