Text Box: Pre Cambrian Era                 Formation of Earth & atmosphere; beginning of life Paleozoic Era                       Life explodes first in the oceans and then on land; nearly wiped out Mesozoic Era                      The age of dinosaurs Cenozoic Era                       The current era         Text Box: Proterozoic Eon 2,000 - 545 million years ago Origin of photosynthetic eubacteria • Oxygen accumulates in atmosphere • Origin of aerobic respiration Text Box: 545 million years ago just prior to the "Cambrian Explosion" of complex life Text Box: 4.6 billion years ago creation of Planet Earth Text Box: Pre-Cambrian Era 4.06 billion years long = 88% of the Earth's history