Final answer:
The end of the Precambrian period was marked by a mass extinction, paving the way for the Cambrian explosion. Dramatic geologic and climatic changes occurred during the late Precambrian. Organisms that could not adapt died out, and new adaptations such as sexual reproduction and multicellularity emerged.
Step-by-step explanation:
The end of the Precambrian period was marked by a mass extinction, which paved the way for the Cambrian explosion. During the late Precambrian, there were dramatic geologic and climatic changes that had a major impact on Earth's life forms. Organisms that could not adapt died out and were replaced by organisms with new adaptations such as sexual reproduction, specialization of cells, and multicellularity.