1. Of, relating to, or denoting the geological eon that lasted from approximately 2.5 billion to 541 million years ago, characterized by the emergence of eukaryotic life and the formation of the first continents.
Usage: geology; capitalized

1. The Proterozoic eon; the period of Earth's history from approximately 2.5 billion to 541 million years ago.
Usage: geology; capitalized

Examples

• The Proterozoic eon saw the development of the first multicellular organisms.
• Rocks from the Proterozoic period are found on every continent.
• During the Proterozoic, Earth's atmosphere gradually accumulated oxygen.
• The Proterozoic eon is divided into three major eras: the Archean, Proterozoic, and Phanerozoic.
• Geologists study Proterozoic fossils to understand early life on Earth.
• The end of the Proterozoic marked the beginning of the Cambrian explosion.