Fill in the blanks with your own words.
Understand the passage and type in the words based on the context
Fossils are buried in rock layers as ____A_____ of dead plant and animal materials. The totality of these artefacts and their ____B_____ on the rock formations is considered a fossil record. Fossil record is the primary source of evidence supporting the theory of evolution and the gaps in these records ____C_____ also forms the bone of contention taken up by anti-evolution theorists. Fossil records are used by scientists to understand the process of ____D_____ in general, and the subsequent changes in several species at several times of the earth's existence.