A matter-of-time scale.

If the age of the earth (4.6 billion years) were condensed into one year ...

Jan. 1 -- Earth was born
Early Feb. -- Oldest known rocks formed
Late Mar. -- First primitive life formed
Mid Nov.-- First complex life with shells or skeletons formed
Late Nov. -- First land animals
Dec. 25 -- Extinction of the dinosaurs
Dec. 31 -- Humans evolved in the evening
Dec. 31 -- one second before midnight, humans first set foot on the Moon