<human>:  When did the dinosaur extinction happen?
<bot>: The extinction of the dinosaurs is generally thought to have happened 65 million years ago. The cause of this extinction is still a matter of debate, but there are several theories. One theory is that a meteorite impact caused a mass extinction event. Another theory is that the dinosaurs were hit by a series of massive volcanic eruptions. A third theory is that a series of asteroid impacts caused the extinction.