4 - Chemistry of the early oceans: The environment of early life

Abstract

This chapter discusses chemistry of the ocean in relation to the origin and early evolution of life. The chapter emphasizes on how the early ocean could supply the energy and materials needed for extant life and also of putative ancestral organisms and prebiotic components. The chapter begins with an outline of the likely chemical composition of the Hadean Ocean, including changes to ocean chemistry because of interactions with the earth's crust and with the atmosphere. Furthermore, the chapter also considers the ways in which the Hadean Ocean could have supplied the materials and the energy needed for the origin and early evolution of life. This view focuses on ocean and atmosphere interactions as most significant in providing the energy for early life to the ocean. Later the direct use of light energy by organisms at the ocean surface became the major energy transforming reaction, providing energy for almost all living organisms. The chemical elements that were used by the earliest organisms were determined by their availability to early organisms as well as by their physicochemical appropriateness for particular biological functions. Modification of ocean chemistry by the activities of living organisms—for example, the accumulation of photosynthetically produced oxygen—changed the availability of several biologically essential elements. The chapter concludes with a discussion on how early life could have modified the chemistry of the ocean, and how these changes could have fed back to the evolution of the early organisms.