Why haven’t any earth-origin meteorites ever been found?
First of all, an earth-origin meteorite would have to be huge in order to both escape the thick, burning atmosphere of Earth AND make through on the return trip. The only way an earth meteorite could be born this large is to have resulted from a catastrophic Earth impact (i.e., the Mars-size collision that may have created the Moon, or the Yucatan collision that may have killed the dinosaurs). The Earth ejecta from such an impact (called tektites) could potentially return the Earth as earth-origin meteorites. However, it would be extremely difficult to discern these earth-origin meteorites from ordinary earth rocks, given that one of our main clues for distinguishing meteorites is their unique mineral composition. If the earth meteorite was still very young, we might be able to identify it based on its melted glassy crust resulting from re-entry. For additional information on meteorites in general, please see http://www.meteorlab.
