Geology Of La Brea Tar Pits

The La Brea Tar Pits, located near Hollywood, California, contain one of the universes greatest troves of Pleistocene dodos. Over one million castanetss have been recovered to so far. Dating from 38,000BC to 8,000 BC, the castanetss represent more than 420 species of animate being, including saber tooth Liberation Tigers of Tamil Eelams, dire wolves, and 140 species of workss.

Geologic History

Leafs and grass blew across the pitch, organizing a thin top bed indistinguishable to the environing land. Unsuspecting animate beings grazed right out into the material. The pitch rapidly trapped them; their frenetic battles merely engulfed them deeper and deeper. Their manic calls attracted carnivores, including the sabertoothed cat, which pounced on the helpless victims, merely to happen itself trapped by the same pitch.

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In all, research workers have identified more than 420 species of animate beings and about 140 species of workss.

Elephantine mammals ruled the Pleistocene. Imperial mammoths, largest of the elephant folk, stood 4.5 metres tall and weighed around 6,800 kilogram. Ground sloths the size of a rhinoceros ambled from tree to corner. Huge camels and bison grazed on the fields. A king of beasts the size of a grey bear.

Dire wolves were merely that – dire: About the size of ponies, they hunted in battalions. Over 1,600 of their skulls have been found here so far.

The pitch asphalt is particularly effectual for salvaging delicate bird castanetss, and has yielded the largest aggregation of fossil bird castanetss of all time: over 100,000 carefully excavated castanetss. The most impressive bird of the clip was Merriam’s elephantine condor with its 4-meter wingspread. For comparing, today’s California condor has a wingspread of about 2.9 metres.

The two long, cut downing Fangs stick outing from its upper jaw gave the sabertoothed cat its name. ( The giant land sloth had a particular brace of castanetss wrapping its cervix as protection from the long Fangs. ) Sometimes slackly called the sabertoothed tiger, these large marauders really belonged to a separate sub-family of the Felidae, called the Machairodontidae, now wholly nonextant.

Other exhibits in the museum include a two-thirds-scale traveling theoretical account of a woolly gigantic realistic plenty to direct little kids scampering behind parents. The reconstructed skeleton of a mastodon with immense curving tusks impresses everyone. The monolithic skeleton of the American king of beasts makes you glad you don’Ts have to worry about run intoing one on the walk back out to the auto.

Possibly most poignant is the aggregation of 404 dire wolf skulls neatly arranged in rows registering one wall. Look at these leftovers of battalion huntsmans long plenty and you start to acquire the icinesss.

It is more than a spot phantasmagoric that these pitch cavities are in the bosom of downtown Los Angeles, right on the “Miracle Mile” and a short walk from the sole dress shops of Rodeo Drive. The pitch cavities still bubble and belch from gas oozing up. In some topographic points the pitch is oozing and forcing under protective concatenation nexus fencings. Some childs ( and grown-ups ) go place with a fresh pitch surfacing on their colloidal suspensions.

Tar cavities signifier when petroleum oil seeps to the surface through crevices in the Earth’s crust; the light fraction of the oil evaporates, go forthing behind the heavy pitch, or asphalt, in gluey pools.

The castanetss on occasion found in the pitch were foremost thought to be those of luckless cowss.

Life in Los Angeles was slightly cooler and damp 40,000 old ages ago than it is today, as we can state by analyzing the works fossils from La Brea. Many of the workss and animate beings found in La Brea are indistinguishable or about indistinguishable with species that still live in the country — or that would be populating in the country had Los Angeles non acquire in the manner. Yet a figure of the big carnal species found at La Brea are no longer found in North America: native Equus caballuss, camels, mammoths and mastodons, longhorned bison, and saber-toothed cats.

In today’s ecosystems herbivores are much more abundant than carnivores. It is hence funny that at La Brea about 90% of the mammal fossils found represent carnivores. Most of the bird dodos are besides marauders or scavengers, including vultures, condors, bird of Joves, and giant, extinct, storklike birds known as teratorns. Why is this the instance? If a battalion of carnivorous mammals were to trail a lone quarry animate being into the pitch cavities, both marauders and quarry would go at bay. This would non hold to be a frequent happening — an norm of one major entrapment every ten old ages, over a period of 30,000 old ages, would be sufficient to account for the figure of dodos found at La Brea. Scavenging animate beings, drawn to feed on at bay animate beings, would hold a opportunity of acquiring trapped themselves. This would explicate the preponderance of carnivores and scavengers.


In the bosom of Los Angeles lies one of the universe’s richest Ice Age dodo sites. Countless workss and animate beings were trapped in sedimentations of natural asphalt and preserved as dodos. These dodos now provide us with an improbably complete image of what life was like as the Ice Ages drew to a stopping point between 10,000 and 40,000 old ages ago.

