asphalt jungle

IckyjenlucIn 1769, Gaspar Portola, the Spanish governor of Baja California, led an excursion across the Los Angeles River and down what is now Wilshire Boulevard in modern-day La-La Land. According to a journal kept by one of the expedition members — a priest named Juan Crespi — the travelers "saw some large marshes of a certain substance like pitch, they were boiling and bubbling… and there is such an abundance of it that would serve to caulk many ships." This is the first recorded sighting of the famed La Brea Tar Pits.

The landscape has changed a bit since then. Okay, it's changed a lot. Shortly after I moved to Los Angeles this past April, we were driving down Wilshire Boulevard en route to the city's high-end shopping mecca, Rodeo Drive, when we passed a sign reading "La Brea Tar Pits." Initially I assumed it was an advertisement, but the Spousal Unit assured me that no, in fact, the tar pits were right there, just off Wilshire, and couldn't I detect that telltale whiff of methane in the air? So one of the most well-known U.S. sites for paleontological fossils is located smack in the middle of suburban sprawl, amid condominium complexes, a Rite-Aid, and various fast food joints like Baja Fresh, Koo Koo Roo and IHoP. You can admire the pretty Pleistocene fossils, then pop on over to LA's Disney-esque shopping complex, The Grove, stopping off at Whole Foods for some organic produce on the way home.

You'd think that with the place so close, and me being such a big science geek and all, it would be one of the first places I'd visit. Alas, you'd be wrong. We didn't get around to visiting the La Brea Tar Pits and accompanying Page Museum until last weekend, when fellow physics blogger Chuck (a.k.a., that lounging Lab Lemming from the Land of Oz) blew through town with his family, on their way to visit relatives elsewhere in the U.S.  We had a great time strolling through the exhibits, admiring the rather seedy (by now) animatronic mammoth, and placing bets on whether the ground sloth or the saber-toothed tiger would win their sculpted pitched battle. True, they are frozen in time in the Page Museum, but I maintain that the tiger is on the verge of victory: its enormous canines are in the perfect position to rip out the sloth's jugular.

Technically, that substance oozing out of the ground in Hancock Park isn't really tar (a byproduct of the distillation of coal or peat); it's asphalt, the lowest grade of crude oil. The bubbling is due to methane gas, a byproduct of the decomposing remains of plants and animals trapped in the pits, which turn into crude oil. Which explains the origins of the large petroleum reservoir, the Salt Lake Oil field, located just below the surface, north of Hancock Park. According to the museum's various informative placards, the oil was formed from marine plankton that found themselves summarily deposited in an ocean basin between 5 and 25 million years ago, and eventually time and pressure converted that organic matter into oil. Beginning some 40,000 years ago, petroleum began seeping to the surface around Hancock Park, forming hundreds of sticky pools of ooze. And the La Brea Tar Pits were born.

Anyway, for tens of thousands of years, animals would come sniffing around the pits — usually predators and scavengers drawn by animals already trapped in the tar, thinking them easy prey — and would in turn become trapped in the sticky ooze themselves. They would gradually get sucked down into the pit and asphyxiate, and over time their remains became fossilized as the lighter fractions of the petroleum evaporated, leaving the bones trapped in a more solid substance. And there they stayed, awaiting discovery by modern archaeologists thousands of years later.

The centerpiece of the La Brea grounds is a large Lake Pit outside, where methane gas still bubbles to the surface every few minutes or so, making the whole place smell like freshly laid asphalt. To capture the tragedy of senseless animal deaths, traumatizing young children in the process, the Lake Pit also features a diorama of a mammoth vainly struggling to free itself from the  muck, while what can only assume are its mammoth-y family members look on in helpless horror.

One might be forgiven for thinking, "C'mon, how hard can it be to get out of a tar pit?" After all, Arnold Schwarzenegger fell into the tar pits in Last Action Hero and just swam out and wiped himself clean. The museum knows we're thinking this, and has helpfully set up a terrific hands-on demonstration of just how sticky this gooey stuff really is. We struggled mightily to pull metal plungers of different sizes and weights out of a vat of molten asphalt. Point taken. And the pits have their own form of camouflage, since they're covered by a layer of water, or dirt, or dust. It would be very easy to think you were just strolling through a marshy sort of puddle, and suddenly find, too late, that there's sticky asphalt underneath.

The local Native Americans used the sticky asphalt as a glue and to waterproof their baskets and canoes. When Westerners arrived, they mined the tar and used it as a roofing material. From the beginning, bones were occasionally found in the tar, usually dismissed as belonging to unfortunate cattle who'd become trapped in the pits. It was not until 1875 that the geologist William Denton visited the tar pits and identified the canine tooth of a saber-toothed cat. The rest of the scientific community just ignored his conclusion. Timing is everything, and Denton was too far ahead of the curve. The first bona fide scientific excavation of the pits didn't begin until 1901, when William W. Orcutt, a geologist who was investigating oil resources in the vicinity, noted that the bones in the asphalt seeps belonged to many extinct species.  

