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| In 2007, researchers from ] discovered that the bubbles were caused by hardy forms of ] embedded in the natural asphalt. After consuming ], the bacteria release methane. Of the bacteria sampled so far, about 200 to 300 are previously unknown species.<ref name="LAT051407">Jia-Rui Chong, , ''Los Angeles Times'', May 14, 2007.</ref> | In 2007, researchers from ] discovered that the bubbles were caused by hardy forms of ] embedded in the natural asphalt. After consuming ], the bacteria release methane. Of the bacteria sampled so far, about 200 to 300 are previously unknown species.<ref name="LAT051407">Jia-Rui Chong, , ''Los Angeles Times'', May 14, 2007.</ref> | ||
| ===La Brea Woman Unveiled=== | |||
| In the summer of 2009, the only human ever found at the Tar Pits was finally given a face. She is know as the "La Brea Woman" and has been aged at about 9,000 years. Forensic Artist, Melissa Cooper, created the first 2-Dimensional facial reconstrucion based on her skull. A paper has been published in the 2010 winter issue of Prehistoric Times documenting the process. <ref name="Link to images of La Brea woman">{{cite web |url=http://www.mcforensicart.com/2d-reconstructions.html |title=La Brea Woman Skull Reconstruction</ref> | |||
| LA TImes has touched on this story as well mentioning the controversy behind it <ref name="Link to LA Times Article">{{cite web |url=http://latimesblogs.latimes.com/culturemonster/2009/11/the-skeleton-that-the-page-museum-doesnt-want-you-to-see.html |title=The Skeleton the Page Museum Doesn't Want You to See</ref> | |||
| ===George C. Page Museum=== | ===George C. Page Museum=== | ||
Revision as of 05:57, 18 January 2010
For the tar pit in La Brea, Trinidad and Tobago, see Pitch Lake.The La Brea Tar Pits (or Rancho La Brea Tar Pits) are a famous cluster of tar pits around which Hancock Park was formed, in the urban heart of Los Angeles. Asphalt or tar (brea in Spanish) has seeped up from the ground in this area for tens of thousands of years. The tar is often covered with water. Over many centuries, animals that came to drink the water fell in, sank in the tar, and were preserved as bones. The George C. Page Museum is dedicated to researching the tar pits and displaying specimens from the animals that died there.
Location and formation of the pits
The La Brea Tar Pits and Hancock Park are situated within urban Los Angeles, California, near the Miracle Mile district.
Tar pits are composed of heavy oil fractions called asphalt, which seeped from the earth as oil. In Hancock Park, crude oil seeps up along the 6th Street Fault from the Salt Lake Oil Field, which underlies much of the Fairfax District north of the park. The oil reaches the surface and forms pools at several locations in the park, becoming asphalt as the lighter fractions of the petroleum biodegrade.
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 to drink, become trapped, and eventually die. Predators would also enter to eat the trapped animals and become stuck.
As the bones of the dead animals sink into the asphalt, it soaks into 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, insects, dust, 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. They still ensnare organisms today.
Early history
The Portola expedition, a group of Mexican explorers led by Gaspar de Portola, made the first written record of the tar pits in 1769. Father Juan Crespi wrote, "While crossing the basin the scouts reported having seen some geysers of tar issuing from the ground like springs; it boils up molten, and the water runs to one side and the tar to the other. The scouts reported that they had come across many of these springs and had seen large swamps of them, enough, they said, to caulk many vessels. We were not so lucky ourselves as to see these tar geysers, much though we wished it; as it was some distance out of the way we were to take, the Governor did not want us to go past them. We christened them Los Volcanes de Brea ."
Scientific resource
Contemporary excavations of the bones started in the early 20th century. In the 1940s and 1950s, public excitement was generated over the recovery of dramatic large mammal bones. (The organic remains could be called "fossils" because they were dug up, but they were not mineralized like true fossils.)
