Though today the biggest theory on the extinction of the dinosaurs is that a meteor destroyed all of the dinosaurs. But it is always important to look into alternate theories no matter how ridiculed for many of the biggest breakthroughs in science and history were ridiculed.
Before I go into alternate theories I think I should talk about the major theory. The asteroid theory is simply that a massive meteor roughly 9 miles in diameter struck the earth. Were most meteors burn up in the atmosphere if even a small asteroid strikes then the devastation can be incredible so if meteor lands that is nearly 10 miles across then not only would it destroy everything around it but it would also affect the weather and climate. Scientists believe that the meteorite struck in the gulf of Mexico. It should be noted that the geography of the world was a different back then.
Then the second most accepted theory that global warming killed the dinosaurs. Wait what? Well you probably already know the basics of global warming (I'm assuming) and aren't things like cars nuclear power plants and factories supposed to release the green house gasses? Well yes that's true (I am subliminally telling you to recycle) but volcanoes also give out green house gasses as well as other chemicals that damage the environment and the biosphere. I personally believe that both this theory and the meteor are true. Because volcanoes can be activated by powerful earthquakes and the meteorite would release powerful tremors nearly throughout the entire planet which would then activate volcanic eruptions. It should also be noted that there were far more active volcanoes back then, than there is now.
Then there is another theory that the dinosaurs killed themselves, well sort of. I don't mean by fighting each other by killing themselves I mean their evolution brought them to a dead-end. As time went on studies of shown that older eggs had far thicker shells but the more recent eggs had thinner shells. This would's put the baby dinosaurs at a greater risk. Also another part of this theory is that they were out evolved by mammals. The reason for this is because they had really small brains. You have probably have heard of statistics of laterally being pea brained having a brain the size of a pea. But you need to remember that many of these dinosaurs were huge and having a brain a little bit bigger then a walnut control so much mass would make you pretty dumb.
Now this one is my favorite and though it seems ridiculous I implore you to give it some thought. Caterpillars killed the dinosaurs scientists have found that caterpillars went through several evolutionary changed during the time that dinosaurs died off. It is believed that the caterpillar in your back yard had ancestors that were able to reproduce at a rate that allowed them to eat huge amounts of vegetation which would in turn kill the dinosaurs as the herbivores would die followed by the carnivores.
Then another theory is that they died off of disease. During this time is believed that several land bridges had appeared which would allow dinosaurs to migrate. If you know the story of the Indians then you probably can guess where this ends. As the dinosaurs lost there long distant cousins they would exchange diseases that the other one would not be able to handle as their immune system would be unable to cope.
Now the last of the theories is the theory that a supernova destroyed the dinosaurs. It should be noted that there very little evidence that this theory is true if any at all. However many scientists argue that it is a very real possibility. The theory states that a distant star went supernova even though we were far away from the explosion itself we were still affected by the radiation. Which would destroy nearly everything on the surface of the planet.
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