However,some believe that major collision in the past show a pattern which the next one may come soon. Monica Grady,an expert in meterorites at the Open University,say:It's a question of when,not if, anear Eart object collide with Earth.Many of the smaller objects break up when they reach the Earth'satmosphere abd have no impact.howere, an NEO largar than 1km. (In width) will collide with earth every few hundred thousang years and an NEO larger than 6 Km, which could cause mass extinction,will collide with Earth every hundred milion years.Many scientists believe that if such events follow a regular pattern,we can expect another one at any time. We are overdue for a big one Grady says.