Example cut from:
by Calvin J. Hamilton
Barringer Meteor Crater, Arizona35°02'N, 111°01'W; diameter: 1.186 kilometers (.737 miles); age: 49,000 years
The origin of this classic simple meteorite impact crater was long the
subject of controversy. The discovery of fragments of the Canyon Diablo
meteorite, including fragments within the
breccia deposits that partially
fill the structure, and a range of shock metamorphic features in the
target sandstone proved its impact origin. Target rocks include
carbonates and sandstones; these rocks have been overturned just outside
the rim during ejection. The hummocky deposits just beyond the rim are
remnants of the ejecta blanket. This aerial view shows the dramatic
expression of the crater in the arid landscape.
(Courtesy of D. Roddy and LPI)
Chicxulub, Yucatan Peninsula, Mexico
21°20'N, 89°30'W; diameter: 300 km; age: 64.98 million years
This three-dimensional map of local gravity and magnetic field
variations shows a multiringed structure called Chicxulub named after
a village located near its center. The impact basin is buried by
several hundred meters of sediment, hiding it from view. This image
shows the basin viewed obliquely from approximately 60° above the
surface looking north, with artificial lighting from the south. The
image covers 88 to 90.5° west longitude and 19.5 to 22.5°
north latitude (ca. 260 x 330 km). NASA scientists believe that an asteroid 10 to 20
kilometers (6 to 12 miles) in diameter produced this impact basin. The
asteroid hit a geologically unique, sulfur-rich region of the Yucatan
Peninsula and kicked up billions of tons of sulfur and other materials
into the atmosphere. Darkness prevailed for about half a year after
the collision. This caused global temperatures to plunge near freezing.
Half of the species on Earth became extinct including the dinosaurs.
(Courtesy of V. L. Sharpton, LPI)
Copyright © 1994, 1995, 1996 by
Calvin J. Hamilton. All rights reserved.