What Killed the Dinosaurs?

We know for a fact that a large piece of space junk crashed into Earth 65 million years ago. We also know for a fact that the dinosaurs died out 65 million years ago. So did that impact alone kill off the dinosaurs? That, we don't know. There was also more volcanic activity around that time, and this article supposes that the additional poisonous gases added to the atmosphere might have hastened the demise of the dinosaurs.