关于恐龙灭绝的未解之谜的英文文章

中英都有
The extinction of dinosaurs
The mystery of dinosaur extinction
More than 200,000,000 years ago in the Mesozoic, a large number of reptiles living on land, it is also known as the Mesozoic "era of reptiles," the earth was the first to occupy a wide range of vertebrates. At that time the Earth's climate was warmer, all over the dense forests, reptiles have enough food, gradually prospered, more and more species. They continued to differentiate into a variety of different types of reptiles, some of today has become a turtle, and some turned into the type of crocodile, and some turned into today's snakes and lizards, which are a class of Around the world and evolved into today's mammals.
All is the dinosaur reptiles in the largest class of physical, very suitable for living in the marshes and shallow lake, when warm, humid air, food is also very easy to find. Therefore, dinosaurs ruled the earth for several million years of time, but I do not know why, in their 6500 years ago a very short period of time of the extinction of a sudden, people see only the left by that time a large number of dinosaur fossils.
With regard to the reasons for the extinction of dinosaurs, it is still being studied. For a long time, the most authoritative view, and the extinction of the dinosaurs 6500 years ago about a large meteorite. According to the study, there was a 7-10 km in diameter asteroid will fall on the earth's surface, causing a large explosion, such as throwing a lot of dust in the atmosphere to form the Zhetianbiri House of Sand and Fog, led to the suspension of plant photosynthesis , And therefore the extinction of the dinosaurs.
Asteroid impact theory quickly gained the support of many scientists. In 1991, in Mexico's Yucatan Peninsula occurred in the discovery of a long period of the meteorite impact craters, the fact is further evidence of this point of view. Today, this view seems to have become a conclusion.
But there are also many people for such an asteroid impact on the skeptical, because the fact is: frogs, crocodiles and many other very sensitive to the temperature of the animals have resisted and survived the Cretaceous. This theory can not explain why only the dinosaurs died. To date, scientists have put forward for the cause of the extinction of dinosaurs have been no fewer than a dozen scenarios, more wealth to the dramatic and exciting, "said the meteorite collision," but it is one of them.
In addition to the "meteorite collision", the extinction of dinosaurs on the main point of view there are the following:
First, climate change, said. 6500 million years ago, the Earth's climate suddenly changes in the temperature dropped, resulting in decreased oxygen in the atmosphere so that the dinosaurs could not survive. It was also suggested that dinosaurs are cold-blooded, but with no hair or warm organ and can not adapt to the Earth's temperature dropped, were frozen to death of.
Second, the species, said the fight. End of the dinosaur era, first appeared in small mammals, these animals are rodent predators may feed to eggs. As a result of this lack of small animal predators, more and more and eventually eat up the eggs.
Third, continental drift, said. Geology Research shows that the survival of dinosaurs at the age of the Earth's only a piece of the mainland only, that is, "Pangea." Due to changes in the earth's crust, the continent took place in the Jurassic of the larger division and drift, leading to the environment and climate change, and therefore the extinction of dinosaurs.
Fourth, changes in the geomagnetic said. Modern biology shows that certain biological and magnetic fields related to the death. More sensitive to the magnetic field of biology, in the Earth's magnetic field changes, may lead to extinction. It seems therefore that the extinction of the dinosaurs may be related to changes in the Earth's magnetic field.
V. said angiosperm poisoning. End of the dinosaur era, the Earth gymnosperms gradually disappearing, replaced by a large number of angiosperms, gymnosperms contain these plants are not in toxic shape of a huge dinosaur odd food, intake of angiosperms led to the accumulation of toxins in the body over , Has been the poison.
Six, said acid rain. The late Cretaceous period may have been under strong acid rain, soil, including in the trace element strontium, be dissolved dinosaurs through drinking water and food, directly or indirectly, strontium intake, acute or chronic poisoning, the last groups of the dead.
