It's hard to wrap your mind around the concept of 4.5 billion years. For many of us, the Pyramids–built 4,500 years ago, a millionth of that time span–symbolize the distant past. The geological time scale helps us grapple with the vast swaths of time that life has existed on Earth, dividing it into eras, periods, and epochs. With our illustrated version, explore 4.5 billion years of life in just a few minutes.