Meteorites: coming and going.

A meteorite appears to have blasted a mile-wide hole in the middle of Nebraska as little as 3,000 years ago.

While examining new topographic maps, researchers at the University of Kansas in Lawrence discovered a circular, 25-meter-deep depression that they suspect represents the weathered remains of an impact crater. Most of the apparent crater lies beneath farmland about 12 miles west of Broken Bow.

Weathering has eroded and filled in this feature, which the team believes was originally 75 to 100 meters deep. When new, the purported crater would have rivaled the better known Meteor Crater of Arizona, says team member Wakefield Dort Jr.

Scientists believe the 50,000-year-old Meteor Crater was formed by a meteorite approximately 40 meters across. While an impact of this magnitude would not have greatly affected global climate, local fallout may have been significant. The Kansas researchers found buried fragments of glass, which they believe represent material melted and ejected by the impact, more than a mile from the crater rim's edge.

The depression lies in loose silt that accumulated between 20,000 and 12,000 years ago. The researchers believe the impact occurred more recently, however, because they discovered the glass fragments resting in a soil layer about 3,000 years old.

The team plans to continue its investigation of this feature, searching in particular for direct evidence of an impact: namely, pieces of the actual meteorite.

Other researchers presented these findings about craters:

* Approximately 80 miles east of Atlantic City, N.J., scientists have located the site of a larger impact that occurred approximately 35 million years ago, reports geologist C. Wylie Poag of the U.S. Geological Survey in Woods Hole, Mass. The 9-mile by 15-mile crater is believed to have resulted from the impact of a meteorite that sent a giant wave crashing over coastal areas from New Jersey to North Carolina (SN: 11/02/91, p.286).

* Possible craters elsewhere were called into question. Elongated depressions in Argentina, formerly considered the result of a glancing meteorite blow (SN: 1/25/92, p.55), may in fact have resulted from wind erosion, says Arthur L. Bloom, a geomorphologist at Cornell University.