By the 2000s, research attention had shifted to smaller specimens, such as preserved insects and plant parts, including microfossils, such as pollen grains. These remains have contributed to an understanding of the Los Angeles basin during the glacial age, with a cooler and moister climate.
Source of methane discovered
Methane gas also escapes, causing bubbles that make the asphalt appear to boil. Asphalt and methane appear under surrounding buildings, and require special operations for removal to prevent weakening building foundations.
In 2007, researchers from UC Riverside discovered that the bubbles were caused by hardy forms of bacteria embedded in the natural asphalt. After consuming petroleum, the bacteria release methane. Of the bacteria sampled so far, about 200 to 300 are previously unknown species.
George C. Page Museum
The George C. Page Museum,' part of the Natural History Museum of Los Angeles County, was built next to the tar pits in Hancock Park on Wilshire Boulevard. It tells the story of the tar pits and presents specimens from them. Visitors can walk around the park and see the tar pits. On the grounds of the park are life-sized models of prehistoric animals in or near the tar pits. Of more than a hundred pits, only Pit 91 is still regularly excavated by researchers. The museum encloses the pit and tourists can watch as it is excavated for two months each summer. Paleontologists supervise and direct the work of volunteers.
La Brea is a famous and accessible paleontological site because it is in a large city, with dramatic exhibits well presented at the Page Museum.
Excavation of newly uncovered pits announced in 2009
On February 18, 2009, George C. Page Museum formally announced the 2006 discovery of 16 fossil deposits which had been removed from the ground during the construction of an underground parking garage for the Los Angeles County Museum of Art next to the tar pits. Among the finds are bones of a saber-toothed cat, six dire wolves, bison, horses, a giant ground sloth, turtles, snails, clams, millipedes, fish, gophers, and an American lion. Also discovered is a near-intact mammoth skeleton, nicknamed Zed; the only pieces missing are a rear leg, a vertebra and the top of his skull, which was shaved off by construction equipment in preparation to build the parking structure.
These fossils were packaged at the construction site and removed to the museum so that construction could continue. Over twenty large accumulations of tar and specimens were taken to be separated. As work for the public transit Metro Purple Line is extended, museum researchers know that more tar pits will be uncovered, for example near the intersection of Wilshire and Curson.
La Brea animals and plants
Among 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 who was apparently a victim of a homicide based on skull crush evidence . John C. Merriam of the University of California led much of the early work in identifying species in the early 20th century.
The park is known for producing myriad mammal fossils dating from the last Ice Age. While mammal fossils generate 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 have been a cooler, moister climate 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.
Tar pits around the world are unusual in accumulating more predators than prey. The reason for this is unknown, but one theory is that a large prey animal (say, a mastodon) would die or become stuck in a tar pit, attracting predators across long distances. This predator trap would catch predators along with their prey. Another theory is that dire wolves and their prey may have been trapped during a hunt. Since modern wolves hunt in packs, each prey animal could take several wolves with it.
Mammals
Below 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. The dagger symbol "†" indicates an extinct species.
Herbivores
- †Imperial Mammoth (Mammuthus imperator)
- †Columbian Mammoth (Mammuthus columbi)
- †American Mastodon (Mammut americanum)
- †Harlan's Ground Sloth (Paramylodon harlani)
- †Jefferson’s Ground Sloth (Megalonyx jeffersoni)
- †Shasta Ground Sloth (Nothrotheriops shastensis)
- †Ancient Bison (Bison antiquus) ()
- †American Camel (Camelops hesterus)
- †Stilt-legged Llama (Hemiauchenia macrophala)
- †Western Horse (Equus "occidentalis")
- †Mexican Horse (Equus conversidens)
- †Peccary (Platygonus compressus)
- Pronghorn (Antilocapra americana)
- †Tar-pit pronghorn (Capromeryx minor)
- †California Tapir (Tapirus californicus)
- Elk (Wapiti) (Cervus canadensis)
- Deer (Odocoileus sp.)
