Why did dinosaurs go extinct?

Dinosaurs went extinct because an asteroid struck Earth near present-day Mexico about 66 million years ago and changed the whole planet. The blast filled the sky with dust and soot, blocking much of the sunlight. With plants failing, many animals lost the food they needed.

Large dinosaurs were in particular trouble because big bodies require steady meals. Smaller animals could hide, nibble scraps, sleep through hard seasons, or wait as seeds underground until better days returned. After the skies cleared, mammals spread into a world with far fewer giants.