7. 碳循环

　　本月原始:V1(by 你是不沉岛)内容就是碳循环 第二段有提到“新的rock会吸收碳”之类的

　　V2:(by Oliviahk)讲多少多少年前warmer,wetter的气候现在没有了，而且经常会出现极端天气(有题)，然后作者开始探究原因。后面分两段，介绍了两派(school)观点。第一派说到continent，sea，inland sea的组成不一样了，所以影响了气候(第一派记得不是很清楚了，主要考第二段)第二派讲因为现在空气中的二氧化碳更少了，而二氧化碳是可以保温的。因为下雨的时候二氧化碳和水可以形成碳酸，然后腐蚀石头，就这样被消耗了。而且海洋里的生物也会吸收二氧化碳里的碳，然后通过排泄啊啥的方式碳就到了seafloor。虽然第二种方式碳最终还是会上升到大气层，但是要花几百万年的时间。然后还有一个人说，现在的地质运动更激烈，(有题)更促进了二氧化碳的腐蚀。因为是斜坡，然后被腐蚀的石头就能很快滚下来然后新的石头继续被腐蚀(好像还有其他的precipitation啥的记不大清楚了)

　　悦读菌考古版

　　V1: Scarlettma

　　现在的climate越来越冷了，因为2种原因。第一段列出的是因为大陆板块 海洋的变化引起的，第二段就说是因为大气层二氧化碳引起的，就说二氧化碳到了海里面，然后被海洋生物还是什么吸收，然后又被排出，留在seabed上面，再影响气候……好像是这意思，就说这个周期是很长很长的。

　　1 iamcrystal 710 题目考到什么削弱第二段里的观点，有第二段可以推出什么结论，总之就是大多在第二段里找，注意下hundreds of million years，还有4000million years都是些细节定位的地方，在中间和靠后的都有信息要找。

　　2 200702061 710：果然看见了传说中的整段HIGHLIGHT啊。那叫一个壮观，屏幕都变黄色了。

　　3 gitarrelieber 730 V37 下面的陈述中除了哪个都支持了第二段中那个学派的观点：A- 新的石头(fresh rock)可以吸收更多的二氧化碳/B- 大陆和海洋的相对移动造成地球降温

　　4 gitarrelieber 730 V37 根据第二段的理论下面除了哪个都是正确的：A- chemical weathering 需要水/B- Uplift是吸收的二氧化碳的主要因素

　　(综合版)

　　两段长篇

　　科学家发现最近40million years，地球不再是原来那么warm和wet了(此处有题)，先给出了一个流派的若干解释：随着二氧化碳的增多，大气的降水中融解了二氧化碳，这些水降到海面，被各种过程吸收，然后沉积到海底，虽然到海底这些c最终还是要回到大气中，但是这个过程需要hundreds of millions of years(隐含40百万年对它来说是相对短的过程，此处有题)，另外陆面也对二氧化碳的吸收起到一定作用，而且随着内海的面积逐渐减少，陆面的面积越来越大因而吸收c也越多。第一段的末尾说这个解释不错，但作为唯一的解释未免不让人信服。

　　第二段是讲好像叫M R的人提出一种观点，对第一段的解释起到支持作用，他说地质演变抬高了陆地某些位置，高了之后会有更多的fresh岩石吸收c，而且因为抬高了后这些位置比较陡，降水可以更好的冲走这些吸收了c的岩石。提出的新观点觉得有二个重要原因

　　a. weathering的过程　(即对第一段的解释起到支持作用); b. 岩石陆地的上升strengthen了weathering的过程

　　1.一个题目在第一段，问现在环境跟原来环境有什么区别，选择较Warm, Wet(此题也许是取非题，问现在的环境怎么样，那以前的来取非)

　　2. 第二段，这个过程(二氧化碳溶解沉入海底再回到大气这个过程)需要hundreds of millions of years(隐含40百万年对它来说是相对短的过程，此处有题)

　　3. 有一个Except题 (注意第二段中的机理讨论部分)

　　4.然后有一个应该是取非条件的(注意第二段中的机理讨论部分)

