Geologic History
Imagine Earth during its primordial formation: it’s a magma ocean like the picture you see here, with toxic gases in the atmosphere instead of the life-sustaining oxygen-rich atmosphere of today. No life is found on Earth, and no life will be found for nearly one billion years. As you will learn in this unit, life slowly emerged on our planet. It then began to diversify and evolve from simple bacteria, to the swampy forests of dinosaurs, to the rise of human civilization.
This unit is the story of a changing Earth. It tells the story of how Earth and its life forms have changed through time–4.65 billion years of time. Throughout this unit, you will learn about how scientists study geologic time–time that goes back millions and even billions of years. You will see how geologic time is divided and studied and how Earth has changed through all of those long years.