第一篇：

　　洋流

　　海水在季風(fēng)和地轉(zhuǎn)偏向力(Coriolis Force)的作用下產(chǎn)生洋流，洋流分為上下兩層。上層溫暖密度小，下層含鹽多密度大，這兩層各自流動不混合。

　　上層帶著溫暖海水向兩極流動，在極地地區(qū)變冷，結(jié)冰使得鹽分析出，密度變大而下沉成為下層洋流。下層洋流流回赤道。

　　兩層混合的地方發(fā)生在風(fēng)與海岸平行的地方，這里的風(fēng)在地轉(zhuǎn)偏向力的作用下把上層洋流推離海岸，于是下層洋流向上補(bǔ)充。洋流混合對生態(tài)有很大作用，因?yàn)榘押Ｑ笊�物死亡后沉到下層然后被分解的營養(yǎng)帶到上層。滋養(yǎng)植物-浮游生物-更高級消費(fèi)者。

　　洋流對流經(jīng)的地區(qū)的氣候有重要英雄。

　　洋流還與全球氣候變暖聯(lián)系在一起，因?yàn)槎�氧化碳可以溶在海水里然后沉淀到海底�?/P>

　　解析：本文屬于地理地質(zhì)類文章，講述的是洋流的形成過程。地理地質(zhì)類文章屬于托福閱讀中不太陌生的話題，但是從機(jī)經(jīng)判斷，本文屬于流程類講解方式，流程類文章在托福閱讀里不是很常見，而且出現(xiàn)時，往往對學(xué)員的邏輯性考核較強(qiáng)，在備考時需要額外關(guān)注。類似流程類文章可以參考TPO18的Lightning.

　　參考閱讀：

　　Lightning is a brilliant flash of light produced by an electrical discharge from a storm cloud. The electrical discharge takes place when the attractive tension between a region of negatively charged particles and a region of positively charged particles becomes so great that the charged particles suddenly rush together. The coming together of the oppositely charged particles neutralizes the electrical tension and releases a tremendous amount of energy, which we see as lightning. The separation of positively and negatively charged particles takes place during the development of the storm cloud.

　　The separation of charged particles that forms in a storm cloud has a sandwich-like structure. Concentrations of positively charged particles develop at the top and bottom of the cloud, but the middle region becomes negatively charged. Recent measurements made in the field together with laboratory simulations offer a promising explanation of how this structure of charged particles forms. What happens is that small (millimeter-to centimeter-size) pellets of ice form in the cold upper regions of the cloud. When these ice pellets fall, some of them strike much smaller ice crystals in the center of the cloud. The temperature at the center of the cloud is about -15℃ or lower. At such temperatures, the collision between the ice pellets and the ice crystals causes electrical charges to shift so that the ice pellets acquire a negative charge and the ice crystals become positively charged. Then updraft wind currents carry the light, positively charged ice crystals up to the top of the cloud. The heavier negatively charged ice pellets are left to concentrate in the center. This process explains why the top of the cloud becomes positively charged, while the center becomes negatively charged. The negatively charged region is large: several hundred meters thick and several kilometers in diameter. Below this large, cold, negatively charged region, the cloud is warmer than -15℃, and at these temperatures, collisions between ice crystals and falling ice pellets produce positively charged ice pellets that then populate a small region at the base of the cloud.

　　Most lightning takes place within a cloud when the charge separation within the cloud collapses. However, as the storm cloud develops, the ground beneath the cloud becomes positively charged and lightning can take place in the form of an electrical discharge between the negative charge of the cloud and the positively charged ground. Lightning that strikes the ground is the most likely to be destructive, so even though it represents only 20 percent of all lightning, it has received a lot of scientific attention.

　　Using high-speed photography, scientists have determined that there are two steps to the occurrence of lightning from a cloud to the ground. First, a channel, or path, is formed that connects the cloud and the ground. Then a strong current of electrons follows that path from the cloud to the ground, and it is that current that illuminates the channel as the lightning we see.

　　The formation of the channel is initiated when electrons surge from the cloud base toward the ground. When a stream of these negatively charged electrons comes within 100 meters of the ground it is met by a stream of positively charged particles that comes up from the ground. When the negatively and positively charged streams meet, a complete channel connecting the cloud and the ground is formed. The channel is only a few centimeters in diameter, but that is wide enough for electrons to follow the channel to the ground in the visible form of a flash of lightning. The stream of positive particles that meets the surge of electrons from the cloud often arises from a tall pointed structure such as a metal flagpole or a tower. That is why the subsequent lightning that follows the completed channel often strikes a tall structure.

