托福阅读生物爆发与灭绝的知识内容
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托福阅读生物爆发与灭绝的知识内容
我们一共经历了一次大爆发，和五次大灭绝。但大家也要知道，我们现在正在经历第六次物种大灭绝。
寒武纪大爆发(Cambrian explosion)——5.4亿年前
奥陶纪大灭绝(Ordovician extinction)——4.4亿年前
泥盆纪大灭绝(Devonian extinction)——3.65亿年前
二叠纪大灭绝(Permian extinction)——2.5亿年前
三叠纪大灭绝(Triassic extinction)——2亿年前
白垩纪大灭绝(Cretaceous extinction)——6500万年前
寒武纪大爆发
寒武纪大爆发(Cambrian explosion)被称为古生物学和地质学上的一大悬案!自达尔文以来就一直困扰着进化论等学术界。
大约5亿4200万年前到5亿3000万年前，在地质学上称作寒武纪的开始，绝大多数无脊椎动物(invertebrate)在这2000多万年时间内出现。
这种几乎是“同时地”、“突然地”在2000多万年时间内出现在寒武纪地层中的无脊椎动物化石(节肢动物arthropod、软体动物、环节动物等)，而在寒武纪之前更为古老的地层中长期以来却找不到动物化石的现象，被古生物学家称作“寒武纪生命大爆发”，简称“寒武纪爆发”。
这也是显生宙(Phanerozoic eon)的开始
100多年以来，有两种基本观点
一种观点认为，寒武爆发是一种假象，这是某些达尔文或新达尔文主义(Darwinism)者所支持的观点。
由于进化是渐进的，所谓“爆发”只是表明首次在生物化石记录中发现了早在前寒武纪就已经广泛存在并发展的生物，其他的生物化石群可能是由于地质记录的不完全而“缺档”。
造成这种“缺档”的原因是前寒武纪地层(stratum)经历着热与压力，其中的化石被销毁了。
由于发现钱寒武纪化石沉积层(sedimentary formation)中存在大量细菌(bacteria)和蓝藻(blue-algae)这样的原核生物(prokaryotic organism)，因而这一解释不再有说服力。
另一种观点认为，寒武纪爆发代表了生物进化过程中的真实事件名科学家从物理环境和生态环境的变化两个方面来解释这一现象。
1965年，两位美国物理学家提出了寒武纪爆发是由于地球大气的氧水平(atmospheric)这个物理原因造成的。
他们认为，在早期地球的大气中含有很少或根本没有自由氧，氧是前寒武纪(Precambrianperiod)藻类植物光合作用(photosynthesis)的产物并逐渐积累(accumulation)形成的。
后生动物需要大量的氧，一方面用于呼吸作用(respiration)，另一方面氧还以臭氧(ozonic)的形式在大气中吸收大量有害的紫外线(ultraviolet ray)，使后生动物免于有害辐射的损伤。
生物大灭绝
生物大灭绝(Biological extinction)是指大规模的集群灭绝，生物灭绝有叫生物绝种。
在集群灭绝(mass extinction)过程中，往往是整个分类单元中的所有物种，无论在生态系统中的地位高低，都逃不过劫难(catastrophe)
大规模的集群灭绝有一定的周期性(periodic)，大约6200万年就会发生一次，但集群灭绝对动物的影响最大，而陆生植物(terrestrialplant)的集群灭绝不像动物那样显著
奥陶纪大灭绝
第一次物种大灭绝发生在4亿4千万年前的奥陶纪末期(Ordovicianperiod)，由于当时气候变冷并且海平面下降，生活在水体的各种不同的无脊椎动物便荡然无存
在大约4.4亿年前，撒哈拉坐在的陆地曾经位于南极(the Antarctic Pole)，当陆地汇集在极点附近时，容易造成厚的积冰。大片的冰川(glacier)使洋流(ocean current)和大气环流(generalatmospheric circulation)变冷，整个地球的温度下降，冰川锁住水，海平面降低，原先丰富的沿海生态系统被破坏，导致85%的物种灭绝。
泥盆纪大灭绝
第二次物种大灭绝发生在泥盆纪晚期(Devonian)，其原因也是地球气候变冷河海洋退却。
在距今3.65亿年前的泥盆纪后期，经历了两个高峰，中间间隔100万年，发生地球史上第二次物种灭绝事件，海洋生物遭到重创。
二叠纪大灭绝
第三次物种大灭绝发生在距今2.5亿年前的二叠纪末期(Permian)，发生了有史以来最严重的大灭绝事件，估计地球上有96%的物种灭绝，其中90%的海洋生物和70%的陆地脊椎动物灭绝。重要珊瑚(coral)群全部消失。
这次大灭绝使得生态系统获得了一次最彻底的更新，为恐龙等爬行类动物(reptile)的进化铺平了道路。
这一次大灭绝是地球历史上从古生代(Paleozoic)向中生代(Mesozoic)转折的里程碑。
在二叠纪曾经发生海平面下降和大陆漂移(continental drift)，造成了最严重的物种大灭绝。所有的大陆聚集成了一个联合的盘古大陆(archicontinent)，海岸线急剧减少，大陆架(continental shelf)也缩小了，很多生物失去了生存空间。
更严重的是，当浅层的大陆架暴露出来后，原先埋藏在海底的有机质(organic matter)被氧化(oxidization)，这个过程消耗了氧气，释放出二氧化碳(carbon dioxide)，大气中氧含量减少对陆地生物的生存造成了巨大的伤害。
三叠纪大灭绝
第四次物种大灭绝发生在距今1.95亿年前的三叠纪末期(Triassic period)，有76%的物种灭绝，其中主要为海洋生物，这次大灭绝并无明显的标志，只发现海平面下降之后又上升，出现大面积缺氧的海水。
白垩纪大灭绝
科学家们推断第五次物种大灭绝是由小行星撞击而发生的，这次撞击相当于人类历史上发生过最强烈地震(seismic)的100万倍，爆炸的能量相当于地球上核武器总量爆炸的1万倍，导致了2.1万立方公里的物质进入大气中。
由于大气中大量高密度(high-density)的尘埃，太阳光不能照射到地球上，导致地球表面温度迅速降低。
没有阳光，植物逐渐枯萎(withered)死亡;没有植物，植食性(phytophagous)的恐龙饥饿而死;没有植食性动物，肉食性(sarcophagy)的恐龙失去食物来源，在绝望和相互杀戮中缓慢消亡。
几乎所有的大型陆生动物都未能幸免于难。小型的陆生动物(terrestrial animal)，像一些哺乳动物(mammal)依靠残余的食物勉强为生，终于熬过了最艰难的日子，等到了古近纪(Paleogene)陆生脊椎动物迎来了再次的大繁荣。
