Earth History and Fossils

Many organisms do not have structures that can be fossilized. (There bodies are made of soft tissues instead of shells or bones)

Some environments do not provide conditions favorable to fossil formation. (If the environment is not made from sedimentary rock we will not have fossils.)

There are lots of fossils that we haven't found yet. (Because you need to either dig or look in mountains we are still searching for many fossils/ index fossils to help us fill the gaps of the fossil record.)

Some geological events destroyed fossils that were in the rock layers. (Things like earthquakes and volcanic eruptions may have destroyed important fossils).

All of the above.

millions

billions