By Sid Perkins
Normal 0 false false false MicrosoftInternetExplorer4 For the first time, researchers have assembled a comprehensive record of sea level variations during the Paleozoic Era, producing a nearly-300-million–year timeline that more than doubles previous chronicles for such fluctuations.
Many of the variations, some as much as 100 meters, could have been caused by geological processes other than the formation of massive, land-based ice sheets, the scientists speculate in the Oct. 3 Science.
The geological record is replete with evidence of rising and falling sea levels, such as the interleaving, or alternating, of rock layers derived from soil with those composed of ancient marine sediments. Determining the age of such a rock formation provides a snapshot of where sea level sat when the layers were deposited, says Bilal Haq, a marine geologist at the National Science Foundation in Arlington, Va.
Until now, however, no one had pieced together those snapshots to make a kind of movie that tracked ancient sea level through what scientists call the Paleozoic Era. That interval extends from about 542 million years ago, the beginning of the Cambrian Period — an era that saw life’s diversity proliferate — until the end of the Permian Period about 251 million years ago, when Earth suffered one of its largest mass extinctions (SN: 2/1/97, p. 74).