托福閱讀生物爆發(fā)與滅絕的知識(shí)內(nèi)容
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托福閱讀生物爆發(fā)與滅絕的知識(shí)內(nèi)容
我們一共經(jīng)歷了一次大爆發(fā)，和五次大滅絕。但大家也要知道，我們現(xiàn)在正在經(jīng)歷第六次物種大滅絕。
寒武紀(jì)大爆發(fā)(Cambrian explosion)——5.4億年前
奧陶紀(jì)大滅絕(Ordovician extinction)——4.4億年前
泥盆紀(jì)大滅絕(Devonian extinction)——3.65億年前
二疊紀(jì)大滅絕(Permian extinction)——2.5億年前
三疊紀(jì)大滅絕(Triassic extinction)——2億年前
白堊紀(jì)大滅絕(Cretaceous extinction)——6500萬年前
寒武紀(jì)大爆發(fā)
寒武紀(jì)大爆發(fā)(Cambrian explosion)被稱為古生物學(xué)和地質(zhì)學(xué)上的一大懸案!自達(dá)爾文以來就一直困擾著進(jìn)化論等學(xué)術(shù)界。
大約5億4200萬年前到5億3000萬年前，在地質(zhì)學(xué)上稱作寒武紀(jì)的開始，絕大多數(shù)無脊椎動(dòng)物(invertebrate)在這2000多萬年時(shí)間內(nèi)出現(xiàn)。
這種幾乎是“同時(shí)地”、“突然地”在2000多萬年時(shí)間內(nèi)出現(xiàn)在寒武紀(jì)地層中的無脊椎動(dòng)物化石(節(jié)肢動(dòng)物arthropod、軟體動(dòng)物、環(huán)節(jié)動(dòng)物等)，而在寒武紀(jì)之前更為古老的地層中長(zhǎng)期以來卻找不到動(dòng)物化石的現(xiàn)象，被古生物學(xué)家稱作“寒武紀(jì)生命大爆發(fā)”，簡(jiǎn)稱“寒武紀(jì)爆發(fā)”。
這也是顯生宙(Phanerozoic eon)的開始
100多年以來，有兩種基本觀點(diǎn)
一種觀點(diǎn)認(rèn)為，寒武爆發(fā)是一種假象，這是某些達(dá)爾文或新達(dá)爾文主義(Darwinism)者所支持的觀點(diǎn)。
由于進(jìn)化是漸進(jìn)的，所謂“爆發(fā)”只是表明首次在生物化石記錄中發(fā)現(xiàn)了早在前寒武紀(jì)就已經(jīng)廣泛存在并發(fā)展的生物，其他的生物化石群可能是由于地質(zhì)記錄的不完全而“缺檔”。
造成這種“缺檔”的原因是前寒武紀(jì)地層(stratum)經(jīng)歷著熱與壓力，其中的化石被銷毀了。
由于發(fā)現(xiàn)錢寒武紀(jì)化石沉積層(sedimentary formation)中存在大量細(xì)菌(bacteria)和藍(lán)藻(blue-algae)這樣的原核生物(prokaryotic organism)，因而這一解釋不再有說服力。
另一種觀點(diǎn)認(rèn)為，寒武紀(jì)爆發(fā)代表了生物進(jìn)化過程中的真實(shí)事件名科學(xué)家從物理環(huán)境和生態(tài)環(huán)境的變化兩個(gè)方面來解釋這一現(xiàn)象。
1965年，兩位美國(guó)物理學(xué)家提出了寒武紀(jì)爆發(fā)是由于地球大氣的氧水平(atmospheric)這個(gè)物理原因造成的。
他們認(rèn)為，在早期地球的大氣中含有很少或根本沒有自由氧，氧是前寒武紀(jì)(Precambrianperiod)藻類植物光合作用(photosynthesis)的產(chǎn)物并逐漸積累(accumulation)形成的。
后生動(dòng)物需要大量的氧，一方面用于呼吸作用(respiration)，另一方面氧還以臭氧(ozonic)的形式在大氣中吸收大量有害的紫外線(ultraviolet ray)，使后生動(dòng)物免于有害輻射的損傷。
生物大滅絕
生物大滅絕(Biological extinction)是指大規(guī)模的集群滅絕，生物滅絕有叫生物絕種。
在集群滅絕(mass extinction)過程中，往往是整個(gè)分類單元中的所有物種，無論在生態(tài)系統(tǒng)中的地位高低，都逃不過劫難(catastrophe)
大規(guī)模的集群滅絕有一定的周期性(periodic)，大約6200萬年就會(huì)發(fā)生一次，但集群滅絕對(duì)動(dòng)物的影響最大，而陸生植物(terrestrialplant)的集群滅絕不像動(dòng)物那樣顯著
奧陶紀(jì)大滅絕
第一次物種大滅絕發(fā)生在4億4千萬年前的奧陶紀(jì)末期(Ordovicianperiod)，由于當(dāng)時(shí)氣候變冷并且海平面下降，生活在水體的各種不同的無脊椎動(dòng)物便蕩然無存
