How do fossils provide evidence to support the theory of the evolution of earth?

Fossils provide direct evidence of evolution. They show the changes of animals from ancient organisms to present form. Fossils are the preserved remains of earth layers. There are 4 types of fossils-

Original fossils that are not very old.  e.g. teeth, skeleton, shells.

Frozen fossils

less permanent fossils

casts, molds,  and prints - wings, skin, leaves, etc.

The fossils show the adaptive radiation in horses, humans. The transition fossils form the connecting link between different groups such as fish and amphibians, reptiles and birds, etc.  

e.g. Archeopteryx is the connecting link between the reptiles and birds.

The modern horse Equus have several ancestor species, we came to know from the fossil records.

The fossil record shows the evolution of humans and their ancestors.

the answer to your question is tooth decay.

the answer is true ; ) have a good day