The first question that must be posed when trying to crack the mystery of themass extinction is to ask, throughout history were there any other occurences ofthis magnitude? The answer is a resounding yes.
Altogether over time there hasbeen about eight mass extinctions to large land dwelling vertebrates. The mostrecent was about ten thousand years ago, killing most of the giant mammals likemammoths, mastodons, super-large camels, saber-toothed tigers, and others (Bakker428). The second question, is whether or not these mass extinctions follow apattern? Once again the answer is yes. Every time a mass extinction occurs onthe land ecosystem, the oceanic system is hurt. When the dinosaurs died, manysea animals also died out (Bakker 428-430). The final question to be asked, iswhen these mass extinctions occur, are both land and water animals affected, andif so, are they affected at the same point in time? All saltwater animalssuffered, however, freshwater creatures were left unaffected.
Plants on land didsuffer, but not nearly as much as the dinosaurs and other creatures thatdepended on them as a food source. (Bakker 431). Since the time that the firstdinosaur was discovered, paleontologists have been pondering the demise of thedinosaurs. Over a hundred theories have been produced to explain this massextinction (Psihoyos 255). The dinosaurs may have died because, “theweather got too hot,” ; “the weather got too cold,” ; “theweather got too dry,” ; “the weather got too wet,” ; “theweather became too hot in the summer and too cold in the winter,” ;”the land became too hilly,” ; “new kinds of plants evolved whichpoisoned all the dinosaurs,” ; “new kinds of insects evolved whichspread deadly diseases,” ; “new kinds of mammals evolved whichcompeted for food,” ; “new kinds of animals evolved which ate all ofthe dinosaurs’ eggs,” ; “a giant meteor hit the earth,” ; “asupernova exploded near the earth,” ; “cosmic rays bombarded theearth,” ; or “massive volcanoes erupted all over the earth at once (Bakker425). ” Scientists’ beliefs seem to fall into two basic common positions,the Catastrophists, and the Gradualists (Psihoyos 255).
The Catastrophistsbelieve that a huge catastrophic event took place, killing all of the dinosaurs. The most popular theory of the Catastrophists is the asteroid theory. Anasteroid called Chicxulub hit the earth creating a 150 mile wide crater near theYucatan Peninsula in Mexico. The date this asteroid hit the earth was sometimeabout 65.
7 million years ago, just about the time the dinosaurs died (Psihoyos255). When this two-mile-wide asteroid hit the earth, it probably shattered andsent tons and tons of asteroid-earth dust into the stratosphere. The lack oflight caused by the dust blocking out the sun would have caused many plants todie out, leaving plant eating dinosaurs to die, and with no herbivores to hunt,the carnivorous dinosaurs would die out, the domino effect (Krishtalka 19-20). This event also would have frozen the earth, another reason why it would killall of the dinosaurs. No one can prove this theory, but it is one of the mostrecent theories among scientists these days, as to what killed off all of thedinosaurs. The dinosaurs were around for roughly 140 million years.
They werethe ruling beasts of the earth for this whole period. Then, 65 million years agothe dinosaurs just all died. None flying through the air, none swimming in thewater, none walking on land. They were all just gone. “The death of thedinosaurs was the biggest mass extinction in the history of the earth (Bates8-10). ” The first clue that led scientists to the asteroid theory was thefinding of a thin layer of clay in the ground.
In 1978 Walter Alvarez, aProfessor of geology from Berkeley, California, was driving up out of a deeplimestone gorge behind Gubbio, Italy, when he noticed something strange. Limestone was formed when little prehistoric sea animals called forams died andfell to the bottom of the ocean to form rock. When he was driving along he sideof this gorge he noticed that right at one point, all of the forams were gone. This also happened to be a point in the ground right at 65 million years, rightabout the time the dinosaurs died. Another strange thing Alvarez noticed wasthat right in between the forams and the above rock was a thin layer of clay. Hefelt that the clay might be important so he chipped a piece off, and hid itaway.