在大約4.4億年前，撒哈拉坐在的陸地曾經(jīng)位于南極(the Antarctic Pole)，當(dāng)陸地匯集在極點(diǎn)附近時(shí)，容易造成厚的積冰。大片的冰川(glacier)使洋流(ocean current)和大氣環(huán)流(generalatmospheric circulation)變冷，整個(gè)地球的溫度下降，冰川鎖住水，海平面降低，原先豐富的沿海生態(tài)系統(tǒng)被破壞，導(dǎo)致85%的物種滅絕。
泥盆紀(jì)大滅絕
第二次物種大滅絕發(fā)生在泥盆紀(jì)晚期(Devonian)，其原因也是地球氣候變冷河海洋退卻。
在距今3.65億年前的泥盆紀(jì)后期，經(jīng)歷了兩個(gè)高峰，中間間隔100萬年，發(fā)生地球史上第二次物種滅絕事件，海洋生物遭到重創(chuàng)。
二疊紀(jì)大滅絕
第三次物種大滅絕發(fā)生在距今2.5億年前的二疊紀(jì)末期(Permian)，發(fā)生了有史以來最嚴(yán)重的大滅絕事件，估計(jì)地球上有96%的物種滅絕，其中90%的海洋生物和70%的陸地脊椎動(dòng)物滅絕。重要珊瑚(coral)群全部消失。
這次大滅絕使得生態(tài)系統(tǒng)獲得了一次最徹底的更新，為恐龍等爬行類動(dòng)物(reptile)的進(jìn)化鋪平了道路。
這一次大滅絕是地球歷史上從古生代(Paleozoic)向中生代(Mesozoic)轉(zhuǎn)折的里程碑。
在二疊紀(jì)曾經(jīng)發(fā)生海平面下降和大陸漂移(continental drift)，造成了最嚴(yán)重的物種大滅絕。所有的大陸聚集成了一個(gè)聯(lián)合的盤古大陸(archicontinent)，海岸線急劇減少，大陸架(continental shelf)也縮小了，很多生物失去了生存空間。
更嚴(yán)重的是，當(dāng)淺層的大陸架暴露出來后，原先埋藏在海底的有機(jī)質(zhì)(organic matter)被氧化(oxidization)，這個(gè)過程消耗了氧氣，釋放出二氧化碳(carbon dioxide)，大氣中氧含量減少對(duì)陸地生物的生存造成了巨大的傷害。
三疊紀(jì)大滅絕
第四次物種大滅絕發(fā)生在距今1.95億年前的三疊紀(jì)末期(Triassic period)，有76%的物種滅絕，其中主要為海洋生物，這次大滅絕并無明顯的標(biāo)志，只發(fā)現(xiàn)海平面下降之后又上升，出現(xiàn)大面積缺氧的海水。
白堊紀(jì)大滅絕
科學(xué)家們推斷第五次物種大滅絕是由小行星撞擊而發(fā)生的，這次撞擊相當(dāng)于人類歷史上發(fā)生過最強(qiáng)烈地震(seismic)的100萬倍，爆炸的能量相當(dāng)于地球上核武器總量爆炸的1萬倍，導(dǎo)致了2.1萬立方公里的物質(zhì)進(jìn)入大氣中。
由于大氣中大量高密度(high-density)的塵埃，太陽光不能照射到地球上，導(dǎo)致地球表面溫度迅速降低。
沒有陽光，植物逐漸枯萎(withered)死亡;沒有植物，植食性(phytophagous)的恐龍饑餓而死;沒有植食性動(dòng)物，肉食性(sarcophagy)的恐龍失去食物來源，在絕望和相互殺戮中緩慢消亡。
幾乎所有的大型陸生動(dòng)物都未能幸免于難。小型的陸生動(dòng)物(terrestrial animal)，像一些哺乳動(dòng)物(mammal)依靠殘余的食物勉強(qiáng)為生，終于熬過了最艱難的日子，等到了古近紀(jì)(Paleogene)陸生脊椎動(dòng)物迎來了再次的大繁榮。
撞擊假說的支持者發(fā)現(xiàn)了許多有力的證據(jù)。最有力的證據(jù)來自在K/T(白堊紀(jì)和古近紀(jì))地質(zhì)界線上發(fā)現(xiàn)的銥元素(iridium)異常和沖擊石英?？茖W(xué)家推測(cè)，這種高含量的銥元素就是撞擊地球的小行星帶來的，沖擊石英是在撞擊過程中形成的。
正在發(fā)生的第六次大滅絕
第六次物種大滅絕，是現(xiàn)代人類真正經(jīng)歷的第一次物種大滅絕。
現(xiàn)在，由于人類活動(dòng)造成的影響，物種滅絕速度比自然滅絕速度快了1000倍，地球正在進(jìn)入第六次大滅絕時(shí)期。
到21世紀(jì)末，預(yù)計(jì)全球變暖會(huì)導(dǎo)致1/2的植物面臨生存威脅，超過2/3的維管植物可能完全消失。
托福閱讀材料：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
○B(yǎng)alance
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.
