Earth's evolution, its climate history, and the history of life are archived in the chemical and isotopic compositions of marine and terrestrial sediments and fossils found within them. This information provides evidence for crus-mantle recycling, bolide impacts, mass extinction events, gas hydrate expulsion, climate cycles, and much more. Much of this geochemical evidence, such as the discoveries of oxygen isotope cycles in Quaternary sediments, enhanced iridium at the Cretaceous/Paleocene boundary, and relationships between near-trench sediments and associated arc volcanics, have overturned paradigms, opened new avenues of inquiry, and helped launch international research programs (e.g., Deep Sea Drilling Project ). In addition to revealing much about important Earth events and processes, geochemical records preserved in marine and terrestrial sediments are increasingly important for correlation of global records; indeed, for Precambrian and anoxic sediments, chemical and isotopic methods are indispensable and provide the main basis for correlation.