The Proterozoic Era was between 2.5 billion and 542 million years ago. One of the most important events of this era was the gathering of oxygen in the Earth’s atmosphere. Near the end of the Proterozoic Era, about 600 million years ago, creatures with more than one cell, like hydras, jellyfish, and sponges lived in the oceans. About 550 million years ago, these creatures evolved into flatworms, then round worms, and finally, into segmented worms. Thus, it was during this period that the first multi-cellular organisms came into existence. It was during the Proterozoic Era that fiery formation processes of the Hadean and the undersea continent-building of the Archaean were replaced by the process of plate tectonics. As a result, a single super-continent formed. Today, it is called Rodinia.
