Glen A. Izett

U.S. Geological Survey Emeritus

Email :


Ph.D., Geology, University of Alaska

B.A., Geology, University of Colorado

Current Project

Compiling for the internet a photo gallery of distal impact ejecta from selected impact structures. The compilation is now approaching five gigabytes in 1,200 annotated photo files.


Asteroid (5765) Izett = 1986 GU, Discovered 1986 April 4 by C.S. Shoemaker and E.M. Shoemaker at Palomar.

Named in honor of Glen A. Izett, an American geologist of many talents. Izett has carried out the most detailed studies of the Cretaceous-Tertiary boundary clay layers in the western United States and their implications for the great impact event that terminated the Cretaceous. He has also contributed the most precise determinations of the ages of tektites from the extensive Australasian strewn field. His work with John Obradovich on the ages of volcanic ashes and tektites has led to the most highly refined time scale for the reversals of the geomagnetic field in the late Quaternary. Asteroid (5765) Izett (15 km diam.) is in the middle of the main asteroid belt somewhat beyond the distance of the 3:1 commensurable motion of Jupiter. It is large enough to make a spectacular crater on Mars or a Chicxulub-size crater and an accompanying mass extinction event should it ever strike Earth. Most strikingly asteroid (5765) Izett has an inclination 31.4 degrees, which places it higher than the nu 5 secular resonance in a region of orbital element phase space populated by very few asteroids. Foregoing modified from citation of C.S. Shoemaker and E.M. Shoemaker, July 7, 1997, Flagstaff, Arizona.

Selected Publications

Izett, G.A., 1991, Tektites in Cretaceous-Tertiary boundary rocks on Haiti and their bearing on the Alvarez impact extinction hypothesis:  Journal of Geophysical Research, v. 96, no. E4, p. 20,879-20,905.

Izett, G.A., Dalrymple, G.B., and Snee, L.W., 1991, 40Ar/39Ar age of Cretaceous-Tertiary boundary tektites on Haiti:  Science, v., 252, p. 1539-1542.

Izett, G.A., 1993, The Manson impact structure--40Ar/39Ar  age and its distal impact ejecta in the Pierre Shale in southeastern South Dakota:  Science, v. 262, p. 729-732.

Izett, G.A. and Obradovich, J.D., 1994, 40Ar/39Ar age constraints for the Jaramillo Normal Subchron and the Matuyama-Brunhes geomagnetic boundary:  Journal of Geophysical Research, v. 99, no. B2, p. 2925-2934.

Izett, G.A., Cobban, W.A., Dalrymple, G.B., and Obradovich, 1998:  40Ar/39Ar of the Manson impact structure, Iowa, and correlative impact ejecta in the Crow Creek Member of the Pierre Shale (Upper Cretaceous),South Dakota and Nebraska: Geological Soc. America Bulletin, v., 110, no. 3, p. 361-376. Izett, G.A., and Obradovich, J.D., 2001, 40Ar/39Ar ages of Miocene tuffs in basin-fill deposits(Santa Fe Group, New Mexico and, and Troublesome  Formation Colorado) of the Rio Grande Rift system:  The Mountain Geologist, v. 38, p. 77-86.

Horton, J.W., and seven others including Izett, G.A., 2005, Recent research on the Chesapeake Bay impact structure, USA—Impact debris and reworked ejecta, in Kenkmann, T., Horz., F., and Deutsch, A., eds. Large meteor impacts III: Geological Society of America Special Paper, 384, p. 147-170. 

Horton, J. W., and Izett, G.A., 2005, Crystalline rock ejecta and shocked minerals of the Chesapeake Bay impact structure, USGS-NASA Langley Core, Hampton, Virginia with supplemental Constraints on the age of the impact, in Horton, J.W., and others, eds. Studies of the Chesapeake Bay impact structure—The USGS-NASA Langley Coreholes and Geophysical Surveys, USGS Prof. Paper 1688, p. E1-E24.