　　5.R科学家提出，有逻辑题，以下哪项weaken了R的观点，定位于二段后半部分. 注意R的观点有两个部分　a.weathering的过程　(即对第一段的解释起到支持作用); b.岩石陆地的上升strengthen了weathering的过程.这题要削弱的应该是第二个观点

　　6.第二段全划线，机理题

　　(疑似)原文未删减 gitarrelieber 730 V37考后感：很有帮助，基本上和考试文章一致

　　节选自Plateau Uplift and Climate Change (Scientific American Magazine @ March 1991)

　　Author：William F. Ruddiman and John E. Kutzbach

　　During the past 40 million years, and particularly during the past 15 million years, this warm, wet climate largely disappeared. Colder climates and much greater regional extremes of precipitation have developed. What caused this cooling and diversification of climate and vegetation into a complex mosaic of many regionally distinctive types?

　　One school of thought focuses on the changing positions of the earth’s continents and oceans. The Atlantic Ocean has expanded at the expense of the Pacific Ocean, whereas an ancient equatorial sea that extended across much of Eurasia (called the Tethys Sea) has shrunk to become the modern, much smaller Mediterranean Sea. In addition, the fraction of continents flooded by shallow inland seas has slowly decreased, exposing large amounts of land and creating climates less moderated by the temperature-stabilizing effects of oceans. Computer model simulations show that changes in the arrangement of the continents and the size of inland seas can have important effects on global climate over very long intervals of geologic time. But they are significantly less convincing as sole explanations for the dramatic changes of the past 40 million years.

　　Another possibility is a long-term decline in the concentration of carbon dioxide in the atmosphere, which would lessen the amount of heat trapped by the atmosphere and lead to “greenhouse cooling.” The amount of carbon dioxide in the earth’s atmosphere over million-year timescales is controlled by two major processes. Chemical weathering of continental rocks removes carbon dioxide from the atmosphere and carries it in dissolved chemical from to the ocean, where it is taken in by marine biota and deposited in sediments on the seafloor. Tectonic activity eventually frees this trapped carbon dioxide, in the earth’s lithospheric plates transports the seafloor to ocean trenches, where subduction carries old crust and sediments down toward the earth’s hot interior. At great depths, the sediments melt, releasing carbon dioxide, which emerges from the volcanic islands that overlie the buried curst and rejoins the atmosphere, completing the cycle.

　　If the pace of seafloor spreading (and hence of subduction) slowed significantly, less carbon dioxide would be vented to the atmosphere, the atmosphere would become relatively depleted of carbon dioxide and temperatures would fall. In fact, globally averaged seafloor spreading rates slow little or no net change in the past 40 million years. Subduction and volcanism eventually return the carbon dioxide to the atmosphere, but this process requires a long time (tens to hundreds of millions of years) to complete.

　　Plateau uplift may alter climate by increasing chemical weathering of rocks, thereby reducing atmospheric carbon dioxide concentrations. Carbon dioxide combines with rainwater and ground water to form carbonic acid, which reacts with silicate minerals in rocks during weathering. The resulting bicarbonate ions drain into the oceans, where they are taken up by marine animals such as plankton and corals and eventually deposited on the seafloor. The net effect is that chemical weathering removes carbon dioxide from the atmosphere and locks it away at the bottom of the oceans.

　　Maureen Raymo proposed that uplift of plateaus and mountain ranges has increased the rate of chemical erosion of continental rock on the globally averaged basis. Uplift could enhance chemical weathering in several ways. Heavy monsoons, which develop at the margins of plateaus, unleash particularly intense rainfall. In these regions, uplift-related faulting and folding also expose fresh rock to the weathering process. Moreover, the steeper slopes created by plateau uplift cause faster runoff, which removes erosion products and intensifies the chemical attack on the rock. Raymo suggests that long-term uplift in Tibet and other regions may have increased the rate at which carbon dioxide is removed from the atmosphere. In this way, concentrations would have fallen even though the amount of carbon dioxide exhaled by volcanoes (as inferred from seafloor spreading rates) remained nearly constant. Falling carbon dioxide levels would reduce the ability of the atmosphere to retain heat, thereby amplifying the global cooling.