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This chapter discusses the history of atmospheric oxygen through geologic time. One of the giants in this discussion is Vladimir Vernadsky 1863–1945), a Ukranian mineralogist turned geochemist and visionary thinker. In 1926 he published his magnum opus The Biosphere, in which he systemically explored how life works as a geological force. One subject he touched upon was the history of atmospheric oxygen. He initiated this discussion by stating that in all geological periods, the chemical influence of living matter on the surrounding environment has not changed significantly. He concluded that the phenomena of superficial weathering clearly show that free oxygen played the same role in the Archean Era that it plays now. The chapter then explores early Earth biology, focusing on signs of cyanobacteria, without which oxygen could not have accumulated into the atmosphere.

This chapter provides an introduction to fossils and a geologic time frame, which provides a context for interpreting marine mammal fossils and possible causes for their origin and diversification. The evolution of marine mammal communities through space and time are considered, as well as what may have led marine mammals back to the sea. The use of stable isotope technology is explored for ecologic studies that range from reconstructing paleotemperatures and climate change to documenting diet and foraging ecology among both living and fossil marine mammals.

This essay reviews the book Annals of the Former World, by John McPhee. First published in 1998, Annals of the Former World presents a geological history of North America. The book is a compilation of writing on geology McPhee began in 1978 when he published a short item about a road cut on Interstate 80 west of New York City. Over the following twenty years, that initial story led McPhee to make a series of trips across America in the company of geologists, through whom he would explore both the geologic history of a region and the history of geology itself. Those travels resulted in four separate books: Basin and Range, In Suspect Terrain, Rising from the Plains, and Assembling California. For the publication of Annals of the Former World, these were joined by a fifth and final section, Crossing the Craton. McPhee invokes the notion of “animal time”—as opposed to geologic time—to illustrate how humankind stands in relation to the larger sweep of events.

This chapter explores the host of mechanisms involving biological and physical processes in the context of the evolution of ocean chemistry on geologic time scales. Large fluctuations in the salinity of the ocean are unlikely to have occurred, although periods following the deposition of evaporite “giants” may have been anomalously low in salinity. The Ca concentration and alkalinity of the ocean are regulated by the sensitive response of the ocean’s calcium carbonate compensation depth to variations in the oceanic C_aCO₃ saturation state. Potential metal toxicity is prevented by the production of specific metal-binding ligands by the marine biota. Overall, the system is resilient, but human activity may be perturbing important state variables of the ocean to an extent that will be detrimental to marine life.

This chapter examines scientific ideas that led to the theory of deep time, with particular emphasis on the work of William Thomson, later Lord Kelvin. Kelvin used the laws of physics to reject Charles Lyell's theory of uniformitarianism to explain an eternal, unchanging Earth. The first law of thermodynamics holds that in any process, energy in the form of heat and work is conserved. The second law can be stated simply as: heat flows spontaneously from hotter to colder places, never the opposite. In describing geologic time as infinite and the Earth as unchanging, Lyell claimed that the Earth is a perpetual-motion machine, one that can not only win the energy battle but go on doing so forever. But the first and second laws of thermodynamics prove that such a machine is impossible. According to Kelvin, Lyell's theory “violates the principles of natural philosophy.” This chapter considers Kelvin's argument about the age of the Earth and how he pushed geology toward the twentieth century.