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生物历史上的千古之谜！恐龙是怎么灭绝的？
　　现在我们知道，恐龙灭绝的时间是在距今约6500万年前，在那个时候，不仅统治了地球达1亿多年的各种恐龙全部绝灭了，在这次灾难中灭绝的还有鱼龙、蛇颈龙等海洋爬行动物，翼龙等会飞的爬行动物，彩蜥等恐龙的陆生爬行动物亲戚，菊石、箭石等海洋无脊椎动物，海洋中的微型浮游动植物，如钙质浮游有孔虫和钙质微型浮游植物等也几乎被一扫而光。经过这场大劫难，当时地球上大约50%的生物属和几乎75%的生物种从地球上永远消失了。
　　一种假说认为，恐龙禁不起白垩纪晚期的寒冷气候而导致无法存活。有论点称，恐龙是温血动物，它们具有相对较高的代谢速率，有可能维持一定的体温。可是恐龙的呼吸器官并不完善，不能充分补给氧。这就导致恐龙体温并不高，可能接近现代树懒。而由于恐龙庞大的躯体，想维持这样的体温，只能生存在热带气候区。如果体温降到一定的范围之下，温血动物就要消耗体能以提高体温，否则就需要保温。恐龙过于庞大的身躯，不能进入洞中避寒，如果寒冷的日子持续几天，可能就会因为耗尽体力而遭到冻死的命运。但是，这种学说有一个疑点，那就是恐龙不都是那么庞大的，不一定都不能躲进洞里避难，所以这种学说也有不完善的地方，也需要修正。
恐龙灭绝的假想图
　　另一种假说认为，恐龙灭绝于小行星的撞击。科研团队在6534.83万年前的希克苏鲁伯陨石坑K－T线地层中发现了高浓度的铱，其含量超过正常含量二百三十二倍，如此高浓度的铱只有在太空中的陨石中才可以找到，地球本身是不可能存在的。根据墨西哥湾周围铱元素含量的精确测定，当时是一颗相当于珠穆朗玛峰的小行星的物质不仅撞击了地球中美洲地区，还撞破了地壳，地球因此停转0.2毫秒，然后是地球上从来没有发生过的大地震。撞击使熔浆被抛到数千米的高空，继而是长达几十天的流火现象。高温也许不是最致命的，数以千万吨的灰尘、有毒物质在随后的一个月内遍及全球。在以后的四个多月里，太阳只是一个模糊的影子，植物停止了生长，食草动物大量减少，污浊的空气、短缺的食物、肆意的疾病等等无不摧残着幸存下来的恐龙。由于尘土的遮盖，地球上面临着寒冷的侵袭，但寒冷似乎不是最严重的问题，但是，请记住一些动物的性别是由温度决定的，恐龙也许正是其中之一。
在睡眠时被永远固定的恐龙――寐龙
　　气候骤变造成恐龙绝灭的一条可能的途径是严重影响恐龙的卵。一些科学家发现，在恐龙灭绝之前的白垩纪末期，恐龙蛋的蛋壳有变薄的趋势，说明在恐龙大绝灭之前有气候急剧变化造成的作用。我国的一些古生物学家也发现，在一些化石地点产出的恐龙蛋中，临近绝灭时期的那些恐龙蛋蛋壳上的气孔比其它时期的恐龙蛋蛋壳中的气孔要少，这很可能与气候变得寒冷干燥有关。
恐龙卵化石，可见其中清晰的未孵化胚胎
　　白垩纪末期的恐龙大绝灭是生物历史上的一个千古之谜，科学家们经过不懈的努力，分析研究了到目前为止可以发现的所有线索，提出了一个又一个的理论来试图解释其原因，但是至今，我们都没有一个让所有人都能够接受的定论。
　　也许，这样的答案等待着我们来寻找。
　　注：本文中图片均来自网络素材，有修改
　　作者：中国人民大学附属中学朝阳学校 张霄
　　审稿人： 江建敏
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十万个为什么：恐龙为什么会灭绝?
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十万个为什么：恐龙为什么会灭绝?
