Weegy: The answer is constant and unique. User: Biologists use molecular clocks to try to measure _____.
when a molecule was created
how long molecules have existed
when two species separated from a shared ancestor
when two species will merge to become one species Weegy: 2.how long molecules have existed User: The law that states rock layers closest to the surface are the newest or youngest rock is _____.
law of original ... (More)