Shorelines are ephemeral boundaries that might serve as a forest floor or a seafloor thousands of years from now. What will happen to present shorelines is determined thousands of miles away, by the behavior of continental ice sheets in Antarctica and Greenland. To investigate the timing and magnitude of past sealevel changes and their relationship to the waxing and waning of ice sheets over the past 25 million years, scientists working for the Ocean Drilling Program are beginning to collect sediment and rock samples below the ocean floor off the coast of New Jersey, near the edge of the continental shelf. Scientists from seven countries will extract more than two miles of cores from an immense pile of sediments that accumulated on the ocean floor over millions of years. By analyzing the sedimentary layers, researchers will document the precise timing and scale of sea level changes, which are hypothesized to result from the advance and retreat of continentsized ice sheets that stored and released water during climate cycles.