Sea Level Variations over Geologic Time

Sea level changes have occurred throughout Earth history. The magnitudes and timing of sea level changes are extremely variable. They provide considerable insight into the tectonic and climatic history of the Earth, but remain difRcult to determine with accuracy. Sea level, where the world oceans intersect the continents, is hardly Rxed, as anyone who has stood on the shore for 6 hours or more can attest. But the ever-changing tidal Sows are small compared with longer-term Suctuations that have occurred in Earth history. How much has sea level changed? How long did it take? How do we know? What does it tell us about the history of the Earth? In order to answer these questions, we need to consider a basic question: what causes sea level to change? Locally, sea level may change if tectonic forces cause the land to move up or down. However, this article will focus on global changes in sea level. Thus, the variations in sea level must be due to one of two possibilities: (1) changes in the volume of water in the oceans or (2) changes in the volume of the ocean basins.