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In the minds of the broad public, carbon dioxide is associated primarily, if not exclusively, with considerations of global warming. This topic has been the focus of undoubtedly great attention in the last decades of the 20th and in the early 21st century owing to the coverage of the subject of global warming and climate change by the news media drawing their information from the results of scientific studies. The role of carbon dioxide as one of the gases that warm the Earth’s atmosphere by absorption of infrared or longwave, outgoing Earth radiation has been known since the work of the French scientist Jean-Baptiste-Joseph Fourier in the early nineteenth century and that of the Irish polymath John Tyndall in the middle part of that century.

In this chapterwe discuss Earth’s early prebiotic history and the conditions underwhich life emerged. The chapter focuses in particular on the sources and fate of the volatiles that degassed from the Earth’s interior and formed its atmosphere, hydrosphere, and sedimentary rocks, giving rise to the global carbon cycle. The chapter also discusses the cooling history and compositional changes of the primordial atmosphere and the early oceans up to the time when life appears. The environmental conditions and the material and energy sources of the early organismal groups are primarily inferred from those of the chemosynthesizing and photosynthesizing organisms of the present.

It is well known that the temperature of the Earth’s surface without the atmosphere would have been much colder and probably not suitable for life in the form as we know it. As the conditions on the surface of the two nearest neighboring planets, Venus and Mars, are very different from those on Earth and no life has yet been detected outside our planet, it is difficult to dispute the view that life on Earth is tied to the presence of liquid water and a gaseous atmosphere within the range of temperatures and pressures that characterize the terrestrial near-surface environment.

Among the carbon-containing minerals, the carbonates are by far the most abundant in the outer shell of the Earth. Elemental carbon, in the mineral forms of diamond and graphite, forms at higher temperatures and pressures. Occurrences of mineral carbides, such as silicon carbide moissanite (SiC), in terrestrial rocks are rare, but several metal carbides have been found in meteorites (Bernatowicz ., 1996; Di Pierro ., 2003). There are salts of organic acids classified as minerals, either containing metal cations or without them, that occur as alteration products in organic-matter-rich sediments or on other minerals that were probably subject to bacterial alteration.

This chapter presents some of the basic physical and chemical relationships that are relevant to an understanding of the behavior of CO in the Earth’s surface environment. It would be an understatement to say that the literature on this subject is extensive—it is prodigious! In Chapter 2 we dealt with the Earth’s atmosphere in the past and present that is based mostly on the model of an ideal gas. However, CO on the Earth’s surface interacts with other gases, it dissolves in water, and reacts with water, other dissolved species, and minerals. Many of the chemical reactions involving CO are either directly or indirectly mediated by biological processes, as is briefly discussed in Chapter 1 and further addressed in Chapters 6 and 9.

Stable and radioactive isotopes are extensively used as tracers of numerous processes in the planetary and terrestrial environment. The relative abundances of isotopic species measured by their ratios provide indications of the origin of various materials and differences in the abundance ratios that develop in different processes make it possible to identify the mechanisms behind a variety of phenomena in extraterrestrial space, within the solid Earth, on its surface, and in the biosphere. The improvements in the sensitivity and precision of mass spectrometers used for the determination of isotope abundances are continually expanding the number of isotopes that can be identified in natural materials aswell as the understanding of the mechanisms that drivemany parts of the Earth’s system. The involvement of carbon dioxide in many geochemical inorganic as well as biogeochemical processes focused long ago attention on the behavior of the different isotopic species of CO and made possible many new interpretations of processes in the atmosphere, on land, in the oceanic and continental waters, and within the biosphere. The goal of this Chapter is to review the essentials of the isotope geochemistry of carbon dioxide and the mechanisms of its isotopic fractionation, and to discuss the broader aspects of the global carbon cycle that are based on the carbonisotope geochemistry.

In Chapter 2 we discussed some aspects of the beginnings of the carbon cycle and Precambrian atmospheric CO2 concentrations. The major conclusions, among others, were that (1) atmospheric CO2 levels were relatively high at that time and they provided a necessary greenhouse warming in the period of the faint young Sun, in addition to the possible presence of higher concentrations of other potential greenhouse gases and aerosols (e.g., CH4 and organic volatiles) in the Hadean and early Precambrian atmosphere; (2) because of the high atmospheric CO2 levels, the early oceans were rich in dissolved inorganic carbon and total alkalinity, had a relatively low pH, and might have been depleted in dissolved Ca; and (3) as Precambrian time progressed, carbon was removed from the atmosphere and stored mainly in the large geochemical reservoirs of inorganic and organic carbon.

Carbon dioxide dissolved in rain and soil and ground waters is the main acid that reacts with minerals in the sedimentary and crystalline crust, releasing the ionic constituents of river water and producing the bicarbonate ion, HCO, in the process. The consumption of CO in mineral weathering reactions is a major transfer path of CO from the atmosphere to the land in the carbon cycle. On land, CO is bound in organic matter by plant photosynthesis, and released into the soil pore space by the remineralization of organic matter.

In this chapter we address the behavior of inorganic and organic carbon in the shallow coastal ocean where a large part of the biological production and sediment accumulation occur. At present, the coastal zone is more or less synonymous with the continental shelf that is covered by ocean water as a result of ice melting and sea level rise of 120 meters since the end of the Last Glacial Maximum about 18,000 years ago. In some intervals of the geologic past, shallow epicontinental seas were much more widespread during the periods of marine transgressions when the land was covered by seawater due to a rising sea level, caused by such factors as change in the relative elevation of land and(or) displacement of the ocean-water volume by the growth of spreading ridges on the ocean floor. In fact, a large part of marine sediments preserved on the continents was formed in shallow seas of the past that covered parts of the cratons of what are now different continents. The importance of the coastal ocean in the regulation of the global carbon cycle is primarily related to its position at the junction of the land, atmosphere, and open ocean, with all of which it interacts differently and modifies the transport fluxes of carbon. We emphasize in this chapter the inorganic and organic carbon cycles in the coastal ocean at the time scale of the Industrial Era, the last approximately 300 years, and up to three centuries into the future that are the time of increasing perturbations of the global carbon cycle by human activities.

In this chapter we review the evolution of the long-term behavior of the global carbon cycle through geologic time and some events of biological evolution and climatic change relevant to that behavior. A discussion of glacial-interglacial changes in the carbon cycle follows to provide background of carbon system behavior prior to major human interference in the carbon cycle. We utilize and emphasize portions of the previous chapters to present a coherent story of trends in the carbon cycle and events that took place and led to major reorganizations of the cycle. This material provides background for discussion in Chapter 11 of the modern carbon cycle and its drivers of nutrient N and P since major human interference in the cycle, a period of time that has become known as the Anthropocene.