科学美国人60秒 SSS Climate Cycles Could Have Carved Canyons on Mars
时间：2018-12-24 作者：英语课 分类：2017年Scientific American(一)月
The surface of Mars is etched with ancient river valleys and lake basins. Which makes researchers think that liquid water once flowed on the Red Planet. But how? Today, Mars is too cold for much, if any, liquid water to exist. And 3.8 billion years ago, when the flowing water features formed, the sun was fainter than it is today, making it even harder to imagine a balmy Martian climate. That’s why many researchers think Mars may have gone in and out of deep freezes.
“The real questions have been: for how long was it warm, and what was the mechanism 1 for warming it up.”
James Kasting, a geologist 2 at Penn State University. He shared his take on the problem at the December meeting of the American Geophysical Union in San Francisco, and in the journal Earth and Planetary Science Letters. [Natasha E. Batalha et al., Climate cycling on early Mars caused by the carbonate–silicate cycle]
Some researchers have suggested that early Mars only thawed 3 out when large asteroid 4 impacts or volcanic 5 eruptions 6 temporarily warmed the planet. But Kasting and others think warm windows from such dramatic events would have been too brief to carve the vast canyons 7 that exist on Mars. Now, Kasting and his colleagues have come up with an alternative explanation: they think Mars may have experienced a series of climate cycles caused by changes in the strength of the greenhouse effect.
The idea goes like this: when Mars was cold and frozen, volcanoes continued to belch 8 out the greenhouse gases carbon dioxide and hydrogen into the atmosphere. There, the gas blanket trapped heat and warmed the planet up until liquid water began to flow, forming Mars’ rivers and lakes. However, warm temperatures and abundant water would also have sped up certain chemical reactions that consumed carbon dioxide, reducing the greenhouse effect and cooling the planet back down again. Then the cycle would repeat.
“Which is similar to what the impact people have been arguing, except that when it gets warm, it can stay warm for millions of years instead of thousands of years.”
So far, Kasting’s team has only shown that such an explanation is possible, according to climate models. But the researchers say NASA’s Curiosity rover and other future Mars missions could help test the idea by looking for evidence of multiple warm events, and their durations. Perhaps, hidden in the dry Martian dust lie clues to a surprisingly soggy past.
—Julia Rosen
- The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
- The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。
- The geologist found many uncovered fossils in the valley.在那山谷里，地质学家发现了许多裸露的化石。
- He was a geologist,rated by his cronies as the best in the business.他是一位地质学家，被他的老朋友们看做是这门行当中最好的一位。
- The little girl's smile thawed the angry old man. 小姑娘的微笑使发怒的老头缓和下来。 来自《简明英汉词典》
- He thawed after sitting at a fire for a while. 在火堆旁坐了一会儿，他觉得暖和起来了。 来自《简明英汉词典》
- Astronomers have yet to witness an asteroid impact with another planet.天文学家还没有目击过小行星撞击其它行星。
- It's very unlikely that an asteroid will crash into Earth but the danger exists.小行星撞地球的可能性很小，但这样的危险还是存在的。
- There have been several volcanic eruptions this year.今年火山爆发了好几次。
- Volcanic activity has created thermal springs and boiling mud pools.火山活动产生了温泉和沸腾的泥浆池。
- There have been several volcanic eruptions this year. 今年火山爆发了好几次。 来自《简明英汉词典》
- Over 200 people have been killed by volcanic eruptions. 火山喷发已导致200多人丧生。 来自辞典例句