Geochronology

Imagine you are watching a movie with a car chase scene. The driver of one car rolls out just before his automobile plunges headlong over a cliff, and the car smashes against rocks as it tumbles down, breaking into pieces and finally exploding. You can easily tell whether the film is run forward or backward. If you ran it backward, you would see an explosion produce a broken and dented automobile, broken pieces jumping back into place, dents coming smooth as the car collides with rock on its way back up the cliff, and a man rolling into the backward speeding car.