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托福听力练习-科学美国人60秒:地球金矿

2017-04-20 17:37:37来源：科学美国人60秒

点击查看>>科学美国人60秒音频：地球金矿

　　科学美国人60秒听力练习：地球金矿

　　科学美国人60秒英文文本

　　凯伦·霍普金(Karen Hopkin)在报告中指出：不同年代岩石中的同位素揭示了地幔中的金矿是在地球形成之后，由陨石带到地球所形成的。

　　Thar’s gold in them thar hills—and we may have meteorites to thank. Because it appears that a rain of meteors nearly 4 billion years ago peppered the Earth’s exterior with precious metals. So says a study in the journal Nature. [Matthias Willbold, Tim Elliott and Stephen Moorbath, "The tungsten isotopic composition of the Earth’s mantle before the terminal bombardment"]

　　When Earth was forming, molten iron sank to its center, creating the planet’s core. That iron carried with it a slew of iron-loving metals, including gold and platinum. In fact, the Earth’s core is packed with enough precious metals to cover the entire planet four meters deep.

　　But not all that glitters is down at the planet’s center. Today there’s enough gold in the Earth’s rocky shell to please prospectors—and to puzzle planetary scientists: why is that gold not down in the core, too?

　　The answer, it seems, is that it wasn’t even on the Earth until after the core formed. Isotope concentrations in rock samples of different ages indicate that the composition of the Earth’s mantle changed after the planet was blasted with meteors 3.9 billion years ago. That bombardment coated our home with a thin veneer of riches. Which means that the gold in them thar hills is older than the hills.

　　—Karen Hopkin

　　中文翻译请点击下一页

本文关键字: 托福听力 科学美国人60秒

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