SEAN BRENNAN
U.S. GEOLOGICAL SURVEY

"Seawater Chemistry and the Advent of Biocalcification, or the Chemical Origins of Seashells"

One of the most dramatic and confounding events in evolutionary and geologic history was the sudden onset of biomineralization in the Early Cambrian during the “Cambrian explosion”. Major ion compositions of primary fluid inclusions from terminal Proterozoic (ca. 544 Ma) and Early Cambrian (ca. 515 Ma) marine halites indicate that seawater Ca²⁺ concentrations increased approximately threefold during the Early Cambrian. This increase in the Ca²⁺ concentration of seawater may have created a chemical environment that was favorable for the onset of the development of calcium carbonate and calcium phosphate skeletons among metazoans.