Ranging in size from elephantine gigantic skeletons to microscopic works remains, the dodos include one celled

beings; pollen, seeds, foliages and wood; clam and snail shells; insects and spiders; fish; toads, salamanders, and frogs; serpents, lizards and polo-necks; birds; and mammals – in all, more than 565 species.

Many of the big animate beings in the Rancho La Brea dodo sedimentations are now nonextant. While many of the works and little animate being species uncovered in Rancho La Brea are still found in southern California, some workss and animals no longer live here due to alterations in the clime and alterations due to human development.


Layers of crushed rock, sand, and clay were laid down by watercourses. These beds cover much older Marine sedimentary stones rich in crude oil oil. Motions in the Earth’s crust hold folded and cracked the older stones. Heat and force per unit area force the oil up easy through the clefts and onto the surface of the land. Shallow pools of gluey asphalt formed in low-lying countries such as watercourse beds. Oil continues to ooze up to the surface as it has for 100s of 1000s of old ages.

Contrary to popular belief, the “tar” that trapped the animate beings is non tar at all, but asphalt.

The Tar Pits

Summer’s heat dried the watercourses and warmed the semi-solid asphalt to a gooey liquid. It was during the summer that the workss and animate beings became at bay. During the winter, ice chest temperatures harden the asphalt. Winter and spring rains fill watercourses with sand and silt that bury the remains of workss and animate beings trapped in the shallow asphalt pools. The undermentioned summer, new pools of asphalt signifier at the surface. Over 10s of 1000s of old ages, this rhythm produced the conic bone masses found at Rancho La Brea Fossil sedimentations range in size from a few pess to over 30 pess ( 10 metres ) deep.

Very few dodos of nocturnal animate beings have been found at Rancho La Brea. Why? Merely as the asphalt hardens during the cool winter months, so it besides hardens on cool darks.

Frequently the shallow pools of asphalt were hidden by a surface bed of fallen foliages and dust, and on occasion an unwary animate being wandered or was chased into the pool and became stuck. Here American king of beastss chase a bison calf. If the king of beastss chase the calf over a concealed asphalt sedimentation, they might go at bay.


Dodos are grounds of past life. They are formed in many ways. After a works or animate being dies, its soft tissues normally decay or are eaten. Most dodos are formed when the difficult parts are protected from decay by natural burial shortly after the being dies. For this ground, most dodos are found in deposits that were laid down by H2O – either ancient rivers, lakes, or oceans.

The Rancho La Brea dodos were preserved by a alone combination of deposit and asphalt impregnation. First the castanetss were saturated with asphalt, which inhibited decay. Preservation of the dodos took topographic point after the concentrated castanetss had been buried beneath water-borne deposit. Unlike most dodos, the dodos from Rancho La Brea are unchanged, original stuff.

This open sedimentation contains castanetss of many different types of animate beings. After all the castanetss from this sedimentation were carefully excavated, they were cleaned and taken to the Museum for survey. Some excavated castanetss are reassembled into skeletons for show.

Rancholabrean Phase

The Rancholabrean phase was a major division of Pleistocene clip and sedimentations in North America ( the Pleistocene era began about 1,600,000 old ages ago and ended approximately 10,000 old ages ago ) . The Rancholabrean phase follows the Irvingtonian and was named for the La Brea Tar Pits, Los Angeles, which are noted for their abundant remains of fossil animate beings. The Rancholabrean seemingly includes the span of clip covered by the Illinoian glacial phase, the undermentioned Sangamon interglacial phase, and the Wisconsin glacial phase, the last major glacial episode to impact North America.

The Rancholabrean zoology includes many modern signifiers, such as rotters, chiropterans, bison, gnawers, beavers ( including a elephantine signifier ) , bear, antelope, and cervid, every bit good as nonextant animate beings: mammoths, mastodons and saber-toothed cats. Farther South, tapirs, sloths, musk hogs, and armadillos were found. Rancholabrean zoologies are widely represented across the United States; many of the dodos found are in an first-class province of saving.

At the terminal of Rancholabrean times the mammal zoology of North America underwent a drastic decrease in Numberss and diverseness. This decrease may hold been connected with environmental alterations. It has been suggested that the reaching of worlds in North America was responsible for the widespread extinction. It seems improbable, nevertheless, that worlds were present in sufficient Numberss or had the engineering to do the extinction of all the animate beings in inquiry, but they may hold cover the concluding blow to organize already greatly reduced and vulnerable to his predation.


  • The George C. Page Museum of La Brea Discoveries
  • 5801 Wilshire Boulevard, Los Angeles, CA 90036, online at: hypertext transfer protocol: //
  • The Discovery Channel, online at: hypertext transfer protocol: //
  • Encyclopedia Britannica Rancholabrean Stage, online at: hypertext transfer protocol: //

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Geology Of La Brea Tar Pits. (2017, Jul 10). Retrieved from