There was this pesky little asteroid that plunged into the earth 65 million years ago. Things got smaller after that.
Hmmm, I wonder. Could that have done something to the inner earth?
There was this pesky little asteroid
I suspect it was not an asteroid that wiped out the dinosaurs. Something changed the optimum weight for land animals, from many tons, done to the much smaller size we have now. I suspect the earth suddenly started spinning much slower, and that the moon was formed, at that time, just 65 million years ago.
A far more dramatic event than a simple asteroid hitting the Yucatan with the power of a few thousand nuclear bombs causing a century long winter.