对于恐龙的灭绝，人们曾有过种种猜测和探索，我们不妨比较一下，哪种观点更趋于合理。有人认为，7000万年前，比恐龙更.高等的哺乳动物已大量存在，它们对外界环境的适应能力及生活：能力都比恐龙强，尤其是这些哺乳动物常以恐龙蛋为食，在相互的生存竞争中，其他的哺乳动物占了上风，恐龙逐渐走向消亡。
早在2亿年前的中生代，大型爬行动物恐龙曾是地球的主宰，但到了6500万年前，数量众多的恐龙却突然在地球上灭绝了，以至于今天我们所知道的恐龙，只有在古化石中去领略了。
对于恐龙的灭绝，人们曾有过种种猜测和探索，我们不妨比较一下，哪种观点更趋于合理。有人认为，7000万年前，比恐龙更.高等的哺乳动物已大量存在，它们对外界环境的适应能力及生活：能力都比恐龙强，尤其是这些哺乳动物常以恐龙蛋为食，在相互的生存竞争中，其他的哺乳动物占了上风，恐龙逐渐走向消亡。
另一种观点认为，中生代四季长春，气候温暖，适宜恐龙生息繁衍，后来整个地球变冷，恐龙皮肤裸露，没有保暖的羽毛，同时由于脑量太小，行动迟缓，又不能向其他小型爬行动物那样挖洞穴居，冬眠御寒，因此导致了灭绝。
还有人从大陆漂移学说提出，恐龙生存的时代，地球上的大陆还只有一块，气候温和，四季常青。到了侏罗纪，大陆开始发生漂移，导致造山运动、地壳变化和气候的变化，裸子植物逐渐消亡，春花秋落的被子植物成为主导，食物的短缺及气候变冷，使恐龙迅速走向消亡。
也有人提出，在6500万年前，曾有一颗小行星坠落地球，引起大爆炸，使大量的尘埃抛人大气层，形成了遮天蔽日的尘雾，地球上的生态系统遭到破坏，恐龙也随之消失了。关于恐龙灭绝的原因，说法可以说是多种多样，而且站在一定角度看，似乎都有一些道理，但每一个说法严格推敲起来，又都有许多漏洞，都属于假说，因此恐龙的灭绝原因，可能成为一个永久之谜，让人们去无尽的遐想。
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　　【杂志精选】恐龙为什么会灭绝
　　6500万年前（白垩纪末期）发生的一次大灭绝事件，使恐龙等一大批爬行动物灭绝了，同时消亡的还有海洋生物中的菊石、箭石等。这次大灭绝的凶手又是谁呢？
　　凶手是小行星？
　　人们提出了许多假说来试图解释恐龙灭绝的原因，其中最著名的就是美国科学家阿尔瓦雷斯等人提出的“小行星撞击说”。这个假说之所以被很多科学家支持，是因为对意大利、丹麦等许多地域上百个剖面的研究发现，在白垩纪末期黏土层中有含量异常的铱和冲击石英颗粒。由于地球上铱的含量很低，因此异常的铱含量有可能来自于地球外的小行星，而冲击石英颗粒也只有在高温下才可能形成。此外，科学家们在墨西哥的在尤卡坦半岛发现了直径180千米、深900米的巨大陨石坑，说明巨大的撞击是确实发生过的。科学家根据这些证据提出了一种令人兴奋的假说：有一颗直径达10千米的小天体，从天而降，造成了这场大灭绝。
　　可以设想一下，一个直径为10千米的天外来客是一个什么概念呢？地球大气层下部的对流层不过7千米，而大洋的平均深度是3千米。直径10千米的小天体可谓“顶天立地”了。它的重量可达1兆吨，撞击地球之前和大气作用的激波就可以轻而易举地把大气圈打穿一个硕大的天洞。撞上地球之后，其释放的能量，相当于全世界核裂变矿物所蕴藏能量的一万倍。人们猜测它会形成极大的火球，产生巨大的撞击坑。熔岩铺满坑底，激射出极大量的泥沙碎屑，夹杂着水、蒸汽和气化的陨石，很快形成一个直径达数十千米的热气柱，扶摇直上，到达30千米的高空，并呈现出蘑菇云状，在同温层内侧四散铺展开，而细粒喷射物更可能被带入百千米的高空。
　　白垩纪末期富含铱和撞击石英颗粒的黏土层可能就是陨石撞击地球后，在数年内的落尘堆积物。这些巨量的尘埃可能在很长时间内遮挡了阳光，使得地面植物无法接受足够的阳光，光合作用停止，因此大量死亡，造成了食物链的中断。同时这层厚厚的“毯子”反射太阳光，也可能使得全球的气候在短时间内变得干燥寒冷，很多缺乏御寒能力的生物迅速被冻死，大片森林变成荒漠。
　　但是，只要人们再进一步思考，疑问就永无止境，像这样彻底扫荡式的灭绝方式，为何只杀死了包括恐龙在内的一部分生物？从另一个角度来看，如果小行星撞击的破坏作用并没有假设的那样剧烈，那么它真的有足够的能力杀死所有的恐龙吗？一些研究指出，过去认为恐龙在白垩纪最末期突然消失的现象也许不是一个真实的现象，有些数据分析显示，在白垩纪末期，恐龙的衰落实际上经历了相当长的一个时间，也许有一百万年，甚至更长；换而言之，在小行星撞击之前，恐龙家族已经开始衰落了。情况是不是这样的呢？把所有恐龙的灭绝归咎于小行星撞击，显然还需要更多的证据。
　　还有其他“帮凶”吗？
　　现在很多人相信，恐龙的灭绝是很复杂的原因造成的，小行星可能只是其中一个因素而已。下面再介绍几种其他的假说。
　　印度次大陆等地大规模的火山喷发也被认为是导致恐龙灭绝的原因。火山喷发时会产生大量的有毒气体、炽热的熔岩流、火山碎屑流和火山灰等有害物质，并且还会造成地震、海啸等次生灾害。这些因素除了可以直接杀死恐龙之外，还可对周边的环境造成长久的污染。中国学者的研究表明，这种微量元素的污染可以影响到恐龙的生殖功能，导致恐龙蛋出现病变，孵化率显著降低，恐龙就因此“断子绝孙”。
　　还有一些假说认为：恐龙可能是因为身体不能适应新出现的被子植物而被毒死的，或是因为无法与崛起的哺乳动物竞争而遭到淘汰，或是不能适应降低的气温而被冻死。这些假说从各个侧面揭示了恐龙生活环境中可能存在的不利因素。但需要强调的是，任何一个假说和支撑它的证据都有适用的范围和局限性，都不能解释所有恐龙消亡的原因。所以像恐龙灭绝这样复杂的事件，我们也许永远无法得知它具体是怎样发生的。不过正因为如此，科学家们才有不断探索的动力。
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恐龙是怎么灭绝的？
　　虽然有体型比较小的恐龙，但是绝大多数的恐龙相对于人类来说都是些凶猛的大怪兽。要是这些大怪兽没有从这个星球上消失，人类的生活势必艰难得多。　　恐龙最早出现在2亿3千万年前的三叠纪，灭亡于约6千5百万年前的白垩纪晚期所发生的白垩纪末恐龙灭绝事件。对于恐龙的灭绝，科学界提出了许多种假想，这其中包括陨星碰撞说，气候变迁说，物种斗争说，大陆漂移说，地磁变化说等。但这些假想都存在一些不完善的地方，毕竟恐龙灭绝距今也已经过去了很长很长的时间了，人类对恐龙的研究也是从化石层面开展的，没有人真的准确知道那个时候到底发生了什么，恐龙之死如今仍是尚待解决的一个大谜团。　　正是由于恐龙的强大恐怖和它留给世界的许多未解之谜，让人类对这个已然灭绝的强大种族产生浓烈的兴趣，相信不久的将来，人们一定能一个一个揭开恐龙的谜团，还原恐龙的真相！
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- Explore the Mysteries of the extinction of dinosaurs. I was under the power of material to five-dimensional space. Is the movement of material generated by the role of scientific discovery. After exploration and research opened a mystery of the extinction of dinosaurs. Resulted in the extinction of dinosaurs on Earth because : 1. Earth's crust has been outside of the asteroid impact. So that the crust comes from the breakdown of the inner core of a huge eruption of hot magma out. Weak on the crust of an enormous force, so that the crust there have been a strong change . Is the performance of its huge earthquakes and volcanic eruptions. I think because of the growth of the dinosaur era, inclusive of the surface of the Earth's crust is thin and fragile. Frequent strong earthquakes and volcanic eruptions. 