3. 侏羅紀恐龍滅絕（內容大部分跟TPO08的閱讀差不多）
段：長久以來，大家都很關注次物種大滅絕。但是現在中生代末期的滅絕吸引了越來越多學者的注意，原因是這次滅絕中的物種種類（考題：為什麼吸引了注意力，我選的是因為滅絕的物種很特別）。
第二段：1980年之後，隕石撞地球的說法流行起來，因為地殼中發現了銥元素。
第三段：【插入題：段首】“發現銥元素並不是的證據，而在於異常高的含量”，高含量的銥元素支援了隕石說法。同時，在河床沉積下發現的diameter－180的坑也支持了這一說法。
第四段：按照這種假設，撞擊引起地球溫度變化等等（考題：第四段的功能，我選了，描述了撞擊後可能產生的影響）。
第五段：但是這個說法不能解釋為什麼物種滅絕是selective，比如跟恐龍很類似的蜥蜴等冷血動物都活下來了。而且，大陸和海洋的滅絕應該是同時發生的，但是現在還缺少證據證明這一點。
第五段：儘管科學家現在都concede（辭彙題，選admit）這種說法，但是它是有漏洞的，還有很多其他的可能。比如，那個時候印度火山活動頻繁，可能引發氣候異常等現象（有Except題：哪個現象不是可能的因素）。
前面給了一張表，是五大集群滅絕的名稱及其發生時間。
正文開始講的是幾個滅絕事件，其中有問道為什麼白堊紀Cretaceous period，比另外一個什麼紀的受到更多關注（因為白堊紀的滅絕動物的種類多）。
之後提到集群滅絕事件發生的原因，有問到第二段和第三段之間的關係（我答：第二段提出一些因素證據，第三段是由此推出發生了什麼）。說在地球表面發現了一種元素，但是在crust裏面存在不多，認為是流星隕石所遺留的，這也是造成滅絕的主要原因。之後還說在一個地方發現了一些證據能證明是隕石造成的滅絕，好像是一個150米的大坑，還包括了三個證據，其中我記得有一個證據是什麼被沉澱物覆蓋了...還有一個是說有巨石的碎片散落...還有一個不記得了。題目有問是那哪個證據不能推出隕石造成集群滅絕。
但是有科學家懷疑隕石造成集群滅絕，因為恐龍和海洋生物的滅絕時間不同（有問為什麼專家質疑隕石造成滅絕），而且滅絕也分種類，好像是自然選擇的結果。最後專家提出可能有別的原因造成集群滅絕，也可能是這些生物已經開始進入滅絕過程，而隕石只是促進了滅絕的進行。
Controversy surrounds the extinction of the dinosaurs.
A traditional point of view held that dinosaurs were slowly driven to extinction by gradual and long-term environmental changes—changes that dinosaurs could not adapt to. Proponents of this theory postulated that dinosaurs dwindled in number and variety over several million years. Other causes once suggested for the end of the dinosaurs included epidemics or even egg-eating mammals.
Another group of theories have tied the extinction of the dinosaurs to more sudden, catastrophic events. The best known of these theories proposes that the impact of an asteroid caused catastrophic destruction of the environment, leading to the extinction of the dinosaurs. Evidence to support this theory includes the discovery of a buried impact crater (thought to be the result of a large comet striking the earth) that is 200 km (124 mi) in diameter in the Yucatán Peninsula of Mexico. A spray of debris, called an ejecta sheet, which was blown from the edge of the crater, has been found over vast regions of North America. Minerals found in asteroids and meteorites enriched material from the impact’s fiery explosion and were distributed all over the world. With radiometric dating (see Dating Methods: Radiometric Dating), scientists have used the decay rates of certain atoms to date the crater, ejecta sheet, and fireball layer. Using similar techniques to date the dramatic changes in the record of microscopic fossils, they have found that the impact and the dinosaur extinction occurred nearly simultaneously.
Although large amounts of ash suggest that vast areas of North and South America were devastated by fire from the impact, the longer-term planetwide environmental effects of the impact were ultimately more lethal to life than the fire. Dust blocked sunlight from Earth’s surface for many months. Scorched sulfur from the impact site, water vapor and chlorine from the oceans, and nitrogen from the air combined to produce a worldwide fallout of intensely acidic rain. Scientists postulate that darkness and acid rain caused plant growth to cease. As a result, both the herbivorous dinosaurs, which were dependent on plants for food, as well as the carnivorous dinosaurs, which fed on the herbivores, were exterminated. On the other hand, animals such as frogs, lizards, and small insect-eating turtles and mammals, which were dependent on organisms that fed on decaying plant material, were more likely to survive. Their survival indicates that, in most areas, the surface of Earth did not freeze.
