Sticking Around

The La Brea Tar Pits

How much do you know about the Angelenos of the Pleistocene?

FANCY TAR?
Hancock Park, an affluent area of Los Angeles, is well known for its celebrity sightings, million-dollar homes, and the famous Hollywood sign in the distance. But some of the neighborhood’s “residents” are even cooler. World-famous fossils—like the extinct dire wolf, saber-toothed tiger, and Columbia mammoth—are among the millions of specimens that have been excavated from the La Brea tar pits. Located on Wilshire Boulevard in the Miracle Mile, the tar pits contain one of the richest deposits of late Pleistocene era (the last ice age) fossils in North America. The fossils date from 10,000 to 40,000 years ago, and more than three million of them—including plants, mammals, birds, lizards, and insects—have been excavated since paleontologists first began digging there in the early 1900s.
The tar pits on display today were once excavation sites where workers dug for asphalt or scientists dug for fossils. Over the years, humans dug more than 100 pits throughout Hancock Park, but most of them have been refilled with dirt, debris, asphalt, and water. About 13 tar pits remain—the largest, called the Lake Pit, measures 28 square feet and is approximately 14 feet deep.
STICKY, GOOEY DEATH TRAPS

The La Brea tar pits formed thousands of years ago, when gas and oil beneath the ground came under pressure. The molten mixture pushed up through vents in the earth’s crust. Once it reached the surface, the oil pooled in natural depressions aboveground. The lighter part of the pooling oil evaporated—left behind was a heavy, sticky oil. Then rain and underground springs added water, forming ponds and lakes on top of the oil and creating what we now call the tar pits.

The water on the tar pits’ surface was especially attractive to thirsty animals, and during the warm spring and summer, the thick oil underneath was especially sticky. Animals that ventured into to the pits couldn’t escape. Often predators chased their prey into the pits and got stuck too. Paleontologists once found a large bison fossil surrounded by a pack of fossilized wolves. The dead animals eventually sank completely, and their bones and teeth turned brown from the oil. But otherwise, they were almost perfectly preserved for more than 30,000 years.
THOSE STRANGE CATTLE BONES
Hundreds of years ago, local Native Americans used the thick oil at the tar pits as waterproof caulking for their baskets and canoes. When the Spanish arrived in the 18th century, they used it to waterproof their houses. In 1828 the tar pits were part of a Mexican land grant called Rancho de la Brea (brea means “tar” in Spanish). When the United States took over California in 1848, the area was part of the deal, and ultimately, it came into the possession of lawyer and surveyor Henry Hancock and his family. The Hancocks sold the oil from the tar pits, and their workmen often found fossils, which they assumed to be the bones of unlucky cattle. It wasn’t until 1875 that a geologist identified a collection of bones as belonging to a saber-tooth tiger that had been extinct for 10,000 years.

By 1906 a paleontologist from UC Berkeley named John C. Merriam was busily excavating fossils from Rancho de la Brea. He published a paper on his findings and listed so many different types of prehistoric animals that the tar pits became a focus of study for paleontologists around the world. In 1913 fossils from the La Brea pools went on display at the newly opened Los Angeles County Museum of History, Science, and Art, and three years later, the Hancock family donated the tar pits to Los Angeles County. Scientists have been studying them ever since.
PALEONTOLOGY IS THE PITS

So many fossils have been discovered at the La Brea tar pits that scientists call the last 300,000 years of the Pleistocene era the “Rancholabrean land mammal age.” Thanks to the sticky pits, we now know that, during the ice age, creatures like saber-tooth cats, mammoths, long-horned bison, horses, bears, wolves…even camels and lions once prowled what is now Wilshire Boulevard. In 2006 workers were digging up ground along Wilshire Boulevard to enlarge a parking lot when they found Zed, a Columbian mammoth skeleton that was 80 percent complete, resting in what used to be a riverbed. Work on the parking lot was halted to allow the creature (and his 10-foot tusks) to be excavated.
But it’s not just the exotic animal fossils that excite scientists. Tiny bugs, with their wings still attached, have been preserved in the oil. And the partial skeleton of an 18-to 25-year-old woman shows that humans were living in L.A. more than 9,000 years ago. The skeleton from the tar pits is known as “La Brea Woman,” and she’s earned the distinction of being “the oldest Californian.”

Plant fossils are also important. The oldest La Brea fossil is a piece of wood that dates back 40,000 years. By examining the plant material (even pollen has been preserved in the oil), scientists are able to tell that, during the last ice age, Los Angeles was cooler and moister than it is now. Redwoods that prefer the foggy climate of the Northern California coast once thrived in Hancock Park.
IT’S ALIIIIVE!
Of course, what all these great discoveries of La Brea have in common is that they’re dead. Very few things actually live in the tar pits—there is an insect called the oil fly that lays its larvae there. But in 2007, environmental scientists at UC Riverside found another living creature where it wasn’t expected.

The researchers were studying the large bubbles of methane that appear on the tar pits’ surface. They took samples of oil from the pools and looked to see if they could find any bacteria that might be creating the methane. To their surprise, they found more than 200 types of as-yet-undiscovered bacteria living in the oil. These bacteria were eating the oil and excreting methane gas that bubbled up to the pits’ surface. One of the bacteria is related to a type that survives 50 miles above the surface of the earth, where ultraviolet rays sterilize almost everything else. Another resembles bacteria that can withstand high levels of radiation. Scientists hope these bacteria will help them understand how life can exist in extreme environments, including those on other planets. Researchers also hope that studying the oil-munching bacteria may lead to their use in cleaning up oil spills. And so it seems that even after decades of excavation at the tar pits, scientists still never know what they’ll dig up next.