This fossil of a fish was found on the side of a 4 million year old mountain in South Dakota, sandwiched about halfway between 18 million layers of sediment.
Geologists say that each layer of sediment was laid down one year at a time.
There are persons known as Creationists who insist that the earth is only 6,000 years old, give or take a few hundred years. They say that the above fish is less then 6,000 years old.