Explain why a fossil record is not 100% accurate.

Fossils form only when organism dies and suddenly buried in low oxygen environment. ... When sedimentary rocks are deep buried in the earth due to pressure above and temperature it turns into metamorphic rock and fossils destroy . Due to this rock cycle , fossil record has been lost.

The fossil record, however, is quite incomplete. Here's one major reason why: Sediment has to cover an organism's remains in order for the long fossilization process to begin. Most organisms decompose before this can happen. Fossilization odds increase if the organism happened to exist in large numbers or lived in or around sediment. For example, trilobites, ancient marine arthropods, met both criteria, so they're rather common fossils. The Tyrannosaurus rex, however, is far rarer. It was large and land-dwelling, and as a top predator made up a far smaller percentage of the population.