The fossil record is considered incomplete for several reasons. One major factor is the conditions required for fossilization. Not all organisms are equally likely to be preserved after their death; typically, hard-bodied organisms like mollusks and bones of vertebrates are more likely to fossilize compared to soft-bodied creatures like jellyfish or most worms. Environmental conditions play a key role as well; sediment may not settle over all organisms, and some may decay before becoming fossilized.
Moreover, many organisms lived in environments that are less conducive to fossilization, such as forests or deep ocean floors, where conditions aren’t as favorable for preserving remains. Additionally, geological activity, erosion, and other natural processes can destroy existing fossils or prevent them from being discovered.
Because of these factors, there is a significant underrepresentation of soft-bodied organisms in the fossil record. For instance, early life forms such as sponges or early multicellular organisms often do not leave behind fossilized remains. As a result, the fossil record tends to favor certain species and ecological scenarios, leaving many gaps that make it challenging for scientists to piece together a complete picture of Earth’s biological history.