Passage6
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 itslowly 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 geophysicistswere skeptical ofits 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-density rock, and speed up in colder, denser regions, they can now infer the temperatures and densities in a given segment of the interior. By compiling a map of seismic velocities from thousands of earthquakes across the globe, they can also begin to map temperatures and densities throughout the mantle.//现在科技发达可以探测震波、时间、速度等因素，以此可以推测出各个部分内部的温度和密度。These methods have revealed some unexpectedly immense formations in the deepest parts of the mantle; the largest of these is a buoyant mass of hot rock directly below Africa’s southern tip. Dispelling researchers’ initial doubts, computer models have confirmed that this formation is buoyant enough to rise slowly within the mantle and strong enough to push Africa upward as it rises. //现在科技探测到南非的板块下有大量活跃的热岩石，活跃的程度可以使非洲陆地上升。
逻辑简图：自然科学题材的一段式文章 现象解释的写作结构
第一层：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。
第二层：解释了地幔，岩石热、密度小时会上升，岩石冷、密度小时会下降，说明对流主要作用于水平方向，最近地球物理学家怀疑其是否可以作用于垂直方向。
第三层：现在科技发达可以探测震波、时间、速度等因素，以此可以推测出各个部分内部的温度和密度。
第四层：现在科技探测到南非的板块下有大量活跃的热岩石，活跃的程度可以使非洲陆地上升。
1. The passage is primarily concerned with （主旨题，文章的主要内容是提出一个自然现象，然后通过现代进步的科技手段来分析解释这个现象。）
A. describing a tradit
