Mud Time Line Clarifies Dinosaurs' Demise

Article excerpt

A 16-inch core of mud tells the clearest story yet of how life on Earth suffered after a comet or meteor slammed into the planet about 65 million years ago, reports a team of oceanographers. Scientists drilled the sample from the ocean bed about 320 kilometers east of Jacksonville, Fla., earlier this year and reported their findings last week in Washington, D.C.

"This is the most significant discovery in geosciences in 20 years," says Robert W. Corell of the National Science Foundation in Arlington, Va., the primary funder of the expedition. Corell says that the sample ends the debate about what killed the dinosaurs.

That debate began in 1980, when scientists from the University of California, Berkeley discovered evidence that a chunk of rock the size of Manhattan slammed into Earth at the end of the Cretaceous period. At that time, an estimated 70 percent of Earth's species went extinct (see p. S20). The theory that the impact caused the mass extinction gained momentum after researchers discovered a 200-km-wide crater buried beneath the tip of Mexico's Yucatan Peninsula (SN: 3/5/94, p. 156).

The new mud core displays the entire time line of the catastrophic event with a clarity never seen before, says Richard D. …