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Earth"s Inner CoreScientists have long struggled to understand what lies at the planet"s center. Direct observation of its center is impossible, so researchers must 1 to other evidence.In 1889, a German scientist detected a severe earthquake in Japan. Geophysicists concluded that shock waves 2 jolts (晃动) from one side of Earth through the center to the other side. Then in 1936, Danish geophysicist lnge Lehmann studied the waves" 3 to determine that within Earth"s core of molten (熔化了的) iron lies a solid inner core—but 4 that core was made of eluded (难倒) her. Other geophysicists quickly determined that Lehmann"s inner core was composed mostly 5 iron. Since then, Lehmann"s discovery has 6 conventional Earth science.But now scientists are challenging traditional theory with new and radical 7 . For example, Earth"s center could actually contain an "inner core within the inner core", claim Ishii and colleague Adam Dziewonski.Analyzing hundreds of thousands of earthquake wave 8 , they maintain that the inner core has at its heart a tiny, even more solid sphere (球体). This sphere "may be the oldest fossil 9 from the formation of Earth," says Dziewonski.Dziewonski and Ishii speculate that shortly 10 Earth formed around 4.8 billion years ago, a giant asteroid (小行星) smashed into the young planet and nearly melted it. But Earth"s center didn"t quite melt; it 11 mass as the planet cooled. The core within a core may be the kernel (核心) that endured. "Its presence could change our basic ideas about the 12 of the planet," Dziewonski says.Dziewonski"s idea is tame (温和的) compared to the 13 theories of independent geophysicist J. Marvin Herndon. Earth"s inner core is made not of iron, he claims, but a 14 of nickel and silicon. Herndon has a truly revolutionary notion: Within the nickel silicide (硅化物) inner core is also an "inner" inner core—an 8 km-wide ball of the element uranium. Uranium is radioactive. Herndon thinks the uranium releases heat energy as its atoms 15 fission-split and crash into one another in a chain reaction. In other words, we may live on top of a gigantic, "natural" nuclear power plant.
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Earth"s Inner CoreScientists have long struggled to understand what lies at the planet"s center. Direct observation of its center is impossible, so researchers must 1 to other evidence.In 1889, a German scientist detected a severe earthquake in Japan. Geophysicists concluded that shock waves 2 jolts (晃动) from one side of Earth through the center to the other side. Then in 1936, Danish geophysicist lnge Lehmann studied the waves" 3 to determine that within Earth"s core of molten (熔化了的) iron lies a solid inner core—but 4 that core was made of eluded (难倒) her. Other geophysicists quickly determined that Lehmann"s inner core was composed mostly 5 iron. Since then, Lehmann"s discovery has 6 conventional Earth science.But now scientists are challenging traditional theory with new and radical 7 . For example, Earth"s center could actually contain an "inner core within the inner core", claim Ishii and colleague Adam Dziewonski.Analyzing hundreds of thousands of earthquake wave 8 , they maintain that the inner core has at its heart a tiny, even more solid sphere (球体). This sphere "may be the oldest fossil 9 from the formation of Earth," says Dziewonski.Dziewonski and Ishii speculate that shortly 10 Earth formed around 4.8 billion years ago, a giant asteroid (小行星) smashed into the young planet and nearly melted it. But Earth"s center didn"t quite melt; it 11 mass as the planet cooled. The core within a core may be the kernel (核心) that endured. "Its presence could change our basic ideas about the 12 of the planet," Dziewonski says.Dziewonski"s idea is tame (温和的) compared to the 13 theories of independent geophysicist J. Marvin Herndon. Earth"s inner core is made not of iron, he claims, but a 14 of nickel and silicon. Herndon has a truly revolutionary notion: Within the nickel silicide (硅化物) inner core is also an "inner" inner core—an 8 km-wide ball of the element uranium. Uranium is radioactive. Herndon thinks the uranium releases heat energy as its atoms 15 fission-split and crash into one another in a chain reaction. In other words, we may live on top of a gigantic, "natural" nuclear power plant.
Earth"s Inner CoreScientists have long struggled to understand what lies at the planet"s center. Direct observation of its center is impossible, so researchers must 1 to other evidence.In 1889, a German scientist detected a severe earthquake in Japan. Geophysicists concluded that shock waves 2 jolts (晃动) from one side of Earth through the center to the other side. Then in 1936, Danish geophysicist lnge Lehmann studied the waves" 3 to determine that within Earth"s core of molten (熔化了的) iron lies a solid inner core—but 4 that core was made of eluded (难倒) her. Other geophysicists quickly determined that Lehmann"s inner core was composed mostly 5 iron. Since then, Lehmann"s discovery has 6 conventional Earth science.But now scientists are challenging traditional theory with new and radical 7 . For example, Earth"s center could actually contain an "inner core within the inner core", claim Ishii and colleague Adam Dziewonski.Analyzing hundreds of thousands of earthquake wave 8 , they maintain that the inner core has at its heart a tiny, even more solid sphere (球体). This sphere "may be the oldest fossil 9 from the formation of Earth," says Dziewonski.Dziewonski and Ishii speculate that shortly 10 Earth formed around 4.8 billion years ago, a giant asteroid (小行星) smashed into the young planet and nearly melted it. But Earth"s center didn"t quite melt; it 11 mass as the planet cooled. The core within a core may be the kernel (核心) that endured. "Its presence could change our basic ideas about the 12 of the planet," Dziewonski says.Dziewonski"s idea is tame (温和的) compared to the 13 theories of independent geophysicist J. Marvin Herndon. Earth"s inner core is made not of iron, he claims, but a 14 of nickel and silicon. Herndon has a truly revolutionary notion: Within the nickel silicide (硅化物) inner core is also an "inner" inner core—an 8 km-wide ball of the element uranium. Uranium is radioactive. Herndon thinks the uranium releases heat energy as its atoms 15 fission-split and crash into one another in a chain reaction. In other words, we may live on top of a gigantic, "natural" nuclear power plant.
