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La Brea Tar Pits (or Rancho La Brea Tar Pits) are a famous cluster of tar pits located in Hancock Park in the urban heart of Los Angeles, California, United States. Asphalt (colloquially termed tar, which in Spanish is termed brea, see below) has seeped up from the ground in this area for tens of thousands of years, forming hundreds of sticky pools that trapped animals and plants which happened to enter. Over time, the asphalt fossilized the remains. The result is an incredibly rich collection of fossils dating from the last ice age. Work started in the early 20th century. In the 1940s and 1950s there was great public excitement over the dramatic mammal fossils recovered. By the 2000s, attention had shifted to microfossils, to fossilized insects and plants, and even to pollen grains. These fossils help define a picture of what is thought to be a cooler, moister climate present in the Los Angeles basin during the glacial age. The George C. Page Museum in Hancock Park, part of the Natural History Museum of Los Angeles County, presents these discoveries. Of more than a hundred pits, one (Pit 91) continues to be regularly excavated for two months each summer, under the watchful eyes of tourists.[1] The park's location in a major urban center, the history of dramatic discoveries, and excellent presentation in the Page Museum combine to make the La Brea Tar Pits a famous and accessible paleontological site.
Location and information of the pitsThe La Brea Tar Pits and Hancock Park are situated within urban Los Angeles, California, near the Miracle Mile district. La Brea Tar Pits are composed of a substance called Asphalt, which came out of the earth as oil. In Hancock Park, asphalt seeps up from underground. The asphalt is derived from petroleum deposits which originate from underground locations throughout the Los Angeles Basin. The asphalt reaches the surface at several locations in the park, forming pools. Methane gas also seeps up, causing bubbles which makes the asphalt appear to boil. Asphalt and methane also appear under surrounding buildings, requiring special operations to remove, lest it weaken the buildings' foundations. It was recently discovered that the bubbles are caused by hardy forms of bacteria embedded in the natural asphalt that are eating away at the petroleum and releasing methane; of the bacteria sampled so far, about 200 to 300 are previously unknown species.[2] This seepage has been happening for tens of thousands of years. From time to time, the asphalt would form a pool deep enough to trap animals, and the surface would be covered with layers of water, dust, and leaves. Animals would wander in, become trapped and eventually die. Predators would also enter to eat the trapped animals, and themselves become stuck. As the bones of the dead animals sink into the asphalt, it fossilizes them, turning them a dark brown or black color. Lighter fractions of petroleum evaporate from the asphalt, leaving a more solid substance which holds the bones. Apart from the dramatic fossils of large mammals, the asphalt also preserves very small "microfossils", wood and plant remnants, and even pollen grains. Radiometric dating of preserved wood and bones has given an age of 38,000 years for the oldest known material from the La Brea seeps, and they are still ensnaring organisms today. La Brea animals and plantsAmong the prehistoric species associated with the La Brea Tar Pits are mammoths, dire wolves, short-faced bears, ground sloths, and the state fossil of California, the saber-toothed cat, Smilodon californicus. Only one human has ever been found, a partial skeleton of a woman, dated at approximately 9,000 BP ([1]). Much of the early work in identifying species was performed in the early 20th century by John C. Merriam of the University of California. The park is known for producing myriad mammal fossils dating from the last ice age. While mammal fossils occupy significant interest, other fossils, including fossilized insects and plants, and even pollen grains, are also valued. These fossils help define a picture of what is thought to be a cooler, moister climate present in the Los Angeles basin during the glacial age. Among these fossils are microfossils. Microfossils are retrieved from a matrix of asphalt and sandy clay by washing with a solvent to remove the petroleum, then picking through the remains under a high-powered lens. La Brea may be the only excavation sites in the world where the predators found outnumber prey. The reason for this is unknown but one credited theory is that a large prey animal (say, a mastodon) would die naturally or accidentally become entrapped in a tar pit, attracting numerous predators across long distances. This so-called predator trap would kill many animals that found themselves stuck along with their prey. Another theory, specific to the Dire Wolf, suggests that both prey and predators may have been trapped accidentally during the hunt. Since wolves hunt in packs, each prey animal could take several wolves with it. MammalsBelow is a partial list of extinct and extant animals with their scientific names included on the right side. This is a selection from the complete catalogue. Herbivores
Carnivores
OmnivoresBirdsA partial list of extinct and extant birds found as fossils at La Brea. Reptiles, amphibians, and fish
ArthropodsPlantsFurther informationBrea is Spanish for "tar", making "The La Brea Tar Pits" a redundant expression meaning "The The Tar Tar Pits" (an example of pleonasm). The "tar" pits were used as a source of asphalt (for use as low-grade fuel and for waterproofing and insulation) by early settlers of the Los Angeles area. Early settlers mistook the bones in the pits for the remains of unlucky pronghorns or local cattle that had become mired. Rancho La Brea is the most famous, but there are two other asphalt pits with fossils in southern California: in Carpinteria, Santa Barbara County and McKittrick, in Kern County. There are other fossil-bearing asphalt deposits in Texas, Peru, Trinidad, Iran, Russia and Poland. For other rich deposits, fossilized where they occurred, see Lagerstätten. La Brea in fiction
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References
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