Introduction

The preceding chapter focused on singular events in the later history of the Earth - the flowering of multicellular complex organisms at the start of the Phanerozoic eon and the widespread extinction of species some 65 million years ago at the close of the Cretaceous period. Although these events stand out in their drama and the mystery of their causes, any understanding of the interactive history of life and Earth's environment cannot rest on their study alone. Throughout the Phanerozoic, and before, the relatively steady rhythms of plate tectonics brought continental masses together and then moved them apart, creating new seafloor and destroying old. The process of great landmasses moving around the planet must have had profound effects on the environment, and indeed this is seen to be the case in the geologic record.

This chapter begins by reconsidering plate tectonics with an eye to understanding the apparently cyclical creation and break up of multicontinent landmasses, or supercontinents. We consider the effects of such supercontinent cycles on the amount of volcanic activity, and hence atmospheric chemistry, on the ocean circulation patterns, on mountain building, and hence on the available area for storage of continental snow and ice deposits. Such considerations touch on a major theme of the latter portion of Earth history, the comings and goings of great ice ages. Finally, we draw our attention in detail to a particularly warm time in recent Earth history, the Cretaceous period.