Really good idea to use for any topic... after reading one book, write what they found out in one color. After reading a different book, use a different color. [No link]
Sometimes, discovering when something happened only begins to make sense when it’s seen in relation to other events. This is particularly easy to do if the total time is shown in the form of a clock. The age of the Earth is about 4.5 billion years – on the clock, 1 second equals approximately 52,000 years and one hour is 187.5 million years.