撞击假说的支持者发现了许多有力的证据。最有力的证据来自在K/T(白垩纪和古近纪)地质界线上发现的铱元素(iridium)异常和冲击石英。科学家推测，这种高含量的铱元素就是撞击地球的小行星带来的，冲击石英是在撞击过程中形成的。
正在发生的第六次大灭绝
第六次物种大灭绝，是现代人类真正经历的第一次物种大灭绝。
现在，由于人类活动造成的影响，物种灭绝速度比自然灭绝速度快了1000倍，地球正在进入第六次大灭绝时期。
到21世纪末，预计全球变暖会导致1/2的植物面临生存威胁，超过2/3的维管植物可能完全消失。
托福阅读材料：Swimming Machines
Tunas, mackerels, and billfishes (marlins, sailfishes, and swordfish) swim continuously. Feeding, courtship, reproduction, and even "rest" are carried out while in constant motion. As a result, practically every aspect of the body form and function of these swimming "machines" is adapted to enhance their ability to swim. Many of the adaptations of these fishes serve to reduce water resistance (drag).
Interestingly enough, several of these hydrodynamic adaptations resemble features designed to improve the aerodynamics of high-speed aircraft. Though human engineers are new to the game, tunas and their relatives evolved their "high-tech" designs long ago. Tunas, mackerels, and billfishes have made streamlining into an art form. Their bodies are sleek and compact. The body shapes of tunas, in fact, are nearly ideal from an engineering point of view. Most species lack scales over most of the body, making it smooth and slippery. The eyes lie flush with the body and do not protrude at all. They are also covered with a slick, transparent lid that reduces drag. The fins are stiff, smooth, and narrow, qualities that also help cut drag. When not in use, the fins are tucked into special grooves or depressions so that they lie flush with the body and do not break up its smooth contours. Airplanes retract their landing gear while in flight for the same reason.
Tunas, mackerels, and billfishes have even more sophisticated adaptations than these to improve their hydrodynamics. The long bill of marlins, sailfishes, and swordfish probably helps them slip through the water. Many supersonic aircraft have a similar needle at the nose.
Most tunas and billfishes have a series of keels and finlets near the tail. Although most of their scales have been lost, tunas and mackerels retain a patch of coarse scales near the head called the corselet. The keels, finlets, and corselet help direct the flow of water over the body surface in such as way as to reduce resistance (see the figure). Again, supersonic jets have similar features.
Because they are always swimming, tunas simply have to open their mouths and water is forced in and over their gills. Accordingly, they have lost most of the muscles that other fishes use to suck in water and push it past the gills. In fact, tunas must swim to breathe. They must also keep swimming to keep from sinking, since most have largely or completely lost the swim bladder, the gas-filled sac that helps most other fish remain buoyant.
