From your knowledge of biological evolution, what characteristic of organisms older than 540 million years ago makes fossils of these life forms relatively rare?

Any worms or soft bodied animals are rare to find because they decompose and don't leave anything to fossilize such as bones

The fossils that are more than 540 million years old are hard to get on earth due to their low preservation potentials because of the following conditions-

1) Lack of hard parts in the organisms does not lead to the formation of fossils. These organisms were soft-bodied.

2) Due to the occurrence of different mass extinction in geological time, the fossils might have destroyed.

3) Due to the constant plate tectonic activities that take place on earth, these fossils were damaged.

4) The fossils existing in a particular area also gets affected if there occurs intrusion of magma, that burns the fossils. The more ancient fossils are difficult to obtain because of the various geological processes that undergo on earth. So, the fossils of recent ages are mostly found on the beds of sedimentary rocks.

5) Some fossils are also not found because they are buried deep under the earth's surface.