In Mexico's Yucatan peninsula have called the Chicxulub crater (Chicxulub Crater), and its 6,500 years ago What is the relationship between the extinction of dinosaurs? The answer on the hidden message in this layer of rock where.
This layer of rock known as the KT boundary by geologists (KT boundary), is the meaning of the Cretaceous - Tertiary marking the limits of the line. The lower rocks rich in dinosaur fossils, but in the KT boundary over the disappearance of the dinosaurs.
KT boundary in rocks containing iridium, a rare metal iridium in the earth in an average of only a billionth of content. However, the content of iridium in the rock formation is 200 times the normal concentration. Where can find so many Iridium do? In space.
The content of iridium in space than on Earth thousands of times higher than 1. It was also a white layer of rock found evidence of the impact of quartz, the asteroid will only leave such a mark. High levels of iridium and the impact of quartz, appear in many parts of the earth's Tertiary Boundary in rock. This global mark may only be the most severe impact. Impact on the location of Mexico is still in the Yucatan Peninsula.
6 million years ago, this very severe impact, in the history of mankind and in any event could not live up to it than that. Then hit the Earth asteroid or comet, the width is about 6 miles. It is more than 40 times the speed of sound into the Earth's surface. It's a very large volume, so when it hit the Earth, the front-end has encountered the surface, the rear still 30,005 of the 1000 feet high, equivalent to the jet's altitude. Colliding with Earth is the size of the mountain like a rock.
The reasons for the extinction of dinosaurs on the hypothesis that the above-mentioned far more than these. But these above-mentioned hypothesis in the scientific community has more supporters. Of course, each of the above, there is an imperfect place. For example, "climate change" does not clarify the causes of climate change. After inspection, some small dinosaurs in the Coelurosauria, with enough early against small mammals, so "species struggle to say" there are loopholes. In modern geology, the "continental drift theory" itself is still a hypothesis. "Angiosperms poisoning" and "acid rain" the same lack of sufficient evidence. As a result, the real cause of the extinction of dinosaurs, have yet to explore it further.
In our planet, there was a lot of species appear and then disappear, it is a biological evolution in the history of a natural stage. But as such a huge dinosaur-dominated family, why all of a sudden the vanish from the earth, and this can not but arouse our speculation. At the end of the Cretaceous period 6500 years ago, what makes a large number of dinosaurs and other biological all dead, scientists have been debating. Some said that the Earth at that time took place on the geological orogeny, as many grown on the plains to the mountains, marshes will be reduced, the climate has become less a warm and humid. The dinosaurs can not meet the respiratory dry and hot dry and cold air, and one winter, the dinosaur's food is gone, so have reached an impasse. Some said that the supernova caused by the outbreak of the Earth's climate changes in a strong, sudden temperature rise and then fall very low because of. There are said to be dinosaurs of ate a lot of flowering plants, which have spent a lot of toxins, food and a large dinosaur, the poisoning death. Is evidence that when flowering plants appeared. It was also said to try to be different because of the huge dinosaurs such animals as a result of eating too much and continue to fart, into the air to release a large number of methane gas. As the number of them are too many to survive a long time, the destruction of the Earth's ozone layer caused by the devastating climate. Some people even said to be alien to the Earth went to the outcome of the game, because they feel that the dinosaur meat is especially good. Evidence found in the Arctic is their skeletal fossils of dinosaurs have been like a laser cutting traces. In short, I can be varied, there is not strange. However, we are widely recognized is that the meteorite impact.
In 1980, American scientists in 6500 million years ago found that the formation of a high concentration of iridium, its content more than the normal content of dozens or even hundreds of times. The concentration of iridium in this way can be found in meteorites, the scientists put it linked to the extinction of dinosaurs. According to the content of iridium also estimated the impact object is equal to the diameter of 10 km asteroid. Such a huge meteorite hit the Earth, is an unparalleled blow to the strength of the earthquake to calculate, is about 10 Richter, and the resulting impact crater diameter will be more than 100 km. Scientists took 10 years to finally have the preliminary results, they Yucatan Peninsula in Central America in the strata found in the pit. It is estimated that in the pit of a diameter of 180 km to 300 km. Now, scientists are still in the pit of further study.
