The area that you can see here is in red. It covers the first four hours on the clock. This means that it covers about one billion years and it begins when earth was first formed. Think back to what was mentioned earlier about the earth being very, very hot when it first began to form. It is believed that it took around ONE BILLION years for the earth to cool down! This also gives evidence as to why, such a big planet as the sun is still burning. It takes very long for a planet to cool down.