Earth didn't always have oxygen, so what caused the change that allows humans to live here? Learn about the change in O2 levels throughout geological history through an interactive graph. Each section offers greater detail on the changes...

Everything evolved from a common ancestor, but how did modern plants and animals develop so many more genes? Scholars use an online interactive to learn about the process. They begin to understand common genes with an animation, multiple...

Explore the evidence for human evolution in this interactive timeline - climate change, species, and milestones in becoming human. During the period of human evolution, the Earth's climate has fluctuated between warm and cold. Some of...