Scientists have begun to describe our 6500 years ago that the heroic act. One day, the dinosaurs are still in the carefree paradise on Earth to eat or drink much, the sky suddenly appeared in a dazzling white light, a diameter of 10 kilometers is equivalent to a medium-sized city as large boulders appear out of the blue. It was an asteroid, it is 40 kilometers per second speed crashed into a sea off the seabed in a huge deep sea water has been rapid gasification, steam injection to the high tens of thousands of meters, then set off the tsunami of up to 5 km, and in order to speed the spread of water into the ground all across the land, the surging waves swept across the earth's surface after the rendezvous point on the impact of the back end, where the enormous power of water led to a strong volcanic Deccan Plateau Eruption at the same time so that the earth's plate movement direction has changed.
It was a terrible disaster, how ah. Meteorite impacts on Earth have had extensive dust, polar melting snow, the destruction of the plant, the sky is full of volcanic ash. A dark time, a sharp fall in temperatures, heavy rainfall, flash floods, landslides swept away the dinosaurs and will be buried together. Over the next few months and even years, the sky is still rolling cloud of dust, clouds, but not throughout the year as a result of the Earth and the sun into the cold, vast land of a quiet time for silent. An era in the history of biotechnology on such an end.
Whether these things really happened, all the dinosaur extinction would be a strange thing. Fortunately, we have received a number of valuable dinosaur fossils, so scientists can conduct research. We hope that in the near future, this will certainly solve the mystery. At the same time we should be aware that any of the biological have to go through, prosperity, the demise of the process. This is a law of nature, and that species will not be huge and powerful change. The extinction of dinosaurs, followed by the emergence of a new era of more advanced biological world to decorate the Earth's even better.
恐龙灭绝
恐龙灭绝之谜
在两亿多年前的中生代,大量的爬行动物在陆地上生活,因此中生代又被称为“爬行动物时代”,大地第一次被脊椎动物广泛占据.那时的地球气候温暖,遍地都是茂密的森林,爬行动物有足够的食物,逐渐繁盛起来,种类越来越多.它们不断的分化成各种不同种类的爬行动物,有的变成了今天的龟类,有的变成了今天的鳄类,有的变成了今天的蛇类和蜥蜴类,其中还有一类演变成今天遍及世界的哺乳动物.
恐龙是所有爬行动物中体格最大的一类,很适宜生活在沼泽地带和浅水湖里,那时的空气温暖而潮湿,食物也很容易找到.所以恐龙在地球上统治了几千万年的时间,但不知什么原因,它们在6500万年前很短的一段时间内突然灭绝了,今天人们看到的只是那时留下的大批恐龙化石.
关于恐龙灭绝的原因,人们仍在不断地研究之中.长期以来,最权威的观点认为,恐龙的灭绝和6500万年前的一颗大陨星有关.据研究,当时曾有一颗直径7-10公里的小行星坠落在地球表面,引起一场大爆炸,把大量的尘埃抛如大气层,形成遮天蔽日的尘雾,导致植物的光合作用暂时停止,恐龙因此而灭绝了.
小行星撞击理论,很快获得了许多科学家的支持.1991年,在墨西哥的尤卡坦半岛发现一个发生在久远年代的陨星撞击坑,这个事实进一步证实了这种观点.今天,这种观点似乎已成定论了.
但也有许多人对这种小行星撞击论持怀疑态度,因为事实是：蛙类、鳄鱼以及其他许多对气温很敏感的动物都顶住了白垩纪而生存下来了.这种理论无法解释为什么只有恐龙死光了.迄今为止,科学家们提出的对于恐龙灭绝原因的假想已不下十几种,比较富于刺激性和戏剧性的“陨星碰撞说”不过是其中之一而已.
