ABSTRACT
Some of the CO2 generated in energy metabolism of living organisms can be xed in insoluble carbonates. Indeed, a signi cant portion of the insoluble carbonate at the Earth’s surface is of biogenic origin, but another portion is the result of magmatic and metamorphic activity (see Bonatti, 1966; Skirrow, 1975; Berg, 1986). Direct biological incorporation of carbon in carbonates involves some bacteria, fungi, and algae as well as some metazoa. These carbonates can be deposited extraand intracellularly. The bacteria, including cyanobacteria, as well as some fungi that are involved, deposit calcium carbonate extracellularly (Bavendamm, 1932; Monty, 1972; Krumbein, 1974, 1979; Morita, 1980; Verrecchia et al., 1990; Chafetz and Buczynski, 1992). The bacterium Achromatium oxaliferum seems to be an exception. It has been reported to deposit calcium carbonate intracellularly (Buchanan and Gibbons, 1974; De Boer et al., 1971). Some algae, including certain green, brown, and red algae, and chrysophytes, such as coccolithophores (Lewin, 1965), deposit calcium carbonate as surface structures of their cells, and some protozoa lay it down as tests or shells (foraminifera). Calcium carbonate is also incorporated into the skeletal support structures of certain
sponges and invertebrates such as coelenterates (corals), echinoderms, bryozoans, brachiopods, and mollusks. In arthropods it is associated with their chitinous exoskeleton. The function of the structural calcium carbonate in each of these organisms is to provide support and protection. In all these cases, calcium and some magnesium ions are combined with carbonate ions of biogenic origin (Lewin, 1965). Figure 9.2 illustrates a massive biogenic carbonate deposit in the form of chalk, the White Cliffs of Dover, England.