2. I was under the power of material to five-dimensional space. Is the movement of material generated by the role of scientific discovery. Through the exploration and study found that: the geological age of dinosaur life. Earth to just one out of the incubator, like soft-shell egg. Therefore At that time, the crust is very weak. There is a collision of a planet outside the breakdown occurs. For these reasons so that the core of the Earth's interior heat from the magma eruption. Resulted in the Earth's surface large-scale volcanic eruptions and earthquakes. Therefore , Resulting in the extinction of the dinosaurs. 3. For these reasons make the Earth a huge animal has been swallowed up --- dinosaurs and the extinction was eventually buried. And the fear of animals and plants was part of the hot volcanic magma buried by became the dinosaurs and fossils of animals and plants. Another part of the crust was generated by the earthquake surface cracks and wrinkles become covered in the ground to melt into the crystallization of the oil and coal. Since then, fans of the extinction of dinosaurs was I opened a. Extinction of dinosaurs on Earth, the Earth's newborn Animals and plants and start the growth and reproduction. Earth and the beginning of a new orogeny. Earth has undergone enormous changes changed in general. The following article, I confirmed that the scientific findings: Mesozoic history of the Earth has been a wide variety of live reptiles - dinosaurs. This is the key to the Earth 1.6 billion years ago a large group of animals at the end of the Cretaceous has been a sudden fall. Up to now, about all kinds of reasons for the extinction of dinosaurs could not justify the explanation, which the United States proposed by the physicist Luyiaer Varese and asteroids colliding with Earth hypothesis of much recent attention. In his study of Italian Gubbio area at the end of the Cretaceous formation of clay found trace elements - the iridium content than other rocks in a sharp increase during the 30 to 160 times, followed by people from various locations in the world have come to the same test sample Concluded that the end of the Cretaceous formation elemental content of iridium anomaly is higher universal. Alvarez then that in the late Cretaceous have a diameter of about 10 km of the asteroid impact on Earth, the dust generated by Zhetianbiri, causing the surface environment, climate change has led to the demise of the dinosaurs. However, the use of asteroids colliding with rocks to explain the increase in the content of iridium in the extinction of dinosaurs and there are a lot of doubt.1, asteroids are generally from silicon and iron elements constitute a category, such a huge asteroid falls on the earth's surface even if a long time and can not trace any, and on earth has never been found to have such a large- 2, the end of the Cretaceous strata of most of the cooling lava rock formed by the accumulation of dust from the surface only a small fraction of sedimentary rock. Only an asteroid impact dust up to the vast majority of animals and plants on Earth was buried as deep as several kilometers of rock in it? 3, an asteroid will be able to contain the element iridium evenly spread as well as covering the entire surface of the earth you Moreover, the element iridium on the existence of extraterrestrial asteroid (not a lot of content), in the depths of the Earth also exist, why Only that of the Earth from outside the Earth's interior rather than from it? In fact, the end of the Cretaceous formation of the abnormal increase in iridium content with the dinosaur extinction is indeed closely related, but through careful study has a different