VOA慢速英语:Archeological Dig Area in the American State of South Carolina Continues To Surrender Secret

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This is SCIENCE IN THE NEWS in VOA Special English. I'm Bob Doughty.

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And I'm Barbara Klein. On our program this week, we will tell about the mystery of the aurora borealis, better known as the Northern Lights. We will also tell about an archeological dig in the southeastern United States. The project continues to surrender secrets of some very early Americans.

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For many centuries, people have looked with wonder at the Northern Lights. These mysterious lights often brighten the night sky in countries near the North Pole. The Northern Lights are also called the aurora borealis. An aurora is a natural burst of light that can be seen with the unaided eye. An aurora over the South Pole is called the aurora australis, or Southern Lights.

Auroras appear as large areas of moving light. They are often green, red or purple in color. Some auroras can extend across the sky for thousands of kilometers.

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Scientists have long known that auroras are caused by a storm of magnetic energy high above the Earth's surface. But scientists have been debating exactly what forces in nature cause these storms to create the colorful lightshows.

Recently, researchers working for the American space agency said they found the answer by using five of the agency's satellites. The researchers say the Sun's and Earth's electromagnetic fields normally move past one another in different directions. But when enough energy builds between the two fields, they separate and reconnect themselves in a new shape.

This reconnection releases a huge amount of electrical current in the Earth's magnetosphere. The researchers say the reconnection happens about one hundred twenty-nine kilometers away from the planet. That is about one third of the distance to the moon.

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The five satellites were launched last year as part of the American space agency's THEMIS project. THEMIS is a word the agency uses to represent Time History of Events and Macroscale Interactions During Substorms.

The researchers were able to directly observe the magnetic substorms using both the satellites and twenty ground observatories. The observatories are in Canada and the American state of Alaska.

Every four days, the satellites lined up half way between the North and South Poles to record observations. Equipment on the ground helped to identify when and where a substorm was forming. Other devices measure the auroral light from particles moving along Earth's magnetic field. Their observations of six months ago confirmed that magnetic reconnection leads to substorms.

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The researchers say there is still more to be discovered about substorms. The Northern Lights are exciting to watch. However, the forces responsible for them can damage satellites, guidance systems and radio communication. They are also a possible threat to air travelers and astronauts.

Scientists hope that more investigation will lead to better methods of predicting substorms, both to protect equipment and lives.

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You are listening to the VOA Special English program SCIENCE IN THE NEWS. With Barbara Klein, I'm Bob Doughty.

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A college student recently found two ancient stone objects in the American state of South Carolina. He made the discovery during an archeological dig in an area known as the Topper Site.

The student, Matthew Carey, found the objects just a short distance from each other. They appear to have been buried together. University of South Carolina archeologist Albert Goodyear said the objects could be cutting tools. But he believes they look like the heads of spears or long knives. Mister Goodyear said they seem to be about eleven thousand years old.

Earlier archeological work at the Topper Site may have uncovered evidence of a settlement from as early as fifty thousand years ago.

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The Topper Site got its name from a local man. Years ago, David Topper told Mister Goodyear about a place he might find interesting near the Savannah River. A chemical company owns the land. The company lets the scientists work on the huge site each spring. The Topper Site covers an area measuring more than thirty thousand square meters.

Digging begins when the local wild-turkey-hunting season ends. Each May, Albert Goodyear leads volunteers for five weeks in uncovering the site's mysteries. The volunteers are scientists, teachers, students, and anyone else who likes to explore the past. They dig by hand. It is hard, painstaking work. But most scientists would say the site is well worth the hard work it requires.

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Mister Goodyear first began working near the place that would become the Topper Site in the nineteen eighties. He led a team searching for objects belonging to the Clovis people. Most scientists at the time believed that these people were the first settlers in the Americas.

The name "Clovis" came from an area near Clovis, New Mexico. Evidence of the people was found there. Scientists had long believed that human beings first entered North America across a land bridge from what is now Russia and Alaska. They thought these first Americans arrived about eleven or twelve thousand years ago. But in the late twentieth century, some researchers began to question that theory.

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Several discoveries became especially important in disputing the belief. Among the most important ones were findings at the Monte Verde Camp in Chile. Scientists began finding ancient artifacts there beginning in nineteen seventy-six. The artifacts included a piece of meat that had lasted many centuries. It might have been from an ancient animal similar to a modern elephant.

The findings at Monte Verde showed that humans were in South America about thirteen thousand years ago. Experts said that was about one thousand years before the Clovis people could have traveled there.

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In nineteen ninety-eight, Mister Goodyear and his team wanted to find more artifacts of the Clovis people. He planned a dig near the Savannah River. But the river had flooded the area he wanted to examine. So he decided to start digging nearby.

Today, he remembers how much he regretted the flood. He told V.O.A. that did not want to move his explorations. But the area proved a big surprise. The archeologist described it as the best thing that ever happened to him.

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The flood caused Mister Goodyear and his team to dig about a meter deeper than usual for Clovis artifacts. They found evidence of tools and extremely small stone particles or flakes. The objects appeared older than those made or used by the Clovis people. The objects were found during the last two weeks of the Goodyear team's yearly research project.

Digging at Topper in the following years added to the artifact collection. The scientists found artifacts that appear to have come from times before the Clovis people.

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Four years ago, Mister Goodyear and his team found ancient plant material at the Topper Site. Shortly before the work was to end, they discovered black soil. The soil provided charcoal, a material combining wood and other substances. Charcoal can be tested for age by a process called radiocarbon dating.

Tom Stafford of the Stafford Research Laboratories in Colorado arrived to take pieces of the charcoal. Months later, the test results were announced. They showed that the charcoal could be up to fifty thousand years old.

If correct, it would mean that the first settlement in the Americas took place many years earlier than had been thought. It could also mean settlers lived in North America fifty thousand years ago.

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Some experts do not accept that human beings made or used the most ancient objects found at the Topper Site. Some believe that the weather and the ages made these artifacts look like tools. And experts continue to disagree about when North America was settled.

Mister Goodyear and his team plan to continue digging. They hope to find more evidence of very early peoples in America. When next May comes, they will be again excavating at the Topper Site.

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This SCIENCE IN THE NEWS program was written by Jerilyn Watson and Brianna Blake, who also was our producer. I'm Bob Doughty.

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And I'm Barbara Klein. You can read and listen to our programs at VOAspecialenglish.com. Join us next week for more news about science in VOA Special English.