1. http://en.wikipedia.org/wiki/Big-bang .
2. http://www.dailygalaxy.com/my-weblog/2007/12/earths-clock-of.html .
3. http://paleobiology.si.edu/geotime/main/htmlversion/archean3.html .
4. http://www.answersingenesis.org/articles/cm/v3/n3/primitive-atmosphere .
5. http://en.wikipedia.org/wiki/Human .