And so the pillaging of these priceless artifacts began. Between 1905 and 1915, literally millions of bones were taken out of the ground. In 1913, the landowner, George Alan Hancock, feared that the fossils would be taken from the community and scattered widely. So he granted exclusive rights to excavate the fossil resources to Los Angeles County’s fledgling Natural History Museum—but only for two years. Between 1913 and 1915, museum crews made nearly a hundred excavations, collecting roughly a million bones. The work was messy, and not without its perils: excavators used boiling kerosene to clean the sticky bones, which would sometimes accidentally catch fire and singe the eyebrows of workers. But it was worth it. In all, the species count from the excavations in the early 1900s included 133 birds, 63 insects, 43 mammals, and 29 plants, plus a handful of amphibian, mollusk, reptile, and water flea species.

Surprisingly, there's a lot more fossils of carnivores and predators than there are of herbivores — roughly 9:1, nowhere near the ratio most likely typical of the animal population living in the area back then. Scientists think it's because of the aforementioned hypothesis that predators and scavengers were drawn to the scent of trapped, rotting corpses and became trapped themselves. That's the prevailing hypothesis among scientists, although predictably, those wacky Young Earth Creationists maintain that the tar pits are evidence of a global flood. Noah's Ark totally happened, dude! Just like in Evan Almighty! By their "logic" (note judicious use of scare quotes to indicate sarcasm), the high ratio of carnivore fossils is due to the fact that theyw ere carried there from somewhere else by a huge flow of water. The fact that the tar pits date back some 40,000 years and are therefore older than the supposed Young Earth by a factor of 4, is considered to be a trifling dating error, or some mischievous test of faith by the Deity. Sigh.

Anyway, the animals didn't seem to learn from their mistakes, which could explain why they eventually became extinct: camels, mammoths, mastodons, long-horned bison, and the saber-toothed cat are no longer found in North America, and Chuck informed me (and the museum exhibit confirmed) that the horse, originally native to the area, died out and was introduced to the region by Spanish settlers. The dire wolf, in particular, seems to have been a bit lacking on the brain trust front: skulls and fossilized remains of the dire wolf are among the most common finds in the La Brea tar pits (over 3000 found to date, and still counting), and the Page Museum has an entire wall displaying nothing but hundreds of dire wolf skulls recovered over the years.

There's one species that is not well represented among the fossilized remains recovered from the tar pits: homo sapiens. You'd never know that from how often the tar pits feature in various thrillers and murder mysteries. For instance, in the forgettable 1990 film Bad Influence, the two men try to cover up a murder committed by a third friend — why? misplaced guy loyalty, I guess — by tossing the dead woman into the La Brea tar pits, where she is discovered the following day. In fact, there has been only one human being recovered from the pits, known as La Brea Woman; carbon dating revealed she died some 9000 years ago.

Technically, just her skull and a few other bones were recovered, and even so, the femur was stolen in the 1970s while the remains were in transit from their original home at the Natural History Museum to the newly constructed Page Museum. (Jen-Luc Piquant wonders aloud what kind of sick mind would steal a fossilized femur, and then recalls that her pal El Finster brazenly sports a bona fide human skull on his bookshelf. Authorities might want to check his office for any missing fossilized remains.)

Anyway, scientists believe La Brea Woman didn't end up in the tar by accident: there's strong circumstantial evidence that she was murdered, her skull bashed in with a blunt instrument, most likely with an artifact conveniently found a few inches from where her skull was found. This makes her the first documented murder victim in Los Angeles. They killed her little dog, too: canine bones were also found near her remains. Other than that, very little is known about La Brea Woman; the most extensive discussion I could find was this 2006 article in the Los Angeles Times by Amy Wilentz. That's where I learned that the museum used to have an exhibit devoted entirely to La Brea Woman until just a few years ago, when the curator decided to remove it amid concerns of offending local Native Americans. Like many of the exhibits in this woefully under-funded museum, the original exhibit was a bit archaic, featuring mirrors and spotlights to create a "Pepper's Ghost" kind of illusion: people would see her skeleton, then the special effects would kick in to create a mannequin version of how she might have looked in life.

Wilentz's article also informs us that the skeleton on display wasn't actually La Brea Woman; after all, most of her remains weren't found. Instead, they obtained the body of "a modern Pakistani female" of similar age and height, treated the bones so they looked like the dark bronze color that typifies tar pit bones, shortened the femurs, and attached the original skull. And the artistic depiction of how she would have looked in real life? Not so much with the accuracy. Far from being, in Wilentz's words, "a young, attractive sensuous tanned brunette with long, long hair strategically covering her nipples," La Brea Woman was a bit on the homely side, and probably considered middle-aged by 20 (most "elders" from that period were around 30; life was cheap and very, very short in the Pleistocene). She had an ectopic tooth protruding above her lip — one of her few remaining teeth — and an impacted molar in her jaw. Yet her remains have inspired subplots in at least two novels: Michael Connelly's City of Bones, and Robert Masello's The Bestiary. Something about La Brea Woman and her all-too-human fate speaks to us across the ages.

