1. of, relating to, or belonging to the Proterozoic Eon, the geological time period before the Paleozoic Era, characterized by the emergence of multicellular life.
Usage: geology; also spelled Proterozoic
2. of or relating to protozoans; caused by or involving protozoans.
Usage: biology; less common usage

Examples

• Protozoic rocks contain some of the earliest evidence of life on Earth.
• The protozoic era lasted from about 2.5 billion to 541 million years ago.
• Geologists study protozoic formations to understand early planetary development.
• Protozoic organisms were mostly simple and microscopic.
• The transition from the protozoic to the Paleozoic marked a major shift in life forms.