The story behind the timelines: This color band, and the similar band at the top of this page, are timelines showing the history of the universe (top) and the history of our planet (bottom). The length of the top band (960 pixels long) represents a time span of 13.7 billion years, currently our best estimate for the age of the universe. That band is divided into two color seegments; the length of the darker one on the right represents the proportion of the history of the universe since formation of Earth, roughly 4.6 billion years ago. The lower color band represents that time period, with color bands proportional to the geologic eras of Earth history; from left to right, these are the Archean, Proterozoic, Paleozoic, Mesozoic, and Cenozoic eras. Our hominid ancestors are likely to have first appeared on Earth between 5 and 6 million years ago, a distance of roughly 1/1000th of the length of the bottom band...just about one pixel.