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The hour hand on a clock moves about ten thousand times faster than the "flowing" rocks of the mantle.
钟面上时针的移动速度，比地幔岩石的“流动”速度，要快大约1万倍。
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.
移动不仅真的发生，就像地球的板块做平面移动那样，而且还上下移动，就像岩石在所谓对流的搅动作用之下时起时伏。对流作为一种过程是伦福德伯爵在18世纪末首先推断出来的。60年以后，一位名叫奥斯蒙·费希尔的英国牧师很有先见之明地提出，地球内部可能是液态的，东西可以在上面自由移动，但那种见解过了很久才获得别人的支持。
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."
大约1970年，当地质学家们意识到地底下简直乱成一锅粥的时候，这个消息还真让人吓一大跳。肖纳·沃格尔在他的《赤裸裸的地球：新地球物理学》一书中说：“这就好比科学家们花了几十年时间才发现地球大气的层次——对流层、平流层等等，然后突然之间发现了风。”
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.
自那以来，对流过程到底有多深一直成了个争论不休的问题。有的说它始于650公里下面，有的说是3000多公里下面。詹姆斯·特雷菲尔认为，问题在于“来自两个不同学科的两套数据，二者是不可调和的”。地球化学家们说，地球表面的某些元素不可能来自上层地幔，肯定来自地球内部更深的地方。因此，上层地幔和下层地幔的物质至少是偶尔相混的。地震学家认为，没有证据支持这样的论点。
