【2017年整理】GMAT阅读解析每周一篇-by 申友Alice.docVIP

Scientists generally credit（把什么归因于，表示因果关系）violent collisions between tectonic plates, the mobile fragments of Earth’s rocky outer shell（插入语解释说明，略读）, with sculpting the planet’s surface, as, for example, when what is now the Indian subcontinent collided with Asia, producing the Himalayan Mountains.（举例喜马拉雅山形成具体解释了板块构造学说）However, plate tectonics cannot fully explain certain massive surface features, such as the “superswell” of southern Africa, a vast plateau over 1,000 miles across and nearly a mile high（同位语，解释superswell，略读）. Geologic evidence shows that southern African has been slowly rising for the past 100 million years, yet it has not experienced a tectonic collision for nearly 400 million years. // 科学家用板块构造学说来解释地表的形成，但有些大规模的地表特征，如南非的超级海隆却无法用板块学说来充分地解释。 The explanation may be in Earth’s mantle, the layer of rock underlying the tectonic plates and extending down over 1,800 miles to the outer edge of Earth’s iron core（一般自然科学题材中的重点专业词汇文中会给出解释，比如此处用同位语解释说明Earth’s mantle）. Since the early twentieth century, geophysicists have understood that the mantle churns and roils like a thick soup. The relative low density of the hottest rock makes that material buoyant, so it slowly ascends, while cooler, denser rock sinks until heat escaping the molten core warms it enough to make it rise again. While this process of convection was known to enable the horizontal movement of tectonic plates, until recently geophysicists were skeptical of its ability to lift or lower the planet’s surface vertically.// 解释了地幔，并说明对流主要作用于水平运用，最近地球物理学家怀疑其是否可以作用于垂直方向。 However, recent technological advances have allowed geophysicists to make three-dimensional “snapshots” of the mantle by measuring vibrations, or seismic waves, set in motion by earthquakes originating in the planet’s outer shell and recording the time it takes for them to travel from an earthquake’s epicenter to a particular recording station at the surface. Because geophysicists know that seismic waves become sluggish in hot, low-den