Professor Robinson: A large meteorite impact crater in a certain region was thought to be the clue to explaining the mass extinction of plant and animal species that occurred at the end of the Mesozoic era  However, the crystalline structure of rocks recovered at the site indicates that the impact that formed this crater was not the culprit  When molten rocks crystallize, they display the polarity of Earth' s magnetic field at that time
But the recrystallized rocks recovered at the site display normal magnetic polarity, even though Earth' s magnetic field was reversed at the time of the mass extinction
No other event caused the rocks to melt after the impact formed the crater.