　　Once a channel has been formed, it is usually used by several lightning discharges, each of them consisting of a stream of electrons from the cloud meeting a stream of positive particles along the established path. Sometimes, however, a stream of electrons following an established channel is met by a positive stream making a new path up from the ground. The result is a forked lightning that strikes the ground in two places.

　　第二篇：

　　地球大氣

　　太陽大氣反映了太陽系形成初期的成份構(gòu)成，但地球現(xiàn)在的大氣與那時的顯著不同。原始大氣在太陽風(fēng)和隕石的作用下被剝離地球，然后地球的火山排氣作用(outgassing)形成了現(xiàn)在大氣的各種主要成分，但不包括氧氣。

　　相較現(xiàn)在20%的氧氣，一開始地球只有很少量的氧，這些氧主要試大氣中的水發(fā)生光解作用(photo dissociation)產(chǎn)生的而那些大量的氧是由植物光合作用(photosynthesis)發(fā)生的。氧氣和海洋里的鐵發(fā)生氧化，會沉淀到海底，氧氣多的時期形成紅色的氧化鐵，少的時候會形成黑色的，于是海底有些時候就呈現(xiàn)帶狀(這里有年份具體忘了)

　　地球上的氧氣還會變成臭氧，臭氧可以阻擋紫外線保護(hù)地球上的生命。臭氧在某個時間段內(nèi)增加，在差不多結(jié)束的那段時間有個生命形式的爆發(fā)。

　　解析：本文同第一篇，屬于地理地質(zhì)類文章，講述的是地球大氣的構(gòu)成。地理地質(zhì)類文章是屬于托福閱讀中不太陌生的話題，但是因?yàn)橹v解內(nèi)容較為晦澀，也是學(xué)員理解不是太好的內(nèi)容，在備考前需要額外關(guān)注，并且仔細(xì)分析，避免因?yàn)樘厥獗尘盎蛘邔W(xué)科詞匯不熟悉導(dǎo)致閱讀速度及理解程度受影響。

　　參考閱讀：

　　Outgassing from volcanism, supplemented by gases produced during the late heavy bombardment of Earth by huge asteroids, produced the next atmosphere, consisting largely of nitrogen plus carbon dioxide and inert gases. A major part of carbon-dioxide emissions soon dissolved in water and built up carbonate sediments.

　　Researchers have found water-related sediments dating from as early as 3.8 billion years ago. About 3.4 billion years ago, nitrogen formed the major part of the then stable "second atmosphere". An influence of life has to be taken into account rather soon in the history of the atmosphere, because hints of early life-forms appear as early as 3.5 billion years ago. How Earth at that time maintained a climate warm enough for liquid water and life, if the early Sun put out 30% lower solar radiance than today, is a puzzle known as the "faint young Sun paradox".

　　The geological record however shows a continually relatively warm surface during the complete early temperature record of Earth - with the exception of one cold glacial phase about 2.4 billion years ago. In the late Archean eon an oxygen-containing atmosphere began to develop, apparently produced by photosynthesizing cyanobacteria (see Great Oxygenation Event), which have been found as stromatolite fossils from 2.7 billion years ago. The early basic carbon isotopy (isotope ratio proportions) very much approximates current conditions, suggesting that the fundamental features of the carbon cycle became established as early as 4 billion years ago.

　　Ancient sediments in the Republic of Gabon dating from between about 2,150 and 2,080 million years ago provide a record of Earth's dynamic oxygenation evolution. These fluctuations in oxygenation were likely driven by the Lomagundi carbon isotope excursion.

　　The constant re-arrangement of continents by plate tectonics influences the long-term evolution of the atmosphere by transferring carbon dioxide to and from large continental carbonate stores. Free oxygen did not exist in the atmosphere until about 2.4 billion years ago during the Great Oxygenation Event and its appearance is indicated by the end of the banded iron formations. Before this time, any oxygen produced by photosynthesis was consumed by oxidation of reduced materials, notably iron. Molecules of free oxygen did not start to accumulate in the atmosphere until the rate of production of oxygen began to exceed the availability of reducing materials. This point signifies a shift from a reducing atmosphere to an oxidizing atmosphere. O2 showed major variations until reaching a steady state of more than 15% by the end of the Precambrian. The following time span from 541 million years ago to the present day is the Phanerozoic eon, during the earliest period of which, the Cambrian, oxygen-requiring metazoan life forms began to appear.