An alternative theory links the extinction of the dinosaurs to giant volcanic eruptions in a region of India called the Deccan Traps. These massive eruptions occurred repeatedly over a period of thousands of years around 65 million years ago, releasing large quantities of carbon dioxide and other gases into the atmosphere. Some of the proposed effects of the eruptions would have been similar to those of an asteroid impact, creating a harsh environment in which dinosaurs struggled to survive.
Other scientists have suggested a combination of factors and events contributed to the demise of the dinosaurs. The asteroid impact may have been the final blow after climate change and volcanic eruptions had already reduced dinosaur numbers. Field work around the world continues to carefully document the sequence and scale of events that happened at the end of the Cretaceous period. Recent findings preserved in the sea off the coast of northern South America demonstrate that the extinctions did coincide with a single asteroid impact on Yucatán.
Extinction of the Dinosaurs (TPO-08)
Paleozoic Era 334 to 248 millions ago
Mesozoic Era 245 to 65 million years ago
- Trassic Period
- Jurassic Period
- Cretaceous Period
Cenozoic Era 65 million years ago to the present
Paleontologists have argued for a long time that the demise of the dinosaurs was caused by climatic alterations associated with slow changes in the positions of continents and seas resulting from plate tectonics. Off and on throughout the Cretaceous (the last period of the Mesozoic era, during which dinosaurs flourished), large shallow seas covered extensive areas of the continents. Data from diverse sources, including geochemical evidence preserved in seafloor sediments, indicate that the Late Cretaceous climate was milder than today’s. The days were not too hot, nor the nights too cold. The summers were not too warm, nor the winters too frigid. The shallow seas on the continents probably buffered the temperature of the nearby air, keeping it relatively constant
At the end of the Cretaceous, the geological record shows that these seaways retreated from the continents back into the major ocean basins. No one knows why. Over a period of about 100,000 years, while the seas pulled back, climates around the world became dramatically more extreme: warmer days, cooler nights; hotter summers, colder winters. Perhaps dinosaurs could not tolerate these extreme temperature changes and became extinct.
If true, though, why did cold-blooded animals such as snakes, lizards, turtles, and crocodiles survive the freezing winters and torrid summers? These animals are at the mercy of the climate to maintain a livable body temperature. It’s hard to understand why they would not be affected, whereas dinosaurs were left too crippled to cope, especially if, as some scientists believe, dinosaurs were warm-blooded. Critics also point out that the shallow seaways had retreated from and advanced on the continents numerous times during the Mesozoic, so why did the dinosaurs survive the climatic changes associated with the earlier fluctuations but not with this one? Although initially appealing, the hypothesis of a simple climatic change related to sea levels is insufficient to explain all the data.
Dissatisfaction with conventional explanations for dinosaur extinctions led to a surprising observation that, in turn, has suggested a new hypothesis. Many plants and animals disappear abruptly from the fossil record as one moves from layers of rock documenting the end of the Cretaceous up into rocks representing the beginning of the Cenozoic (the era after the Mesozoic). Between the last layer of Cretaceous rock and the first layer of Cenozoic rock, there is often a thin layer of clay. Scientists felt that they could get an idea of how long the extinctions took by determining how long it took to deposit this one centimeter of clay and they thought they could determine the time it took to deposit the clay by determining the amount of the element iridium (Ir) it contained.
Ir has not been common at Earth’s surface since the very beginning of the planet’s history. Because it usually exists in a metallic state, it was preferentially incorporated in Earth’s core as the planet cooled and consolidated. Iris found in high concentrations in some meteorites, in which the solar system’s original chemical composition is preserved. Even today, microscopic meteorites continually bombard Earth, falling on both land and sea. By measuring how many of these meteorites fall to Earth over a given period of time, scientists can estimate how long it might have taken to deposit the observed amount of lr in the boundary clay. ■ These calculations suggest that a period of about one million years would have been required. ■ However, other reliable evidence suggests that the deposition of the boundary clay could not have taken one million years. ■ So the unusually high concentration of lr seems to require a special explanation. ■
In view of these facts, scientists hypothesized that a single large asteroid, about 10 to 15 kilometers across, collided with Earth, and the resulting fallout created the boundary clay. Their calculations show that the impact kicked up a dust cloud that cut off sunlight for several months, inhibiting photosynthesis in plants; decreased surface temperatures on continents to below freezing; caused extreme episodes of acid rain; and significantly raised long-term global temperatures through the greenhouse effect. This disruption of food chain and climate would have eradicated the dinosaurs and other organisms in less than fifty years
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