Tar Pit Fossils Lie Under the Radar

It was more sticky wicket than groundbreaking moment Tuesday when scientists tried to use high-tech electronic imaging equipment to find prehistoric fossils buried in Los Angeles.

All that the ground-penetrating radar equipment scanning a subterranean area at the La Brea Tar Pits discovered was, well, tar.

It turns out that the gooey black tar that trapped Ice Age animals and preserved their bones also makes the resultant fossils invisible to ground radar -- much like special absorbent coverings make stealth fighters invisible to aerial radar.

And to top it off, heavy cellphone use along nearby Wilshire Boulevard and commercial radio broadcasts in the area were jamming the ground radar.

“I can see radio talk shows interfering with our signal here,” scientist Lawrence Conyers said as he studied his radar screen.

Tuesday’s experiment was aimed at determining if radar could be used instead of time-consuming, random -- often hit-or-miss -- digging to find prehistoric bones.

Researchers said the test proved that buried deposits of tar could be located by ground radar. And tar, after all, is where the fossils are found, said John Harris, chief curator and head of the Natural History Museum of Los Angeles County’s vertebrate studies division.

Conyers, a University of Denver anthropology professor who also is an expert on geology and geophysics, provided the $35,000 worth of imaging equipment and conducted the experiment without charge.

A pioneer in the use of ground radar in what he calls “noninvasive archeology,” Conyers has used his gear to pinpoint a Mayan village buried under volcanic ash, a 1,700-year-old buried settlement in Peru, and ancient pit houses used by Indians in Utah.

Ground-penetrating radar is commonly used by engineers looking for pipes at construction sites, by transportation officials inspecting roadbeds and bridge supports, and in police investigations where buried bodies or evidence is being sought.

At the tar pits, a lunchbox-size radar antenna guided along the ground by Page Museum paleontologist Chris Shaw and anthropologist Manuel Flores pulsated radar signals into a lawn known as the Pit 61-67 Compound. It is west of the museum building.

Resembling a one-wheeled lawnmower being pushed methodically back and forth over the grassy area, the contraption was wired to a flat-screen monitor 20 feet away that displayed the outline of any object within 6 feet of the surface.

Conyers and Harris peered at the screen, whose unwavering lines suggested that nothing was hidden under the lawn. In actuality, the screen was depicting a thick deposit of tar beneath a layer of sand, soil and grass. Any fossils caught in the sticky mass were blending right in with the tar’s radar image.

“We’d hoped to see individual bones. But we don’t know what a bone looks like,” Conyers joked.

“We were in a pit on top of bones earlier today and didn’t see anything. Tar deposits are a total wipeout. You don’t see anything at all when you come across them. See how everything disappears; it’s all smeared.”

Harris said the bones have become totally impregnated by tar over the eons. That, along with their submersion in the asphaltic sediment, makes them invisible to radar.

Conyers speculated that the proliferation of cellular phone and broadcast radio signals in the Mid-Wilshire area might be interfering with the radar receiver. He said he would use special computer software in hopes of cleaning up radar signals recorded at the Pit 61-67 Compound.

What little he saw on the radar screen, however, was enough to signal to Harris that the test was not a waste of time.

“We found out what tar pit deposits underground look like,” he said. “We could well be digging right here in the future for fossils.”

Tuesday’s test was prompted in part by an upcoming Venezuelan archeology expedition. Even with the bone-imaging setback, the Wilshire Boulevard test indicated that there will be a role for radar when fossil excavation begins in the Lake Maracaibo region in late spring.

Harris and Shaw have been appointed to the Board of Scientific Advisors at the Foundation for Quaternary Paleontological Research, a consortium of scientists and oil-industry sponsors that heads the paleoecological investigation of fossil deposits in northern Venezuela.

Officials hope to establish a Page Museum-style research center in that country.

Still, Harris acknowledged that he wished space-age technology had uncovered more prehistoric secrets Tuesday.

“It would be nice to go ‘bing’ and see a bone pop up on the screen. But maybe that’s too much to ask for,” he shrugged.