2014年12月13日托福考试听力真题解析

　　Convective mantle and radioactivity

　　In 1892, Thomson had been made Lord Kelvin in appreciation of his many scientific accomplishments. Kelvin calculated the age of Earth by using thermal gradients, and arrived at an estimate of 100 million years old.[20] He did not realize that Earth has a highly viscous fluid mantle, and this invalidated his estimate. In 1895, John Perry produced an age-of-Earth estimate of 2 to 3 billion years using a model of a convective mantle and thin crust.[20] Kelvin stuck by his estimate of 100 million years, and later reduced it to about 20 million years.

　　The discovery of radioactivity introduced another factor in the calculation. After Henri Becquerel's initial discovery in 1896, Marie and Pierre Curie discovered the radioactive elements polonium and radium in 1898; and in 1903, Pierre Curie and Albert Laborde announced that radium produces enough heat to melt its own weight in ice in less than an hour. Geologists quickly realized that this upset the assumptions underlying most calculations of the age of Earth. These had assumed that the original heat of the Earth and Sun had dissipated steadily into space, but radioactive decay meant that this heat had been continually replenished. George Darwin and John Joly were the first to point this out, in 1903.[21]

　　Conversation 2

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　　-TPO部分对应参考 (生活场景话题TPO5-C1/TPO8 –C1/TPO19-C2)

　　-TPO对应词汇

　　上瘾 be addicted to, 戒掉 be off 喝清咖啡 drink it black

　　咖啡因 caffeine style 正装formal suit, 休闲装casual jeans.

　　color 蓝色最好，navy(blue), solid blue, deep/light blue

　　褪色 fade,fain,lose the color 不褪色retain its color

　　size: 松loose, 紧tight, It's tight on waist. 缩水shrink

　　design: 条stripped, 点dotted, 格plaid, 做工精细 elegant, 短裤 shorts

　　各种运动 beach/gym activities, 冰球 ice hockey, 棒球 baseball,