Earth"s Inner CoreScientists have long struggled to understand what lies at the planet"s center. Direct observation of its center is impossible, so researchers must 1 to other evidence.In 1889, a German scientist detected a severe earthquake in Japan. Geophysicists concluded that shock waves 2 jolts (晃动) from one side of Earth through the center to the other side. Then in 1936, Danish geophysicist lnge Lehmann studied the waves" 3 to determine that within Earth"s core of molten (熔化了的) iron lies a solid inner core—but 4 that core was made of eluded (难倒) her. Other geophysicists quickly determined that Lehmann"s inner core was composed mostly 5 iron. Since then, Lehmann"s discovery has 6 conventional Earth science.But now scientists are challenging traditional theory with new and radical 7 . For example, Earth"s center could actually contain an "inner core within the inner core", claim Ishii and colleague Adam Dziewonski.Analyzing hundreds of thousands of earthquake wave 8 , they maintain that the inner core has at its heart a tiny, even more solid sphere (球体). This sphere "may be the oldest fossil 9 from the formation of Earth," says Dziewonski.Dziewonski and Ishii speculate that shortly 10 Earth formed around 4.8 billion years ago, a giant asteroid (小行星) smashed into the young planet and nearly melted it. But Earth"s center didn"t quite melt; it 11 mass as the planet cooled. The core within a core may be the kernel (核心) that endured. "Its presence could change our basic ideas about the 12 of the planet," Dziewonski says.Dziewonski"s idea is tame (温和的) compared to the 13 theories of independent geophysicist J. Marvin Herndon. Earth"s inner core is made not of iron, he claims, but a 14 of nickel and silicon. Herndon has a truly revolutionary notion: Within the nickel silicide (硅化物) inner core is also an "inner" inner core—an 8 km-wide ball of the element uranium. Uranium is radioactive. Herndon thinks the uranium releases heat energy as its atoms 15 fission-split and crash into one another in a chain reaction. In other words, we may live on top of a gigantic, "natural" nuclear power plant.
The Exploding Lakes of CameroonWhat comes to mind when you think of a lake You probably imagine a pretty scene with blue water, birds, and fish. For the people in the northwestern Cameroon, however, the image is very different. For them, lakes may mean terrible disasters. In 1984, poisonous gases exploded out of Lake Monoun and came down into the nearby villages, killing thirty-seven people. Two years later, Lake Nyos erupted. A cloud of gases rolled down the hills and into the valleys and killed 1,700 people.Lake Nyos and Lake Monoun are crater (火山口) lakes. They were formed when water collected in the craters of old volcanoes. The volcanoes under Lake Nyos and Lake Monoun are not active anymore. However, poisonous gases from the center of the earth continue to flow up through cracks in the bottom of the lake. This is normal in a crater lake. In most crater lakes, these gases are released often because the water "turns over" regularly. That is, the water from the bottom of the lake rises and mixes with the water at the top, allowing the gases to escape slowly.However, in Lakes Nyos and Monoun, there is no regular turning over. No one knows the reason for this fact, but as a result, these lakes have more gases trapped at the bottom than other crater lakes. In fact, scientists who have studied Lakes Nyos and Monoun have found 16,000 times more gases. When a strong wind, cool weather, a storm, or a landslide (滑坡) causes the water to turn over suddenly, the gases escape in a violent explosion.In the past, no one knew when the gases might explode, so there was no way for the villagers to escape disaster. Now scientists from the United States, France, and Cameroon have found a way to reduce the gas pressure at the bottom of Lake Nyos. They stood a 672-foot plastic pipe in the middle of the lake, with one end of the pipe near the bottom and the other end in the air. Near the top of the pipe, the team put several holes that could be opened or closed by a computer. Now, when the gas pressure gets too high, the holes are opened and some of the gas-filled water shoots up through the pipe into the air like a fountain. With less pressure, a disastrous explosion is much less likely. However, the scientists are not sure that one pipe will be enough to prevent explosions. They hope to put in others soon and they plan to install a similar pipe and a computer system at Lake Monoun as well.To protect people nearby until all of the pipes are in place, the scientists have installed early warning systems at both lakes. If the gas pressure rises to a dangerous level, computers will set off loud sirens (警报) and bright lights to warn the people in the villages. That way, they will have time to escape from the dangerous gases. A team of scientists has
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