Why dinasour extinct

You must wonder why I suddenly come up with this. Actually, my lecturer told me this. Althought we must have heard they extinct because comet dropped on earth. Yes. That's the main cause. But wat happen after the comet crash is what should be paid attention. Scientists discovered large crate (holes left by comet) in the sea, this proves that the comet really dropped on earth. In many writings, they says earth has been through Ice Age. It's true. Now, let me explain. Comet crashed on earth at high speed and extream heat, reaching 5000˚c, which is far hotter than earth's highest melting point object, diamond, which is merely 3500˚c. So, basically all object melted when the comet crashed. The vaporation of the melted object in form of dusts and carbons covered the whole atmosphere, thus sunlight could not warm the earth. And then, the Ice Age begins. So, as the explanation goes, do you think dinasours are able to survive in 5000˚c? If they happen to be at the other side of the world, could they survive at a temperature way below 0˚c? What do they at to survive when plants even died? So, they extinct. Then, another age begins. Wow, looks like something in "The Day After Tomorrow". ^.^