翻译

Surface Fluids on Venus and Earth

地球和金星表面的流体

A fluid is a substance, such as a liquid or gas, in which the component particles (usually molecules) can move past one another. Fluids flow easily and conform to the shape of their containers. The geologic processes related to the movement of fluids on a planet's surface can completely resurface a planet many times. These processes derive their energy from the Sun and the gravitational forces of the planet itself. As these fluids interact with surface materials, they move particles about or react chemically with them to modify or produce materials. On a solid planet with a hydrosphere and an atmosphere, only a tiny fraction of the planetary mass flows as surface fluids. Yet the movements of these fluids can drastically alter a planet. Consider Venus and Earth, both terrestrial planets with atmospheres.

流体是物质，比如液体和气体，它们的组成部分（通常是分子）可以相互移动，流体流动很容易而且形状可以适应它们的容器。地表流体的移动造成的地质演化可以让星球表面彻底改变很多次。太阳能和自身的引力促使了这些地址过程。当这些流体和星球表面的物质发生反应，他们移动粒子和他们发生化学反应来改变或者重新创造新的物质，在一个拥有水圈和大气层的行星上，行星表面的流体只占总质量的一小部分。但是这部分的流体能彻底的改变行星，比如金星和地球，这两个类地行星都有大气层。

Venus and Earth are commonly regarded as twin planets but not identical twins. They are about the same size, are composed of roughly the same mix of materials, and may have been comparably endowed at their beginning with carbon dioxide and water. However, the twins evolved differently largely because of differences in their distance from the Sun. With a significant amount of internal heat, Venus may continue to be geologically active with volcanoes, rifting, and folding.However, it lacks any sign of a hydrologic system (water circulation and distribution): there are no streams, lakes oceans or glaciers.Space probes suggest that Venus may have started with as much water as Earth, but it was unable to keep its water in liquid form.Because Venus receives more heat from the Sun, water released from the interior evaporated and rose to the upper atmosphere where the Sun's ultraviolet rays broke the molecules apart.Much of the freed hydrogen escaped into space, and Venus lost its water. Without water, Venus became less and less like Earth and kept an atmosphere filled with carbon dioxide. The carbon dioxide acts as a blanket, creating an intense greenhouse effect and driving surface temperatures high enough to melt lead and to prohibit the formation of carbonate minerals. Volcanoes continually vented more carbon dioxide into the atmosphere. On Earth, liquid water removes carbon dioxide from the atmosphere and combines it with calcium, from rock weathering, to form carbonate sedimentary rocks. Without liquid water to remove carbon from the atmosphere, the level of carbon dioxide in the atmosphere of Venus remains high.

金星和地球普遍被认为是一对双胞胎行星，但不是完全一样。他们有同样的大小，同样的物质组成，在最初的时候都有二氧化碳和水。但是他们演化的过程却有很大的不同，因为他们和太阳的距离不一样。金星内部有巨大的热量，地质活动非常活跃，火山，裂陷，折叠等地质活动可以一直很活跃。但是，他缺少水圈的迹象（水循环和分发），没有急流，湖，海，或冰川。空间探测器发现金星可能和地球一样早拥有水，但是他没法让水保持液态。因为金星从太阳得到更多的热能。水从内部蒸发，上升到大气层，太阳紫外线分解水分子。释放的氢气逃到了外太空，然后金星失去了水，没有水，金星和地球越来越不像，大气中充满了二氧化碳，二氧化碳像一个摊子，造成了温室效应是的地表变得很高足够融化铅让后组织了碳酸盐矿物的形成。频繁的火山爆发造成了大量的二氧化碳排放到大气中，在地球上，液态水移除了大气中的二氧化碳使它和钙物质发生反应，从岩石风化，到形成碳酸盐沉积岩石，没有液态水把二氧化碳从大气中移除，金星大气中的二氧化碳含量很高。

Like Venus, Earth is large enough to be geologically active and for its gravitational field to hold an atmosphere. Unlike Venus, it is just the right distance from the Sun so that temperature ranges allow water to exist as a liquid, a solid, and a gas. Water is thus extremely mobile and moves rapidly over the planet in a continuous hydrologic cycle. Heated by the Sun, the water moves in great cycles from the oceans to the atmosphere, over the landscape in river systems, and ultimately back to the oceans. As a result, Earth's surface has been continually changed and eroded into delicate systems of river valleys - a remarkable contrast to the surfaces of other planetary bodies where impact craters dominate. Few areas on Earth have been untouched by flowing water. As a result, river valleys are the dominant feature of its landscape. Similarly, wind action has scoured fine particles away from large areas, depositing them elsewhere as vast sand seas dominated by dunes or in sheets of loess (fine-grained soil deposits). These fluid movements are caused by gravity flow systems energized by heat from the Sun. Other geologic changes occur when the gases in the atmosphere or water react with rocks at the surface to form new chemical compounds with different properties. An important example of this process was the removal of most of Earths carbon dioxide from its atmosphere to form carbonate rocks. However, if Earth were a little closer to the Sun, its oceans would evaporate; if it were farther from the Sun, the oceans would freeze solid. Because liquid water was present, self-replicating molecules of carbon, hydrogen, and oxygen developed life early in Earth's history and have radically modified its surface, blanketing huge parts of the continents with greenery. Life thrives on this planet, and it helped create the planet's oxygen- and nitrogen-rich atmosphere and moderate temperatures.

像金星一样，地球足够大，地质足够活跃，引力能维持大气层，不像金星，地球和太阳刚刚好的距离，温度范围可以让水保持业态，固态，和气态，一个结果就是，水可以在地球上的水圈中很快的流动，让后被太阳加热，水形成了一个循环从海洋到大气层，经过从河流系统，然后最终回到海洋，结果，地球表面被精妙的河谷系统不断的改变和侵蚀，和其他的以陨石坑占主导的其他星球表面形成一个巨大的反差。只有很少的地方没有被流动的水接触。结果，河谷在地标占据了主要地位。同样的，风的活动把一些细小的微粒从一个地方吹到了另一个地方，成为了沙漠和黄土，组成了沙海（精细的土壤沉积）。这些流动是由于被太阳加热引力系统引起的，当大气和水中的气体和地表的岩石发生反应，形成新的拥有不同的属性的化学物质时，就会形成其他的地质变化。一个重要的例子，这个过程使得大气中的二氧化碳减少形成了碳酸盐岩石。然而，如果地球和太阳在近一点，它的海洋就会蒸发，如果离太阳更远一点的话，海洋就会变成结冰的固态。因为有液态水，自我复制的碳，氢，氧分子在地球上发展出了生命，然后彻底的改变了它的表面，用绿色植物遮盖住了大部分的陆地。生命在这个地球上繁荣发展，创造出了这个星球的由氧气氮气组成的空气和适宜的温度。