Debris from asteroids and comets continually bombards the Earth. Large impacts launch ejecta on trajectories that transport it thousands of kilometers from the impact site. These events are recorded in discrete layers of sub-millimeter size spherules in sea floor sediments. Larger, rarer, and interestingly shaped objects are found on land. I will describe the physical processes that occur in energetic impacts. Emphasis will be given to the mechanisms that determine the sizes and shapes of the ejecta and the cooling of the fireball. Analogies with structure formation in an expanding universe following a hot big bang will be exploited.