A time scale in which the earth and its atmosphere are dated. It is broken into two division; Relative Time: Determines the age relative to other surrounding objects; Absolute Time: Obtained with radiometric dating of the object. [Holmes, A, 1937. The Age of the Earth. (New Edition Revised). Nelson: London, p.1-263.] [Harland, W.B.; Armstrong, R.L.; Cox, A.V.; Craig, L.E.; Smith, A.G.; and Smith, D.G.; 1990: A geologic Time Scale, 1989 Edition. Cambridge University Press. Cambridge, p1-50.]