The fossil records support the theory of evolution in a manner that from less complex organisms gradually over time developed more complex organisms.
The fossil records are abundant. They are found in rock layers of different ages, starting from more than half a billion years ago up until the present.
In the older rock layers of the more distant past, the fossils are of organisms that were very simple and very small. As the newer rock layers come along, the fossils are becoming bigger and gradually more and more complex. Also they provide material for comparison of the organisms and their relation. This clearly is an indicator that the living organisms started as very simple organisms and over time they developed in more and more complex organisms.