Exactly which animals were affected ... Each eon is subdivided into eras. The Phanerozoic Eon is divided into the three eras. The oldest is the Paleozoic Era, which means ‘ancient life ...

The Proterozoic eon was the gathering up of oxygen in Earth's atmosphere, and the Phanerozoic eon coincides with the major diversification of animals, plants, and fungi.

including plants and animals, and the chemical environment in the current Phanerozoic Eon, which began approximately 540 million years ago. At the start of the Phanerozoic, carbon dioxide levels ...

You might know the Cretaceous Period for big animals such as Tyrannosaurus rex and Triceratops ... making it the longest geological period of the Phanerozoic Eon, which began some 539 million years ...