探索恐龍滅絕的十大理論(上)

About 66 million years ago the Cretaceous–Paleogene (K–Pg) extinction event wiped out about 80% of life on Earth, and no one is exactly sure what caused it. Many species, most famously the dinosaurs, were annihilated, while many of the survivors underwent radical transformations. Scientists have long debated the cause of one of the biggest mass extinctions in history, and while they've reached some general consensus no one is 100% certain which of the following is the cause.

大約六千六百萬年前，白堊紀第三紀（K-Pg界限）滅絕事件使地球上80%的物種都消失殆盡，但沒有人能確切地道出原因。許多物種，甚至包括赫赫有名的恐龍，都在這次事件中滅絕了，而倖存物種們則在這次毀滅性事件中經受了徹底的演化。長期以來，對於這件史上最大規模之一的滅絕事件發生的原因，科學家們一直爭論不休，然而他們已達成初步共識——沒有人敢100%的確定以下就是滅絕事件發生的原因。

roid

10.隕石撞擊說

Many of the other theoretical causes of extinction stem from an asteroid impact, and an impact event is the leading theory as to what killed the dinosaurs. Called the Alvarez hypothesis, it was developed by Nobel Prize winning physicist Luis Alvarez, his geologist son Walter Alvarez and two chemists, Frank Asaro and Helen Michels. The team discovered incredibly high levels of iridium in the sedimentary layers where the Cretaceous–Paleogene boundary is found. Iridium is uncommon in the Earth's crust, but it is common on asteroids.

關於滅絕事件的成因，科學家們提出了各種假說。很多人認爲此次滅絕事件和恐龍滅絕都源於行星撞擊地球。諾貝爾物理學獎得主路易斯·阿爾瓦雷茨，他的地理學家兒子沃爾特·阿爾瓦雷茨，及另外兩位化學家弗蘭克·阿薩羅和海倫·米歇爾斯共同提出了阿爾瓦雷茨假說（即小行星撞擊理論）。他們發現，在白堊紀與第三紀交接地層（K-T界限）中，銥的含量高於正常標準。銥元素在地殼中並不多見，但在小行星中卻很普遍。

There was only one problem — if an asteroid hit Earth, where was the crater? Well in 1990, 10 years after the theory was published, researchers found the Chicxulub crater in Mexico. It's believed that is was made by an asteroid that was about 110 miles wide and about six across — roughly the dimensions that Alvarez and his team had calculated. It's believed that after the asteroid hit it sent dust up into the atmosphere that blocked the sun for decades. This would have caused massive climate change. Adding to the darkness was ash and smoke, as wildfires would have started from debris re-entering the atmosphere. All of these factors would come together to make life impossible for dinosaurs.

那麼問題來了——如果是小行星撞擊了地球，那隕石坑在哪兒？1990年，也就是這一假說發表的10年後，研究人員在墨西哥發現了希克蘇魯伯隕石坑。阿爾瓦雷茨和他的團隊粗略的計算出這個隕石坑的容積——約有110英里長，6英里寬。科學家們認爲，行星的撞擊事件將大量灰塵升至大氣層中，遮蔽了陽光數十年，從而導致大規模的氣候變化。另外，火山灰與煙霧類的暗物質和殘骸中產生的磷火也會再次進入大氣層。所有這些因素融合在一起就導致了恐龍最終的滅絕。

al Firestorm

9.火焰風暴說

While most scientists believe that it was an asteroid that wiped out the dinosaurs, there's much debate as to what exactly the asteroid did when it hit Earth. One theory is that it started an unstoppable wall of fire that engulfed the entire planet. The argument is that when the asteroid hit, it sent vaporized rock particles above the atmosphere. There, the particles would have formed into grains of sand and then re-entered the atmosphere. The particles would have been incredibly hot, turning the sky red and making the atmospheric temperature 2700 F. This would have made the air above the point of impact act like a broiler, and everything below it would have caught fire in a blaze that would proceed to spread around the entire world. The researcher who came up with the theory said it would have been like a one-megaton bomb going off every four miles all over the Earth. Only animals that could burrow or go underwater would have been saved.

儘管很多科學家認爲行星撞擊是導致恐龍滅絕的罪魁禍首，但對於小行星撞擊地球時的具體情況也是衆說紛紜。有一種說法認爲，行星撞擊引發了難以撲滅的熊熊大火併吞噬地球上的每一寸土地。這個論點是指，當行星撞擊地球時，蒸發巖粒子會噴出大氣層，在大氣層以外的地方組成無數沙粒後再重回大氣層。這些粒子熾熱無比，將天空烤成紅色，使大氣中的溫度高達2700華氏攝氏度。受上述影響 ，空氣變得酷熱無比，像是隨時都可能爆發一場大火，蔓延至整個地球表面。提出這一假說的研究人員稱，那種場景像每四英里就有一百萬噸的炸彈在地球上同時爆炸一樣，只有穴居動物和水生生物才能得以存活。

rcanes

8.超級颶風說

Using a computer simulation, a MIT Professor theorized a super hurricane (known as a hypercane) could have theoretically occurred if an asteroid caused a 40-50 mile area of the ocean to heat to 120 F. This would have created hurricanes so powerful that Winds would have reached speeds of over 600 mph. For comparison, the most powerful storm known to human history was Typhoon Tip, which made landfall on October 12, 1979. Wind speeds reached 190 mph, less than a third of the wind speed during a hypercane.

