EARTH – aeas精读训练 (10-12年级)
The geology of the Earth’s surface is dominated by the particular properties of water. Present on Earth in solid, liquid, and gaseous states, water is exceptionally reactive. It dissolves, transports, and precipitates many chemical compounds and is constantly modifying the face of the Earth.
Evaporated from the oceans, water vapor forms clouds, some of which are transported by wind over the continents. Condensation from the clouds provides the essential agent of continental erosion: rain. Precipitated onto the ground, the water trickles down to form brooks, streams, and rivers, constituting what are called the hydrographic network. This immense polarized network channels the water toward a single receptacle: an ocean. Gravity dominates this entire step in the cycle because water tends to minimize its potential energy by running from high altitudes toward the reference point, that is, sea level.
The rate at which a molecule of water passes though the cycle is not random but is a measure of the relative size of the various reservoirs. If we define residence time as the average time for a water molecule to pass through one of the three reservoirs — atmosphere, continent, and ocean — we see that the times are very different. A water molecule stays, on average, eleven days in the atmosphere, one hundred years on a continent and forty thousand years in the ocean. This last figure shows the importance of the ocean as the principal reservoir of the hydrosphere but also the rapidity of water transport on the continents.
A vast chemical separation process takes places during the flow of water over the continents. Soluble ions such as calcium, sodium, potassium, and some magnesium are dissolved and transported. Insoluble ions such as aluminum, iron, and silicon stay where they are and form the thin, fertile skin of soil on which vegetation can grow. Sometimes soils are destroyed and transported mechanically during flooding. The erosion of the continents thus results from two closely linked and interdependent processes, chemical erosion and mechanical erosion. Their respective interactions and efficiency depend on different factors.
地球表面的地质由水的特殊性质决定。水以固体，液体和气态存在于地球上，因此具有特别的反应性。它溶解，运输和沉淀许多化合物，并不断改变地球的表面。 从海洋中蒸发，水蒸气形成云，其中一些通过风在大陆上运输。来自云层的凝结提供了大陆侵蚀的基本因素：雨。水沉淀在地面上，水滴流形成溪流，溪流和河流，形成所谓的水文网络。这个巨大的极化网络将水引向一个容器：海洋。重力在循环的整个步骤中占主导地位，因为水通过从高海拔向参考点（即海平面）运行而倾向于最小化其潜在能量。 水分子通过循环的速率不是随机的，而是各种储层相对大小的量度。如果我们将停留时间定义为水分子通过三个水库之一（大气层，大陆和海洋）的平均时间，我们会发现时间是非常不同的。水分子平均在大气中停留11天，在大陆上停留100年，在海洋中停留4万年。最后的数字显示了海洋作为水圈主要储层的重要性，以及大陆水运的快速性。 在大陆上空的水流过程中发生了巨大的化学分离过程。可溶性离子如钙，钠，钾和一些镁被溶解和运输。不溶性离子如铝，铁和硅留在原处，形成植物可以生长的土壤肥沃的肥沃土壤。有时土壤在洪水期间被破坏并以机械方式运输。因此，大陆的侵蚀是由两个紧密相连和相互依存的过程，即化学侵蚀和机械侵蚀造成的。它们各自的相互作用和效率取决于不同的因素