conclusion can be drawn. We know that in the Earth's interior to carry out the thermonuclear reaction will continue to play a huge accumulation of energy, once the earth's crust could not bear, the internal pressure to break through the crust will form a major outbreak of the release of all of a sudden. Iridium - mainly in the core element in the outbreak through the lava eruption from the depths of the Earth's crust to the surface, and recognized the signs of the end of the Cretaceous clay layer is the accumulation of a large number of volcanic dust to form (the scientists in Hawaii Kelaweiya volcanic gases emitted from the test had a small amount of iridium). Therefore, the end of the Cretaceous formation of iridium content is more precisely to demonstrate the universality of the earth's crust there have been violent eruption. File fossil tells us that the vast majority of the death of dinosaurs and the vast majority of dinosaur egg fossils in the output during the late Cretaceous period have been found in dinosaur and dinosaur egg fossils in the preservation of all the iridium-rich thin layer of clay strata , In the late Cretaceous period after the formation of the disappeared, the geological and academic circles that the end of the Cretaceous orogeny large-scale and a series of fierce global tectonic changes coincide with the time being. Originally widespread flora and fauna flourish in the face of the earth's crust after the outbreak of the expansion of the split to form the continental shelf and the mainland now, when most of the animals and plants on Earth by the eruption buried by volcanic ash and lava. Dinosaurs and other animal remains at high temperature, high pressure, isolated from the air thick rock, a long time, now turned into oil. So far as exploration in all continents (including Antarctica) and the formation of the Continental Shelf oil reserves are in the distribution of (the ocean basins are formed after the outbreak of so large an exception), the only difference between the relative concentration or just scattered. In recent years, Inner Mongolia in the Bayan called Kathmandu at the end of the Cretaceous formation, unearthed hundreds of original angle and a dragon fossil, a large number of complete dinosaur skeletons piled up together in groups, from the buried remains of the position, they are in the extreme Died in pain, of which there are a whole nest of baby dinosaur skeleton. This scenario shows that they are disastrous collective death, death and the body was buried quickly in place (in other parts of the world, many dinosaur fossils have characteristics similar to the death). At the same time found the fossil-bearing rock is a red brick powder sand rock, which by the large accumulation of volcanic ash from the fossil sedimentary rock formation is the best environment. The dramatic changes in the environment that can process all of a sudden and very short-term (new star suddenly broke out when the time-often only a few days to several months). If the Earth's environment is a gradual change in a long time, the population is the slow demise of the dinosaurs, they definitely would be heavy to very far-reaching, and will not stay buried a lot of time so the relative concentration of fossils of dinosaur eggs and dinosaur nest as a whole Fossil baby. Therefore, most of the dinosaur should be in the normal living environment has been the case all of a sudden come as a result of the devastating disaster and a large number of deaths. A large number of oil and coal, as well as possession of the earth's environment at that time reflected the characteristics of animal and plant fossils have shown that before