麻省理工學院的教授曾提出一個超級颶風的理論，即通過計算機模擬，當隕石撞擊地球時，可以使40到50英里的海域溫度理論上瞬間升高到120華氏攝氏度。這個颶風威力無窮，其風速可達到600英里/小時。相比而言，目前史上最強勁的颶風是於1979年11月12日登陸的颱風泰培，其風速爲190英里/小時，卻也不及超級颶風風速的三分之一。

As long as the conditions exist to create them, hypercanes will keep forming, meaning the dinosaurs possibly contended with a number of these storms. However, the real danger is the height of the storm, which would have been 40 miles. This would have brought water into the stratosphere and deteriorated the ozone, which would have killed off any creatures that couldn't find shelter until the ozone reformed.

只要條件具備，超級颶風就會不斷形成，這也就意味着恐龍可能得一直同大量這樣的風暴作鬥爭。然而真正的危險則在於超級颶風那約莫40英里的高度，它會把地面上的水帶至大氣平流層，並惡化臭氧層，從而讓數以萬計的生物因找不到棲息地而滅絕，直到臭氧層重新形成爲止。

ual Extinction and Mammal Competition

7.物種鬥爭說

A less dramatic theory is that the dinosaurs weren't killed off with one single blow, but died off gradually over the course of millions of years thanks to competition from mammals. Mammals, which were starting to become more complex beings, could have been better at finding food and dealing with changes in the environment.

另一個比較沒那麼引人注目的理論是說，恐龍並非是一次性滅絕的，而是在數百萬年間，由於哺乳動物之間的相互競爭而逐漸滅絕。哺乳動物，就是那些正逐漸進化成高級物種的生物，他們本可以是具有更強獵食能力和應變能力的物種。

A major difference between mammals and dinosaurs is that mammals don't lay eggs. A newborn dinosaur was small but could grow to a massive size, meaning they would need a lot of food. Conversely, mammals didn't need much food and could therefore flourish much easier. And since mammals carry their children in a womb, it would have been much safer than laying an egg that would be vulnerable to predators. This theory would explain why dinosaurs died out but mammals survived the extinction event.

而恐龍和哺乳動物之間最大的區別就是，哺乳動物不下蛋。剛出生的恐龍雖然很小，但可以長得巨大，這也就意味着它需要很多的食物。相反的，哺乳動物不需要太多的食物，因而繁殖起來更加容易。哺乳動物的子宮是繁殖下一代的地方，這與易遭受掠食者的孵蛋行爲比起來，子宮育兒的方式更加安全。這個理論也許對於爲什麼恐龍在滅絕事件中滅絕，而哺乳動物卻存活下來，做了最好的解釋。

inental Drift

6.大陸漂移說

The dinosaurs are thought to have first appeared during the Mesozoic era, which was 248 to 65 million years ago. Scientists divide that era into the Triassic, Jurassic and Cretaceous periods. During the Triassic, all the continents were in one giant landmass known as Pangea. During the Jurassic, Pangea broke in half and started drifting apart. By the time the Cretaceous rolled around, which is when the K-Pg extinction occured, the two continents had broken up even more, getting closer to the continents we know today.

恐龍被認爲是在大約2480年到6500萬年前中生代出現的生物，科學家把這段時間分爲三疊紀，侏羅紀和白堊紀三個階段。在三疊紀的時代，所有的大陸是連在一起的，被稱爲泛大陸（盤古大陸）。在侏羅紀時代，泛大陸一分爲二，部分開始漂移。到了白堊紀時代，就是當白堊紀古新世時期，兩塊分開的大陸又被分成了好多塊，同目前的大陸概況很接近。

The drifting of the continents would have been devastating to the dinosaurs, as their habitats would have changed drastically. It also would have caused a change in climate, and ocean cycles would have been altered. This would have led to an increase in violent storms that would have wrecked havoc on the environment, further limiting the dinosaurs' ability to survive.

大陸漂移的過程給恐龍帶來了巨大的災難，因爲它們的生活習性也將隨之急劇改變。而且在大陸漂移中，也造成了氣候和海洋循環的變化。這會導致暴風驟雨越來越多，自然環境被嚴重破壞，進而降低了恐龍的生存能力。

翻譯:省略君 來源:前十網