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Written in Mud

Seafloor sediments often contain valuable clues to the nature of Earth’s climate in the distant past. Scientists collect long cores of sediment, sometimes from great depth, and then split them lengthwise. The mud contains the preserved shells of tiny surface-dwelling marine organisms that sank to the bottom and were buried over thousands of years. The shells contain clues to the chemical composition of the seawater in which they formed and, consequently, to the chemical composition of the atmosphere. The cores are then stored for other researchers working to learn more about Earth’s past climate. (Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)