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The hour hand on a clock moves about ten thousand times faster than the "flowing" rocks of the mantle.
鐘面上時針的移動速度，比地幔巖石的“流動”速度，要快大約1萬倍。
The movements occur not just laterally as the Earth's plates move across the surface, but up and down as well, as rocks rise and fall under the churning process known as convection. Convection as a process was first deduced by the eccentric Count von Rumford at the end of the eighteenth century. Sixty years later an English vicar named Osmond Fisher presciently suggested that the Earth's interior might well be fluid enough for the contents to move about, but that idea took a very long time to gain support.
移動不僅真的發(fā)生，就像地球的板塊做平面移動那樣，而且還上下移動，就像巖石在所謂對流的攪動作用之下時起時伏。對流作為一種過程是倫福德伯爵在18世紀末首先推斷出來的。60年以后，一位名叫奧斯蒙·費希爾的英國牧師很有先見之明地提出，地球內(nèi)部可能是液態(tài)的，東西可以在上面自由移動，但那種見解過了很久才獲得別人的支持。
In about 1970, when geophysicists realized just how much turmoil was going on down there, it came as a considerable shock. As Shawna Vogel put it in the book Naked Earth: The New Geophysics: "It was as if scientists had spent decades figuring out the layers of the Earth's atmosphere—troposphere, stratosphere, and so forth—and then had suddenly found out about wind."
大約1970年，當?shù)刭|(zhì)學家們意識到地底下簡直亂成一鍋粥的時候，這個消息還真讓人嚇一大跳。肖納·沃格爾在他的《赤裸裸的地球：新地球物理學》一書中說：“這就好比科學家們花了幾十年時間才發(fā)現(xiàn)地球大氣的層次——對流層、平流層等等，然后突然之間發(fā)現(xiàn)了風。”
How deep the convection process goes has been a matter of controversy ever since. Some say it begins four hundred miles down, others two thousand miles below us. The problem, as Donald Trefil has observed, is that "there are two sets of data, from two different disciplines, that cannot be reconciled." Geochemists say that certain elements on Earth's surface cannot have come from the upper mantle, but must have come from deeper within the Earth. Therefore the materials in the upper and lower mantle must at least occasionally mix. Seismologists insist that there is no evidence to support such a thesis.
自那以來，對流過程到底有多深一直成了個爭論不休的問題。有的說它始于650公里下面，有的說是3000多公里下面。詹姆斯·特雷菲爾認為，問題在于“來自兩個不同學科的兩套數(shù)據(jù)，二者是不可調(diào)和的”。地球化學家們說，地球表面的某些元素不可能來自上層地幔，肯定來自地球內(nèi)部更深的地方。因此，上層地幔和下層地幔的物質(zhì)至少是偶爾相混的。地震學家認為，沒有證據(jù)支持這樣的論點。