the end of the Cretaceous, the Earth's atmosphere density and thickness than now, relatively flat surface, the world is very warm and humid climate. At that time the equator and the polar temperature difference is very small, in the 1980s, geologists in Canada's Ellesmere Island in the Arctic Circle found a shirt with water-based fossil forest, the forest there are fossils of animals such as alligators, Polar has been that with the tropical climate and environment. The natural environment is the decision of the main forms of life, after the outbreak of the Great Earth, when the bodies of those huge dinosaurs living in hot and humid environment no longer exists, even if some of the survivors could not adapt to the changes in the relative cold and dry, well-being The distinction between seasonal climate and the environment to survive. Therefore, most of the dinosaur extinction would be a natural. There are a part of the dinosaurs survived (most of the smaller body) and some as early as the Jurassic has been the evolution of ancient birds, mammals animals (such as by the evolution of the pterosaur archeopteryx), follow the natural selection, fitness The survival of the natural law, a relatively poor environment, evolving through 7000 years, most of the species has changed the original shape by the temperature of cold-blooded for the evolution of the cold temperature can adjust the blood of animals (birds, mammals And human). Of course, every time a large-scale evolution of species, there will always be some of the species to retain the status quo. As the evolution of fish to amphibians, fish still continue to survive, the reptiles are in a very small number (alligators, lizards, etc.) has maintained a 7,000 million years ago dinosaurs of the original shape. Rocks in the Earth's biological heritage revealed in the history of the evolution of life, can occur at a certain time period mass extinction of species, at the end of the Cretaceous dinosaur extinction is not the only disaster in the earlier era there have been many times. In the case of 5.4 billion years ago, most of the invertebrate in a very short period of time appear all of a sudden the "Cambrian explosion", shows that from a single biological cells to the evolution of multicellular animals, reptiles and mammals to the evolution of the same It was indeed an abrupt process (in 1984 have found China's Yunnan Chengjiang fossils as evidence). So far no clear evidence that large-scale extinction of the dinosaur extinction was caused by an asteroid impact. However, the geological structure of the earth's interior frequent changes in the (still continuing) the facts show that the cyclical changes in the tectonic (explosion) environmental "disaster" in the evolution of life has always been playing a leading role. Of course, small-scale evolution of the species is gradually throughout the evolution of life. Periodic outbreak of the celestial bodies is all the planets (including Earth) in the course of the evolution of an important and indispensable link (such as the outbreak of the Rising Star). Those in the mountains of fossils of marine and submarine oil deposits is explained as a result of the dinosaur era of dramatic change in the earth's crust and the best end of that.好了,原因和疑点都有了.
其他类似问题
for it is the time that the earth has to reborn again.
Dinosaurs ,who were too ugly to come upon loves, so they ended up going through their lives alone without having any kids and deracinated.
Why did the dinosaur extinction: environmental degradation, to dinosaur evolution, not extinction of the dinosaurs, but evolved into other creatures.
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