　　The amount of oxygen in the atmosphere has fluctuated over the last 600 million years, reaching a peak of about 30% around 280 million years ago, significantly higher than today's 21%. Two main processes govern changes in the atmosphere: Plants use carbon dioxide from the atmosphere, releasing oxygen. Breakdown of pyrite and volcanic eruptions release sulfur into the atmosphere, which oxidizes and hence reduces the amount of oxygen in the atmosphere. However, volcanic eruptions also release carbon dioxide, which plants can convert to oxygen. The exact cause of the variation of the amount of oxygen in the atmosphere is not known. Periods with much oxygen in the atmosphere are associated with rapid development of animals. Today's atmosphere contains 21% oxygen, which is high enough for this rapid development of animals.

　　第三篇：

　　石器時代

　　介紹了一個人類學(xué)家的看法。他認(rèn)為石器時代的人比現(xiàn)代人更富裕，好像是因?yàn)槭�器時代的人欲望更少更易滿足。他們限制人口，除了吃的比大的部落飽還可以避免一些疾病。因?yàn)槭�器時代的人到處探索，除了個別太惡劣的環(huán)境，吃的都是富足的。(這篇各個點(diǎn)比較散亂還集中在一個段落，記不住)

　　石器時代的人工作比較少只有4、5小時，他們有很多休閑時間。然后比較各個時期的工作時間，逐漸增加，現(xiàn)代之前一個最高9.5h，現(xiàn)代稍微回落一點(diǎn)。因?yàn)樯鐣�發(fā)展需要一個比較安定的生活，因此家庭花在家政(household)方面的時間增多，但男人花在家政煩嗎比例有所下降。

　　最后說了一下學(xué)界的評論。忘了是作者的觀點(diǎn)還是學(xué)界的觀點(diǎn)，說他是overstatement。但文章最后一句話我理解是：認(rèn)為石器時代的人富足不是因?yàn)樗麄兩�產(chǎn)比現(xiàn)代更多的東西，而且因?yàn)樗麄兊挠�望更少�?/P>

　　解析：本文屬于人文類文章，關(guān)注的是石器時代人的生活。人文類文章屬于托福閱讀的�？純�(nèi)容，從機(jī)經(jīng)來看本文講解的具體內(nèi)容，涉及到的專業(yè)詞匯量比較小，在理解時詞匯方面的難度應(yīng)該不大，但是一般人文類文章因?yàn)榫渥悠�長而給學(xué)生帶來理解障礙，在備考時需要做專門的長難句準(zhǔn)備。

　　參考閱讀：

　　The Stone Age was a time thousands of years ago, when humans lived in caves and jungles. Life was simple, and there were only two main things to do – to protect themselves from the wild animals and to gather food. It started almost with the evolution of mankind.

　　For both purposes, people made tools from stone. The oldest stone tool that we have as an evidence is almost 3.4 million years old . It was found in Lower Awash Valley in Ethiopia. Stones were also used to make fire. Since in those times, humans used stone for almost everything they did, hence the name Stone Age. To look at a timeline of this period click here.

　　The Stone Age went on for a long time. Obviously in the beginning of the Stone Age rock shelters were the way to go. Any signs of trouble and the humans would go hiding in the caves. In India, the Bhimbetka rock shelters show the earliest signs of human life in the region. They are almost 30,000 years old. Some researchers have discovered Stone Age art in European caves. The inside walls of the cave are adorned with paintings of animals like horses, deer, and mammoths.

　　One of the most important advancements in human history was the development and use of tools. Tools allowed hominids to become the masters of their environments, to hunt, to build, and to perform important tasks that made life easier for them. The first tools were made out of stone. Thus, historians refer to the period of time before written history as the Stone Age.

　　Hunter gatherers often painted and engraved the inside of caves and huts.

　　The Palaeolithic people decorated their cave walls either by carving or engraving them with sharp stones, or by painting them with pigment made from minerals. Red (rust) colours were obtained from the stones and black came from charcoal. The colours were mixed with water to make paint. They were applied to the walls with either their fingers, fur or brushes made from twigs. The paintings often represented daily life such as men hunting, animals, women gathering crops.