The Changing Atmosphere

The increase in oxygen in the atmosphere, due first to disassocia-tion of water, and later to photosynthesis, developed slowly during the Precambrian because of initial reactions with surface materials 

The movement onto land and the subsequent evolutionary divergence involved a number of innovations including the development of mechanisms to enable plants to withstand atmospheric drought including cuticle, xylem, stomata, and intercellular spaces. All of these innovations occurred during the late Silurian and early Devonian around 400 million years ago (Raven, 1977). Evidently coinciding with these structural innovations came the evolution of compounds that aided both protection from UV-B and water-stress tolerance. 

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Field, C. B., Chapin III, F. S., Matson, P. A., and Mooney, H. A. (1992). Responses of terrestrial ecosystems to the changing atmosphere a resource-based approach. Annu. Rev. Ecol. System. 23, 201-235. 

Fig. 19-2 Depletion of Antarctic ozone during October between 1956 and 1985. (Reprinted with permission from R. S. Stolarski (1988). Changes in ozone over the Antarctic. In F. S. Rowland and I. S. A. Isaksen, "The Changing Atmosphere/ p. 112. John Wiley, Chichester.)...

The implication from both Pb and trace-metal data is that the marsh surface, exposed above the sea surface most of the time, behaves like an atmospheric collector and can be used to monitor the changing atmospheric flux of trace metals over time. 

Graedel, T. E., and Crutzen, P. J. (1990), The Changing Atmosphere, in Managing Planet Earth Readings from Scientific American Magazine, W.H. Freeman Co., New York. 

The range of characteristics of planets is likely to exceed our experience with the planets and satellites in our own Solar System by far. Models of planets more massive than our Earth - rocky Super-Earths - need to consider the changing atmosphere structure, as well as the interior structure of the planet. Also, Earthlike planets orbiting stars of different spectral type might evolve differently. Modeling these influences will help to optimize the design of the proposed instruments to search for Earth-like planets. 

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