除了“陨星碰撞说”以外,关于恐龙灭绝的主要观点还有以下几种：
一、气候变迁说.6500万年前,地球气候陡然变化,气温大幅下降,造成大气含氧量下降,令恐龙无法生存.也有人认为,恐龙是冷血动物,身上没有毛或保暖器官,无法适应地球气温的下降,都被冻死了.
二、物种斗争说.恐龙年代末期,最初的小型哺乳类动物出现了,这些动物属啮齿类食肉动物,可能以恐龙蛋为食.由于这种小型动物缺乏天敌,越来越多,最终吃光了恐龙蛋.
三、大陆漂移说.地质学研究证明,在恐龙生存的年代地球的大陆只有唯一一块,即“泛古陆”.由于地壳变化,这块大陆在侏罗纪发生的较大的分裂和漂移现象,最终导致环境和气候的变化,恐龙因此而灭绝.
四、地磁变化说.现代生物学证明,某些生物的死亡与磁场有关.对磁场比较敏感的生物,在地球磁场发生变化的时候,都可能导致灭绝.由此推论,恐龙的灭绝可能与地球磁场的变化有关.
五、被子植物中毒说.恐龙年代末期,地球上的裸子植物逐渐消亡,取而代之的是大量的被子植物,这些植物中含有裸子植物中所没有的毒素,形体巨大的恐龙食量奇大,摄入被子植物导致体内毒素积累过多,终于被毒死了.
六、酸雨说.白垩纪末期可能下过强烈的酸雨,使土壤中包括锶在内的微量元素被溶解,恐龙通过饮水和食物直接或间接地摄入锶,出现急性或慢性中毒,最后一批批死掉了.
在墨西哥的尤卡坦半岛上有一个叫做希克苏鲁伯的陨石坑（Chicxulub Crater）,它和6500万年前的恐龙灭绝有什么关系?答案就隐藏在这层白白的岩石里.
这层岩石被地质学家称为K-T边界（K-T boundary）,意思是白垩纪-第三纪界限的标记线.下层岩石中含有丰富的恐龙化石,但在K-T边界以上,恐龙消失了.
K-T边界岩石中含有铱,铱是一种稀有金属,在地球中的平均含量只有十亿分之一.然而这个岩层中的铱含量是正常含量的200倍.还能在哪里找到这么多的铱呢?在太空中.
太空中的铱含量比地球高出1千倍.人们还在这层白色岩石中找到了冲击石英的证据,只有小行星才会留下这样的标记.高含量的铱和冲击石英,出现在地球上许多地方的第三纪界限岩层里.这种全球性的痕迹,只可能来自最猛烈的撞击.撞击的地点就在现在墨西哥的犹卡坦半岛.
6千5百万年前的这次撞击非常猛烈,人类历史上的任何事件都没法和它比.那时撞上地球的小行星或彗星,宽度大约是6英里.它以超过40倍音速的速度冲向地球表面.它的体积非常庞大,所以当它撞上地球时,前端已经碰到了地表,尾部却还在3万5千英尺的高空,相当于喷气式客机的飞行高度.撞击地球的是高山一样大小的一块巨岩.
关于恐龙灭绝原因的假说,远不止上述这几种.但是上述这几种假说,在科学界都有较多的支持者.当然,上面的每一种说法都存在不完善的地方.例如,“气候变迁说”并未阐明气候变化的原因.经考察,恐龙中某些小型的虚骨龙,足以同早期的小型哺乳动物相抗衡,因此“物种斗争说”也存在漏洞.而在现代地质学中,“大陆漂移学说”本身仍然是一个假说.“被子植物中毒说”和“酸雨说”同样缺乏足够的证据.因此,恐龙灭绝的真正原因,还有待于人们的进一步探究.