Upon his arrival back in California he showed the clay to his father, LuisAlvarez. Together they decided to find out what this clay was doing in themiddle of the rock. To see how long the clay took to form, the measured thedensity of iridium, a metal in cosmic dust that the earth collects as itrevolves around the sun. To their amazement, though, the clay contained massiveamounts of iridium.
Now they didn’t care how long the clay took to form, but whyit contained so much iridium. After a while, they came up with a working theory. Perhaps a comet or asteroid crashed into the earth. Both of these containextremely high amounts of iridium, so it was a perfectly working explanation. Upon impact this heavenly body would smash into millions of little pieces, flyinto the atmosphere, and cause destruction on the earth (Bates 11-14).
This clayis a marker between the Cretaceous and the Tertiary periods. It is now calledthe K-T boundary. When the K-T boundary was looked for in New Zealand and inDenmark, it was still found. There is another place the iridium could have comefrom, and that is the center of the earth. But, unless volcanoes erupted allover the entire world at once, this is a very unlikely place for it to have comefrom.
So, with all this in mind, the answer became very clear for Luis andWalter Alvarez and their colleagues. This clay layer came from outer space (Krishtalka20-21). Finally, in the early 1990’s, researchers found something very exciting. They had discovered Chicxulub. Chicxulub is a non-volcanic crater buried in theGulf of Mexico.
This crater is more than a hundred miles across. The size,structure, and composition of this crater led scientists to believe thatapproximately 65 million years ago an asteroid, two miles in diameter, cameflying towards the earth (Horner 208). As scientists look at the K-T boundary,they noticed something else strange, nowhere on earth can dinosaur remains befound on or above this line of clay. In fact, the closest any remains have beenfound were about nine feet below it.
It would be hard for scientists to sayexactly how many years nine feet of earth represents, but it’s safe to say itwould be around 100,000 years. Experts who feel an asteroid killed the dinosaurssay that it just took all of 100,000 years for the dust cloud to resettle to theground, and by that time, the dinosaurs were long gone (Horner 211-212). Anothercause, less common, yet still possible, for the extinction of the dinosaurs, isthe “Deccan Trap” thoery. The Deccan Traps was a massive volcanic eruptionthat took place just about the time the dinosaurs died. So much lava was spewedin this eruption that the Himalayan Mountains were formed. Also, though, enoughash could have been thrown up into the atmosphere in this eruption, that the sunwould have been blocked out, killing the dinosaurs, some plants and otheranimals (Psihoyos 255).
Researchers are beginning to agree that a catastrophicevent at the end of the Cretaceous caused mass mortality, but not immediateextinction. This is ironic, however, because for years scientists have tried toprove this catastrophe caused sudden and rapid extinction. Now that rapidextinction has been accepted, it turns out it wasn’t so rapid after all (Hs?221). This is exactly what the gradualists believe, that this extinction wasslow. They believe this extinction was brought on by something like climatechanges, smaller volcanic eruptions, rampant spreading of deserts, or thedrainage of inland seas.
All of these, however are caused by continental drift. This is a weak belief, though, because as paleontologist Jim Jensen said,”Continental drift can be used to explain everything- from lousy weather toRepublicans (Psihoyos 255). ” If the dinosaurs died slowly, it would be verylikely that the cause would be more random than a single catastrophic event. Some members of some groups may be eliminated, but not all members of any onegroup. Looking at certain studies, this is what scientists found, a steadydecline in genera of dinosaurs from the oldest (deepest) layers of the column,to the youngest (Horner 213-214).
A column of sediments in North Dakota, “Adetailed breakdown shows that the apparently fixed number of species owes muchto rapid recovery after mass extinctions. . . Species diversity was drasticallyreduced at the end of each geological era, not only at the species level, butamong genera and families too (Hs? 94). ” There are also a fair number ofscientists who believe in both kinds of theories. They have called thecombination of events that led up to this extinction, “The worst weekend inthe history of the world (Hs? 95).”