托福閱讀材料：生活中有意思的真相
1 Men are 6 times more likely to be struck by lightning than women.
男人被閃電擊中的概率比女人高5倍。
2 Over 2500 left handed people a year are killed from using products made for right handed people.
每年有超過2500名左撇子在使用為右撇子設(shè)計(jì)的產(chǎn)品時(shí)死亡。
3 Every time you lick a stamp, you're consuming 1/10 of a calorie.
每次你舔郵票的背面時(shí)，你就吃下了1/10個(gè)卡路里。
4 Most lipstick contains fish scales.
絕大部分的唇膏里都含有魚鱗成分。
5 A sneeze travels out your mouth at over 100 m.p.h..
人打噴嚏時(shí)，嘴里的氣流速度超過每小時(shí)100英里。
6 More people use blue toothbrushes, than red ones.
用藍(lán)色牙刷的人比用紅色的人多。
7 The most used letter in the English alphabet is "E", and "Q" is the least used.
在英語字母表中，“E”是用得最多的字母，“Q”則是被用得最少的。
8 Every 45 seconds, a house catches on fire in the United States.
在美國(guó)，每45秒就有一所房子著火。
9 One in every 4 Americans has appeared on television.
每4個(gè)美國(guó)人中，就有一個(gè)人上過電視。
10 One quarter of the bones in your body are in your feet.
人體內(nèi)的骨頭有1/4集中在雙腳上。
11 Human teeth are almost as hard as rocks.
人的牙齒幾乎和石頭一樣硬。
12 The first product to have a bar code was Wrigleys gum.
世界上最早有條形碼標(biāo)記的商品是箭牌香口膠。
13 No piece of square dry paper can be folded more than 7 times in half.
任何一張干燥的方型紙片都不能被對(duì)折超過7次以上。
14 Ancient Egyptians slept on pillows made of stone.
古代埃及人的枕頭是石頭做成的。
15 The average person has over 1,460 dreams a year.
一個(gè)普通人每年要做1460個(gè)夢(mèng)。
16 A cockroach can live several weeks with its head cut off--it dies from starvation.
蟑螂在被砍頭之后還能活幾個(gè)星期，最后死也是餓死。
17 Dogs and cats, like humans, are either right or left handed.
貓狗和人一樣也有左、右撇子之分。
18 The elephant is the only mammal that can't jump.
大象是唯一一種不會(huì)跳的哺乳類動(dòng)物。
19 Dolphins sleep with one eye open.
海豚睡覺睜一眼閉一眼。
20 The placement of a donkey's eyes in its head enables it to see all four feet at all times.
驢子眼睛的位置能讓它隨時(shí)看到自己的四條腿。
21 The longest recorded flight of a chicken is 13 seconds.
雞的最長(zhǎng)飛行紀(jì)錄是13秒。
22 Cat urine glows under a black-light.
貓尿能在黑光燈下發(fā)光。 更多信息請(qǐng)?jiān)L問：http://www.24en.com/
23 Over 10,000 birds a year die from smashing into windows.
每年有超過一萬只鳥因?yàn)樽驳酱皯羯纤劳觥?/p>
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