One potential problem is that opening the mouth to breathe detracts from the streamlining of these fishes and tends to slow them down. Some species of tuna have specialized grooves in their tongue. It is thought that these grooves help to channel water through the mouth and out the gill slits, thereby reducing water resistance.There are adaptations that increase the amount of forward thrust as well as those that reduce drag. Again, these fishes are the envy of engineers. Their high, narrow tails with sweptback tips are almost perfectly adapted to provide propulsion with the least possible effort.
Perhaps most important of all to these and other fast swimmers is their ability to sense and make use of swirls and eddies (circular currents) in the water. They can glide past eddies that would slow them down and then gain extra thrust by "pushing off" the eddies. Scientists and engineers are beginning to study this ability of fishes in the hope of designing more efficient propulsion systems for ships.
The muscles of these fishes and the mechanism that maintains a warm body temperature are also highly efficient. A bluefin tuna in water of 7°C (45°F) can maintain a core temperature of over 25°C (77"F). This warm body temperature may help not only the muscles to workbetter, but also the brain and the eyes. The billfishes have gone one step further. They have evolved special "heaters" of modified muscle tissue that warm the eyes and brain, maintaining peak performance of these critical organs.
Paragraph 1: Tunas, mackerels, and billfishes (marlins, sailfishes, and swordfish) swim continuously. Feeding, courtship, reproduction, and even "rest" are carried out while in constant motion. As a result, practically every aspect of the body form and function of these swimming "machines" is adapted to enhance their ability to swim.
1. The word enhance in the passage is closest in meaning to
○Use
○Improve
○Counteract
○Balance
Paragraph 3: Tunas, mackerels, and billfishes have made streamlining into an art form. Their bodies are sleek and compact. The body shapes of tunas, in fact, are nearly ideal from an engineering point of view. Most species lack scales over most of the body, making it smooth and slippery. The eyes lie flush with the body and do not protrude at all. They are also covered with a slick, transparent lid that reduces drag. The fins are stiff, smooth, and narrow, qualities that also help cut drag. When not in use, the fins are tucked into special grooves or depressions so that they lie flush with the body and do not break up its smooth contours. Airplanes retract their landing gear while in flight for the same reason.
托福阅读材料：生活中有意思的真相
1 Men are 6 times more likely to be struck by lightning than women.
男人被闪电击中的概率比女人高5倍。
2 Over 2500 left handed people a year are killed from using products made for right handed people.
每年有超过2500名左撇子在使用为右撇子设计的产品时死亡。
3 Every time you lick a stamp, you're consuming 1/10 of a calorie.
每次你舔邮票的背面时，你就吃下了1/10个卡路里。
4 Most lipstick contains fish scales.
绝大部分的唇膏里都含有鱼鳞成分。
5 A sneeze travels out your mouth at over 100 m.p.h..
人打喷嚏时，嘴里的气流速度超过每小时100英里。
6 More people use blue toothbrushes, than red ones.
用蓝色牙刷的人比用红色的人多。
7 The most used letter in the English alphabet is "E", and "Q" is the least used.
在英语字母表中，“E”是用得最多的字母，“Q”则是被用得最少的。
8 Every 45 seconds, a house catches on fire in the United States.
在美国，每45秒就有一所房子着火。
9 One in every 4 Americans has appeared on television.
每4个美国人中，就有一个人上过电视。
10 One quarter of the bones in your body are in your feet.
人体内的骨头有1/4集中在双脚上。
11 Human teeth are almost as hard as rocks.
人的牙齿几乎和石头一样硬。
12 The first product to have a bar code was Wrigleys gum.
世界上最早有条形码标记的商品是箭牌香口胶。
13 No piece of square dry paper can be folded more than 7 times in half.
任何一张干燥的方型纸片都不能被对折超过7次以上。
14 Ancient Egyptians slept on pillows made of stone.
古代埃及人的枕头是石头做成的。
15 The average person has over 1,460 dreams a year.
一个普通人每年要做1460个梦。
16 A cockroach can live several weeks with its head cut off--it dies from starvation.
蟑螂在被砍头之后还能活几个星期，最后死也是饿死。
17 Dogs and cats, like humans, are either right or left handed.
猫狗和人一样也有左、右撇子之分。
18 The elephant is the only mammal that can't jump.
大象是唯一一种不会跳的哺乳类动物。
19 Dolphins sleep with one eye open.
海豚睡觉睁一眼闭一眼。
20 The placement of a donkey's eyes in its head enables it to see all four feet at all times.
驴子眼睛的位置能让它随时看到自己的四条腿。
21 The longest recorded flight of a chicken is 13 seconds.
鸡的最长飞行纪录是13秒。
22 Cat urine glows under a black-light.
猫尿能在黑光灯下发光。 更多信息请访问：http://www.24en.com/
23 Over 10,000 birds a year die from smashing into windows.
每年有超过一万只鸟因为撞到窗户上死亡。
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