One might assume that after nearly a century of digging, the La Brea Tar Pits would be picked clean by now, but such is not the case. The focus has merely shifted from the large skeletons of mammoths, ground sloths, and saber-toothed tigers, to birds, bone fragments, seeds, pollen, insects, fish, rodents, and other objects so tiny, it's hard to believe the scientists were even able to identify them. The focus of the museum's current excavation activities is Pit 91, measuring 28 square feet and descending about 14 feet into the earth. Every summer, the pit is open for business from June to the beginning of October, so visits can stand in a special observation area and watch local paleontologists and a few lucky volunteers sift through the muck armed with dental picks, trowels, small chisels and brushes, in search of fossilized treasure.

And what a treasure trove the pit continues to be! In 2006 alone, the teams collected over 1000 in two months, ranging from three saber-toothed cat skulls, four dire wolf skulls, bones from sloths, horses, bison, coyotes and birds, insects, and a few plant fossils.  (Since excavation of Pit 91 began in 1915, over 250,000 fossils have been recovered.) After the fossils are removed, the surrounding sediment is placed in screen baskets, then boiled in solvent to remove the asphalt, revealing a mix of sand, pebbles, small pieces of fossils, and microfossils like seeds. I feel for whoever has the thankless task for cleaning, sorting identifying and labeling this flotsam and jetsam.

Okay, I'm being prematurely dismissive: those bits and pieces can actually tell us a lot about the area during the Pleistocene, specifically, the habitats and climate (apparently LA was cooler and moister in the Pleistocene). Most recently, scientists have discovered 200-300 previously unknown species of bacteria, extremophiles who flourish in the harsh conditions of the asphalt pits: no water and very little oxygen, but loads of yummy toxic chemicals! They chomp away at the petroleum, breaking it down with special enzymes (e.g., polychlorinated biphenyls, or PCB) and then releasing the telltale methane that bubbles to the surface. (Technically, the bacteria suffer from gas and post-meal bloating, and no wonder, considering their diet.) A team from University of California, Riverside, led by David Crowley, identified the bacteria by sequencing recovered DNA. They froze the tar with liquid nitrogen and pulverized it into a powder, exposing the bacteria, and thus were able to extract the DNA. It's quite possible that this discovery could lead to new methods for cleaning up oil spills and enhancing oil recovery.

The tar pits have had more than their share of 15 minutes of fame in popular culture, usually in wildly speculative contexts, none so much as in 1997's Volcano, in which a volcano sprouts out of the Lake Pit and spews a river of hot lava down Wilshire Boulevard — no doubt engulfing loads of unsuspecting well-heeled shoppers. (Young Earth Creationists would most likely attribute this to the avenging hand of a wrathful Deity.) But the reality is haunting in its own quiet way, with no need for exaggerated pyrotechnics. Wilentz describes the museum, for all its noble educational intentions, as "an homage to an oil reserve where millions of creatures died," a structure that has been built "above what can only be described as a mass grave." The La Brea tar pits are LA's very own heart of darkness, the epitome of "Nature, red in tooth and claw." After all, asphalt doesn't much care how many species perish in its sticky depths.

4 thoughts on “asphalt jungle”

  1. The Tar Pits were totally cool! Actually, they were my second favorite thing about LA, right after the Getty. I only wish we’d had time to go to the museum when El Finster et al and I were out there for your wedding. I’m surprised there weren’t modern humans recovered from the pits though; it’s such a convenient disposal area, or at least it was before the condos and the IHoP moved in.

  2. Thanks for the blog on a geologic topic. Very interesting.
    I have one small nit-pick however. You say “awaiting discovery by modern archaeologists thousands of years later”. This indeed is the popular view, archaeologists and paleontologists are the same since both deal with long ago dead stuff. However the training is very different. Archeology is a branch of anthropology, the study of cultures. Paleontology is the intersection of geology and biology, the study of the earth and its past life. Admittedly the study of La Brea Woman hits the small overlap: the study of human bones to tell about the life of the owner is Physical Anthropology. (Too many words for a small mis-statement, sorry)

  3. No posting about the La Brea Tar Pits would be complete without some bozo commenter noting that that name means The The Tar Tar Pits. The full pedant snark goes,
    From the El Camino Real to La Callecita Street, the hoi polloi are entering PIN numbers into ATM machines to get money for GPS systems before heading for the La Brea Tar Pits.
    (El Camino Real, you know about if you live in LA; The Little Street Street is, or was, an actual street in San Diego.)

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