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Giant Meteorite Hit Ancient California, Crater Study Suggests

John Roach
for National Geographic News
March 27, 2007
 
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.

Science Fair

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.

Samuel Spevack partnered with Morrow for the continued analysis. The researchers are searching for deformities in the rocks, such as shocked quartz, that require the high-shock pressure of impacts in order to form.

"We've found a few grains that exhibit some features of shock, but there still needs to be other searching and peer reviewing," Samuel Spevack said.

David Kring is an expert on impact craters at the Lunar and Planetary Institute in Houston. He said the presentation at the conference was appropriate for this stage of the crater analysis, but more rock analysis is required "to confirm an impact origin."

"The reason that's important is [that] there are a lot of geologic processes that make circular structures," he added.

Headline Impact

According to Bennett Spevack, if a space rock did crash into California's Central Valley, it would have created a 1,500-megaton explosion.

"This is not big enough to have wiped out the dinosaurs, but I guess it certainly would have made headlines if one this size would hit San Francisco," he said.

Scientists believe California's Central Valley was underwater at the time of the possible meteorite strike. If so, the impact may have also triggered a tsunami.

The proposed impact crater, called the Victoria Island structure, is being added to a database of suspected impacts. It joins the 0.8-mile (1.3-kilometer) Cowell structure to the north as California's only potential impact craters.

Neither structure is confirmed.

"If [the Victoria Island structure] can be proven, it'll be the first one in California," Bennett Spevack said.

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