Chapter 18 - Geochemical and Biological Consequences of Phytoplankton Evolution

Abstract

This chapter examines the role of marine photoautotrophs on Earth's carbon cycle, with an emphasis on the impact of these organisms on the redox changes inferred from the isotopic signals preserved in the geological record. The ““biological”“ or “fast” carbon cycle is biologically driven and is based on redox reactions, which are at the core the fundamental chemistry of life. A critical point in the discussion of the Wilson cycle is the exchange between oceanic crust and cratons. This is followed by a review of the macroevolutionary trends of marine phytoplankton. There is a clear link between the history of phytoplankton evolution and the carbon cycle. The third section of the chapter considers the carbon isotopic records in carbonates and organic matter throughout the Phanerozoic. In the chapter, the author has suggested that there may be a causal relationship between the large-scale tectonics of the current Wilson cycle and biogeochemical cycles driven, at least in part, by changing phytoplankton community structure. The chapter gives a closer look at past Wilson cycles, macroevolutionary changes, and biogeochemical cycles. Carbon isotope records provide critical information that can be used to reconstruct changes in redox conditions and biological processes that affected past atmospheric and seawater chemistry. Carbon isotope records of carbonates and organic matter are used in conjunction with sulfur isotopes of sulfates, in model simulations to reconstruct carbon burial, pCO2, and pO2. These model results indicate that organic carbon burial and pO2 have increased since the Early Jurassic, whereas pCO2 has decreased since the Early Cretaceous.