Impact craters on Earth, Moon and other planets provide evidence that the Earth has been struck by asteroids since it formed roughly 4.5 billion years ago. Once every few million years, an object large enough to threaten life on Earth comes along. Meteorite specialist Denton Ebel, Curator in the Division of Physical Sciences, provides a brief history of impacts from the early days of the solar system to the impact that might have led to the demise of most dinosaurs on the planet.