Geologists find the record is highly uneven. Species appear very suddenly, then show little or no change during their existence in the record, then abruptly they disappear. The majority of fossils show stability over extensive lengths of time.
Unique body plans with new features suddenly appear. More than half of all major divisions of animal life seem to have appeared in a relatively short period of time. Because many new and distinct life forms appear so suddenly in the fossil record, paleontologists refer to this period as “the Cambrian explosion.”
The “Cambrian Explosion” refers to the sudden appearance in the fossil record of complex animals with mineralized skeletal remains. It may represent the most important evolutionary event in the history of life on Earth.