Dinosaurs were already struggling before the asteroid strike that doomed them to extinction, study finds By Katie Hunt, CNN enablePagination: false endIndex: (CNN) — It was an asteroid strike that doomed the dinosaurs to extinction 66 million years ago. But what were their lives like before it hit? Whether they were thriving or already teetering on the brink has long been a matter of debate for paleontologists. A new study suggests that dinosaurs were in decline for as many as 10 million years before the city-sized asteroid that hit off the coast of what is now Mexico dealt the final death blow and that this decline impeded their ability to recover from the asteroid's aftermath.