About 65.5 million years ago was the start of the end of the age of the dinosaur. We know now that there was a meteor strike that happened 65.5 million years ago in Latin America and most scientists believe that or that plus a few other things is was initiated the collapse of the age of the dinosaur and initiated the rise of mammals which then leads to us. So 65.5 million years ago, there was an extinction event which scientists believe it was a meteor.
It most likely didn't kill all the dinosaurs immediately. It most likely altered the atmosphere and possibly caused a couple thousand years of a nuclear winter where the sun was blocked out if you can imagine that in your head.
The meteor was about 6 miles wide which doesn't sound like a lot to cause a mass extinction like this but it happened. So that large object striking the earth caused this havoc.
We know when this happened and where it happened.
Years ago, geologists started to notice that there was a thin layer almost like a layer of icing that existed in the same age all over the earth. Now, there is an element called iridium and it doesn't exist on earth. It only exists in outer space and so it had to be brought here and the thought is that this meteor mainly added this element and when it hit, it dispersed and it left this layer all over our planet so it's almost a fingerprint. So we know that this layer exists at 65 million years everywhere on earth and that's associated with this meteor.
The meteor hit in Latin America. The Gulf of Mexico is a meteor crater and that's where it hit and it hit about half on land and half in water.
If that didn't happen, there is a highly likelihood that dinosaurs would still be here. There is no reason why they wouldn't be and they would have evolved in any way they could have evolved in 65 million years and would still be here. However, mammals wouldn't be here.