John Green explains how historians have determined the age of the Earth. He mentions that they created a quantitative chronology of human history by using ancient documents and events. He also states that various thinkers throughout history have used fossils and rocks to determine the Earth's actual age.

This clip puts into perspective how old the Earth is and how short humans have been around relative to its age.

Lucy travels through time to view the Earth at various periods in the past. As she travels, the setting behind her gradually changes in a timelapse. She visits the dinosaurs and eventually meets Lucy the Australopithecus.

Inventor Alexander Hartdegen travels 800,000 years into the future. As he travels through time, the landscape changes and develops into more complex and sophisticated terrain.

The Secret Labbers learn about gemstones from Sheila. She also gives examples of the real-world applications of minerals, such as diamonds. Watch Thomas Edison's Secret Lab on Netflix, the Kid Genius channel on Xfinity, public television and DVD. Visit EDISONSECRETLAB.COM for games, videos, downloads and more!