在我们的地球上,曾经有很多生物种类出现后又消失了,这是一个生物演化史中的必然阶段.但是像恐龙这样一个庞大的占统治地位的家族,为什么会突然之间就从地球上消失了,这不能不引起我们的种种猜测.在6500万年前白垩纪结束的时候,究竟发生了什么,使得恐龙和另外一大批生物统统死去,科学家们对此一直争论不休.有的说是地球在那个时候发生了地质上的造山运动,因为平地上长出许多高山来,沼泽便减少了,气候也变得不那么湿润温暖了.恐龙的呼吸器官不能适应干冷干热的空气,而且一到冬天,恐龙的食物也没有了,所以就走上了绝路.有的说是超新星爆发引起地球气候发生强烈变化,温度骤然升高后又降得很低的缘故.还有的说是恐龙吃了大量的有花植物,这些花中有很多毒素,恐龙又食量很大,所以中毒而死.证据是那个时候开始出现了有花植物.还有人别出心裁地说,是因为恐龙这种巨大的动物因吃的太多且不断放屁,向空中释放大量的甲烷气体.由于它们数量太多,生存时间又长,所以破坏了地球的臭氧层造成毁灭性气候.甚至还有人说是外星人跑到地球来猎取的结果,因为它们觉得恐龙肉特别好吃.证据是他们在北极发现的恐龙骨胳化石有像被激光切割的痕迹.总之,真可谓是五花八门,无奇不有.但是,普遍被大家认可的是陨石撞击说.
1980年,美国科学家在6500万年前的地层中发现了高浓度的铱,其含量超过正常含量几十甚至数百倍.这样浓度的铱在陨石中可以找到,因此,科学家们就把它与恐龙灭绝联系起来了.根据铱的含量还推算出撞击物体是相当于直径10公里的一颗小行星.这么大的陨石撞击地球,绝对是一次无与伦比的打击,以地震的强度来计算,大约是里氏10级,而撞击产生的陨石坑直径将超过100公里.科学工作者用了10年的时间,终于有了初步结果,他们在中美洲犹加敦半岛的地层中找到了这个大坑.据推算,这个坑的直径在180公里到300公里之间.现在,科学工作者们还在对这个大坑做进一步的研究.
科学家们开始为我们描绘6500万年前那壮烈的一幕.有一天,恐龙们还在地球乐园中无忧无虑地尽情吃喝,突然天空中出现了一道刺眼的白光,一颗直径10公里相当于一座中等城市般大的巨石从天而降.那是一颗小行星,它以每秒40公里的速度一头撞进大海,在海底撞出一个巨大的深坑,海水被迅速气化,蒸气向高空喷射达数万米,随即掀起的海啸高达5公里,并以极快的速度扩散,冲天大水横扫着陆地上的一切,汹涌的巨浪席卷地球表面后会合于撞击点的背面一端,在那里巨大的海水力量引发了德干高原强烈的火山喷发,同时使地球板块的运动方向发生了改变.
那是一场多么可怕的灾难啊.陨石撞击地球产生了铺天盖地灰尘,极地雪融化,植物毁灭了,火山灰也充满天空.一时间暗无天日,气温骤降,大雨滂沱,山洪暴发,泥石流将恐龙卷走并埋葬起来.在以后的数月乃至数年里,天空依然尘烟翻滚,乌云密布,地球因终年不见阳光而进入低温中,苍茫大地一时间沉寂无声.生物史上的一个时代就这样结束了.
不论以上的事情是否真的发生过,恐龙的全部灭绝都将是一个奇特的事情.好在我们现在获得了一些珍贵的恐龙化石,使科学家们的研究工作能够进行.我们希望不久的将来,这个谜一定会解开.同时我们应该知道,任何一种生物都要经历产生、繁荣、灭亡的过程.这是大自然的规律,并不会因为那一物种庞大强盛而改变.恐龙灭绝了,随后出现了一个崭新的时代,更多的更高级的生物世界把地球装点得更加美好.