The evidence is all around us; worldwide flood killed the dinosaurs.
Somehow the asteroid theory of dinosaur extinction still breathes and has life. I'm here to tell you it shouldn't. It's a grasping at straws.
Despite the worldwide availability of evidence that shows all the various animals being killed and buried in a big flood, scientists and science fiction writers have found that an asteroid is the only thing big enough to have caused a whole group of a animals to go extinct. After all, a volcano is not big enough to mess the world's ecology up enough to kill everything. And not all dinosaurs are fossilized in volcano ash.
There is another more plausible reason for why the dinosaurs went away. The earth cracked apart at the seams, like a baseball that ripped its stitches. The great fountains of the deep exploded into the atmosphere gushing super-heated water and a brine of chemicals that mixed with the elements of the earth and literally buried everything under water.
The settling of the earth caused the waters to regather forming the oceans of today, and all that run-off water eroded and dug the Grand Canyon while everything was still pretty mushy and muddy. Who knows how long it took for this mucky mess to set up.
When you poor concrete it's not rock-hard for sometimes years, while the mix cures and fully sets.
That might explain why so many things used to be made of cut stone. Stone was not as hard as it is today.
Anyway, the gist of all this kids is to put your mind at ease. The dinosaurs where mostly killed in Noah's flood.
The atmosphere and oxygenation of the air probably changed a lot, and as a result the reptiles of the world just aren't able to grow as big as they used to. Many reptiles are that way, they grow their whole life, and would reach larger sizes is they were able to get enough oxygen to support their growth.
So take your asteroid theory and put it where the sun don't shine on the dark side of the moon.