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Science 22 May 1998:
Vol. 280. no. 5367, pp. 1250 - 1253
DOI: 10.1126/science.280.5367.1250
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Reports

Geochemical Evidence for a Comet Shower in the Late Eocene

K. A. Farley, * A. Montanari, E. M. Shoemaker, dagger C. S. Shoemaker

Analyses of pelagic limestones indicate that the flux of extraterrestrial helium-3 to Earth was increased for a 2.5-million year (My) period in the late Eocene. The enhancement began ~1 My before and ended ~1.5 My after the major impact events that produced the large Popigai and Chesapeake Bay craters ~36 million years ago. The correlation between increased concentrations of helium-3, a tracer of fine-grained interplanetary dust, and large impacts indicates that the abundance of Earth-crossing objects and dustiness in the inner solar system were simultaneously but only briefly enhanced. These observations provide evidence for a comet shower triggered by an impulsive perturbation of the Oort cloud.

K. A. Farley, Division of Geological and Planetary Sciences, California Institute of Technology, MS 170-25, Pasadena, CA 91125, USA.
A. Montanari, Osservatorio Geologico di Coldigioco, 62020 Frontale di Apiro, Apiro, Italy, and Ecole des Mines de Paris, Paris, France.
E. M. Shoemaker and C. S. Shoemaker, U.S. Geological Survey, 2255 North Gemini Drive, Flagstaff, AZ 86001, USA.
*   To whom correspondence should be addressed. E-mail: farley{at}gps.caltech.edu

dagger    Deceased.

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