Carnivores
- †Short-faced bear (Arctodus simus)
- Brown bear (Ursus arctos)
- Black bear (Ursus americanus)
- †American Lion (Panthera leo atrox)
- †Scimitar Cat (Homotherium serum)
- †Sabre-Toothed Cat (Smilodon fatalis)
- Jaguar (Panthera onca augusta)
- †American cheetah (Miracinonyx inexpectatus)
- Cougar (Puma concolor)
- †Dire Wolf (Canis dirus)
- Gray Wolf (Canis lupus)
- Coyote (Canis latrans)
- Bobcat (Lynx rufus)
- Weasel
Omnivores
Birds
A partial list of extinct and extant birds found as fossils at La Brea.
- California Condor
- Eagle
- Hawk
- Falcon
- †Teratorns
- Vulture
- †La Brea Caracara
- Sandhill Crane
- Canada Goose
- Mallard Duck
- Night Heron
- †La Brea Stork
- Grebe
- Cormorant
- Common Raven
- Magpie
- Horned Lark
- Shrike
- Common Poor-will
- Flicker
- Great Horned Owl
- †La Brea Owl
- Greater Roadrunner
- Mourning Dove
- Band-Tailed Pigeon
- Avocet
- Killdeer
- Curlew
- California Quail
- Turkey (†Californian Turkey)
Reptiles, amphibians, and fish
- Arroyo Chub
- Garter Snake
- Gopher Snake
- Kingsnake
- Pond Turtle
- Rainbow Trout
- Rattlesnake
- Salamander
- Three-spined stickleback
- Tree Frog
- Toad
Arthropods
Plants
- California Juniper
- Coast Live Oak
- Poison Oak
- Ragweed
- Raspberry
- Red Cedar
- Redwood tree
- Sagebrush
- California Sycamore
- Thistle
- Walnut tree
Further information
Brea 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. They mistook the bones in the pits for the remains of pronghorn antelope or 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.
See also
References
- Khilyuk, Leonid F. (2000). Gas migration: events preceding earthquakes. Gulf Professional Publishing. p. 280-282. ISBN 0884154300.
{{cite book}}: More than one of|pages=and|page=specified (help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - Kielbasa, John R. (1998), "Rancho La Brea", Historic Adobes of Los Angeles County, Pittsburg: Dorrance Publishing Co., ISBN 0-8059-4172-X.
- Jia-Rui Chong, "Researchers learn why tar pits are bubbly", Los Angeles Times, May 14, 2007.
- M. Albano, personal observation
- Page Museum. "Page Museum - La Brea Tar Pits". Page Museum web site. The Natural History Museum of Los Angeles County Foundation. Retrieved 2006-12-15.
- ^ "Cache Of Ice Age Fossils Found Near Tar Pits". Los Angeles: KCBS-TV. Associated Press. February 18, 2009. Retrieved February 18, 2009.
- ^ Thomas H. Maugh II (February 18, 2009). "Major cache of fossils unearthed in L.A." Los Angeles Times. Los Angeles. Retrieved February 18, 2009.
- "Workers Unearth Mammoth Discovery near La Brea Tar Pits". Los Angeles: KTLA. February 18, 2009. Retrieved February 18, 2009.
- "Nearly intact mammoth found at L.A. construction site". USA Today. February 18, 2009. Retrieved February 18, 2009.
- "Tar pits still slowly releasing victims"
- "La Brea Tar Pits Facility Will Celebrate 10th Anniversary", Los Angeles Times
External links
- Page Museum - La Brea Tar Pits
- UCMP Berkeley website describes the geology and paleontology of the asphalt seeps.
- Setting the La Brea site in context.
- La Brea Tar Pits Visitor Guide
34°03′46″N 118°21′22″W / 34.062828°N 118.355992°W / 34.062828; -118.355992
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