Whatever is observable, measurable and repeatable is subject to the realm of scientific inquiry.  Any conclusions formed on information that does not meet these requirements is not true science.  Fossils, radiometric dating, natural time clock mechanisms and astronomy are just some of the sources used to gain insight into the age of the earth.  What do these sources have to say?  Is all the data conclusive?  How is conflicting data handled where the age of the earth is concerned?  Check the links to the left, and bring an open mind!