Thursday, April 8, 2010
Los Angeles' La Brea Tar Pits: Ancient Animals, from VOA.
BOB DOUGHTY: I'm Bob Doughty.
FAITH LAPIDUS: And I'm Faith Lapidus with EXPLORATIONS in VOA Special English. Today we tell about a scientific research area in the United States. It is filled with the remains of ancient animals. This unusual place is in the center of Los Angeles, California. Its name is Rancho La Brea. But most people know it as the La Brea Tar Pits.
BOB DOUGHTY: To understand why La Brea is an important scientific research center we must travel back through time almost forty thousand years. Picture an area that is almost desert land. The sun is hot. A pig-like creature searches for food. It uses its short, flat nose to dig near a small tree. It finds nothing. The pig starts to walk away, but it cannot move its feet.
They are covered with a thick, black substance. The more it struggles against the black substance, the deeper it sinks. It now screams in fear and fights wildly to get loose.
Less than a kilometer away, a huge cat-like creature with two long front teeth hears the screams. It, too, is hungry. Traveling across the ground at great speed, the cat nears the area where the pig is fighting for its life.
The cat jumps on the pig and kills it. The pig dies quickly, and the cat begins to eat. When it attempts to leave, the cat finds it cannot move. The more the big cat struggles, the deeper it sinks into the black substance.
Before morning, the cat is dead. Its body, and the bones of the pig, slowly sink into the sticky black hole.
FAITH LAPIDUS: Scientists say the story we have told you happened again and again over a period of many thousands of years. The black substance that trapped the animals came out of the Earth as oil.
The oil dried, leaving behind a partly solid substance called asphalt. In the heat of the sun, the asphalt softened. Whatever touched it would often become trapped forever.
In seventeen sixty-nine, a group of Spanish explorers visited the area. They were led by Gaspar de Portola, governor of Lower California.
The group stopped to examine the sticky black substance that covered the Earth. They called the area “La Brea,” the Spanish words for “the tar.”
Many years later, settlers used the tar, or asphalt, on the tops of their houses to keep water out. They found animal bones in the asphalt, but threw them away. In nineteen-oh-six, scientists began to study the bones found in La Brea. Ten years later, the owner of the land, George Allan Hancock, gave it to the government of Los Angeles. His gift carried one condition. He said La Brea could only be used for scientific work.
BOB DOUGHTY: Today, the La Brea Tar Pits are known to scientists around the world. The area is considered one of the richest areas of fossil bones in the world. It is an extremely valuable place to study ancient animals. Scientists have recovered more than one million fossil bones from the La Brea Tar Pits. They have identified more than six hundred different kinds of animals and plants.
The fossils are from creatures as small as insects to those that were bigger than a modern elephant. These creatures became trapped as long ago as forty thousand years. It is still happening today. Small birds and animals still become trapped in the La Brea Tar Pits.
FAITH LAPIDUS: Rancho La Brea is the home of a modern research center and museum. Visitors can see the ancient fossil bones of creatures like the imperial mammoth and the American mastodon. Both look something like the modern day elephant, but bigger.
The museum also has many fossil remains of the huge cats that once lived in the area. They are called saber-toothed cats because of their long, fierce teeth. Scientists have found more than two thousand examples of the huge cats.
The museum also has thousands of fossil remains of an ancient kind of wolf. Scientists believe large groups of wolves became stuck when they came to feed on animals already trapped in the asphalt.
BOB DOUGHTY: In nineteen sixty-nine, scientists began digging at one area of La Brea called Pit Ninety-One. They have found more than forty thousand fossils in Pit Ninety-One. More than ninety-five percent of the mammal bones are from just seven different animals. Three were plant-eaters. They were the western horse, the ancient bison and a two-meter tall animal called the Harlan’s ground sloth.
Four of the animals were meat-eating hunters. These were the saber-tooth cat, the North American lion, the dire wolf and the coyote. All these animals, except the dog-like coyote, have disappeared from the Earth.
FAITH LAPIDUS: Researchers say ninety percent of the fossils found are those of meat-eating animals. They say this is a surprise because there have always been more plant-eaters in the world. The researchers say each plant-eater that became trapped caused many meat-eaters to come to the place to feed. They, too, became trapped.
Rancho La Brea has also been a trap for many different kinds of insects. Scientists free these dead insects by washing the asphalt away with special chemicals. The La Brea insects give scientists a close look at the history of insects in southern California.
The La Brea Tar Pits have also provided science with interesting information about the plants that grew in the area. For many thousands of years, plant seeds landed in the sticky asphalt. The seeds have been saved for research. Scientists also have found pollen from many different kinds of plants.
The seeds and pollen, or the lack of them, can show severe weather changes over thousands of years. Scientists say these provide information that has helped them understand the history of the environment. The seeds and pollen have left a forty-thousand-year record of the environment and weather for this area of California.
BOB DOUGHTY: Digging at Pit Ninety-One was recently suspended in order to pay closer to attention to a new discovery called Project Twenty-Three. In two thousand six a nearby art museum began an underground building project.
La Brea scientists had a chance to investigate an area that otherwise would have been impossible to study. This area turned out to be very rich in fossils. So, twenty-three huge containers of tar, clay and mud were removed from the area for research. This is why the project is now known as Project Twenty-Three.
Scientists have fully examined only several boxes of earth and tar. It will take years to complete all of the containers. But scientists have so far counted over seven hundred parts from different organisms. One huge discovery was the nearly complete skeleton of a male mammoth. Researchers have named the mammoth Zed. This is the largest mammoth ever found in the area.
Rancho La Brea scientists publish an Internet blog that documents this exciting project. It describes in detail the huge amount of work involved in carefully examining the many layers of tar and earth. For example, you can learn about the degreasing machine. Researchers place a big block of tar into the machine. It removes the oily material, leaving behind hundreds of fossils.
FAITH LAPIDUS: Each year, thousands of visitors come to see the fossils at Rancho La Brea. They visit the George C. Page Museum. Mister Page was a wealthy man who became very interested in the scientific work being done at the tar pits. He gave the money to build the museum and research center.
Visitors to the museum can see the “fish bowl,” a laboratory surrounded by glass. Here, they can watch scientists do their research. Visitors can watch the scientists clean, examine, repair and identify fossils that are still being discovered. Through this process, scientists are able to answer questions and solve puzzles about animals and their environment from thousands of years ago. The objects found in Project Twenty-three could double the size of the research center’s collection.
It is exciting to stand only a few meters away and watch scientists clean the asphalt off a fossil that is thousands of years old. Visitors quickly learn why researchers consider Rancho La Brea a very special place.
BOB DOUGHTY: This program was written and produced by Dana Demange. I'm Bob Doughty.
FAITH LAPIDUS: And I'm Faith Lapidus. You can find a link to the La Brea Tar Pits blog on our Web site, voaspecialenglish.com. You can also comment on our programs. Join us again next week for EXPLORATIONS in VOA Special English.