for National Geographic News
A space rock the size of three football fields may have slammed into California more than 35 million years ago, according to a team of scientists that includes a high school student.
The proposed impact may have created the giant 3.4-mile-wide (5.5-kilometer-wide) craterlike formation that the team found buried 4,900 to 5,250 feet (1,490 to 1,600 meters) below sea level west of Stockton, California (see California map).
Rocks in the potential crater date to about 37 to 49 million years ago.
While the formation resembles an impact crater, the researchers said, they are continuing to analyze rocks from oil exploration wells dug in the region for telltale signs of a collision.
Jared Morrow, an assistant professor of geology at San Diego State University, presented preliminary details of the discovery earlier this month at the Lunar and Planetary Science Conference in Houston, Texas.
Samuel Spevack, a senior at Grossmont Middle College High School in El Cajon, California, is leading the continuing analysis and will discuss the project next month at a meeting of the American Association of Petroleum Geologists in Long Beach.
Samuel's father, Bennett Spevack, is a geologist with ABA Energy Corporation in San Diego. He first spotted the crater while examining seismic survey data of the Central Valley region.
"It looked interesting because it was circular," he said. "My son saw it and expressed interest in figuring out whether it might be an impact crater."
Samuel presented seismic data of the proposed impact crater at the Greater San Diego Science and Engineering Fair in 2005.
The data clearly shows a circular structure carved out of an ancient sea bed.
The high school student won an award at the fair, but the scientific community requires additional rock evidence before it can verify a new impact crater.
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