6.1.3: Life in Earth's Past

Precambrian Time: Although Earth began as inhospitable to life, simple single-celled organisms appeared over time.

Paleozoic Era: Marine invertebrates dominated the oceans during this time, with new and unique forms of life appearing.

Mesozoic Era: This was the time of the dinosaurs, as reptiles dominated nearly every habitat on Earth.

Cenozoic Era: Also known as the Age of Mammals, mammals spread throughout the world during this time and gave rise to the current dominant species, humans.