Cretaceous Crash

The theory called for a huge crater. Glen Penfield knew just where to look.

IF SCIENTISTS SOLVE THE MOST INTRIGUING mystery in paleontology—why the dinosaurs suddenly disappeared 65 million years ago—a share of the credit should go to Glen Penfield. And with new evidence showing up every few months, the solution seems likely, due to the obscure geophysicist who, while working for a Houston oil services firm, discovered a crucial clue: a huge eroded crater on the north shore of the Yucatán Peninsula.

“The dinosaurs had been doing just fine for one hundred and fifty million years,” says the 41-year old geophysicist. “All of a sudden, this think plowed into the earth. It created a kilometer-high tsunami wave that sloshed from Central Texas to Haiti and threw an enormous volume of debris into the atmosphere—more than thousands of Mount Pinatubo volcanoes going off at once.”

Many scientist are now persuaded that the aftereffects of the event Penfield describes—a meteor or comet six miles across, blasting into the planet at tremendous speed—wiped out the giant reptiles. Vindication seems close for Penfield, who has been trying for years to convince extinction theorists that the eroded crater he discovered fourteen years ago is the smoking gun that they have been searching for.

In 1978, Penfield, then employed by the Western Geophysical Company of Houston, was in Mérida, Mexico. He was reading charts of magnetic data recorded by sensitive instruments from a plane crisscrossing the Gulf off the Yucatán coast. As he scanned for evidence that might lead to an oil discovery for the client—Pemex, Mexico’s national oil company—a pattern emerged. Comparing adjacent strips, he saw a huge half-circle of magnetic disturbances centered on the village of Chicxulub (cheek-shoe-lube).

“When I put the onshore data with the offshore data, I had that kind of Ah-ha moment,” Penfields recalls. He recognized the magnetic signature of a buried impact crater some 120 miles across. “I still get goose bumps when I think about it.”

But while the evidence of a big crater was scientifically interesting, it had little to do with the business of finding oil. Although Penfield reported his discovery to Pemex, the information was considered proprietary and there was no urgent reason to publicize the find.

Then in 1908, a team of scientists, led by Luis and Walter Alvarez of the University of California at Berkeley, shocked the world with a strong, plausible impact theory of dinosaur extinction based on physical evidence. They suggested that a pall of dust and debris lofted into the atmosphere by a collision with an errant asteroid or comet had caused the mass extinction. In the lengthy constant darkness that a followed the impact, Earth’s ecosystems had collapsed.

The key piece of evidence for the theory was in the thin layer of clay between rock from the Cretaceous Period (rich in dinosaur fossils) and the Tertiary Period (no dinosaur fossils). Around the world the layer showed a high concentration of iridium, a metal that is rare on Earth but more abundant in asteroids and comets. The best explanation for this iridium concentration, the Berkeley team suggested, was an impact that pulverized the object.

The theory sparked a heated debate in scientific circles. If the theory was correct, everyone wanted to know, where was the on-hundred-mile-wide crater such an object should have left behind.

Glen Penfield immediately though of the buried crater he had discovered. He and Pemex researcher Antonio Camargo presented the Chicxulub data at a 1981 geophysical meeting in Los Angeles—to an audience of twenty. “The impact people weren’t following the oil exploration business,” Penfield laments.

Undaunted, Penfield decided to prove his claim, only to be told that the evidence he needed—the core samples from exploratory wells drilled in the Yucatán in the fifties—had been destroyed.

Meanwhile, the impact hypothesis had gained more converts. Various sites for the killer meteor crater were suggested throughout the eighties, but they were disqualified upon closer examination. Then, in 1990, at the Lunar and Planetary Science Conference in Houston, a team of Arizona researchers, led by Alan Hildebrands and William Boynton, argued that tsunami deposits near Waco, along with blobs of glass called tektites unearthed in Haiti, meant that the impact occurred between North America and South America. But they couldn’t say where.

Penfield’s luck finally turned. In the Houston audience was the Houston Chronicle ’s science writer, Carols Byars, who had worked at Western Geophysical at the time of Penfield’s discovery. Byars told Hidebrand about the Yucatán site, and the Arizona team quickly got in touch with Penfield. They tracked down an overlooked Chicxulub well-core sample, and sure enough, there was the impact-shocked quartz they had been looking for. Almost overnight, Chicxulub became the leading crater candidate. At the 1991 Lunar and Planetary Science Conference in Houston, Penfield re-presented the Chicxulub data to a packed house.

Although there are still many scientific doubters, evidence for Chicxulub continues to mount, and Penfield’s triumph may be at hand. In November, PBS stations across the country will broadcast The Dinosaurs!, which will feature Penfield and his discovery in the series’ fourth and final installment, an examination of the various theories about possible causes of the dinosaurs’ demise.

Penfield, who now works for a geophysical firm based in Pennsylvania, says that critical work lies just ahead. A consortium, including researchers from Pemex and the Mexican National University , is coordinating Chicxulub research. Plans are under way for seismic testing and drilling so that scientists can pinpoint the age and map the exact dimensions of Chicxulub. “I haven’t really been vindicated yet,” say Penfield, “but someday soon, people will really see what I’ve been talking about. It’s just a dazzling feature.”

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