As an example, consider Carbon: All atoms of Carbon consist of 6 protons and 6 electrons.
Obtaining such a solution is beyond the scope and requirements of this class, though with 1-2 years of calculus, you to could do the impossible.
The original source for the sediment may have been diverse, consisting of different rock types of different ages.
Consequently, a sedimentary rock such as a sandstone or a shale is likely to consist of framgents of different age.
The Geologic Time Scale (courtesy of the Geological Society of America) UC (Berkeley) Museum of Paleontology Exhibit on Geologic Time For an informative description of the historical development of the Geologic Time Scale and the principles of geology that have been used to develop it, please visit the Berkeley Museum of Paleontology web page cited above.
I also encourage you to visit the links within the Berkeley page to learn more about the divisions (Eras, Periods, etc.) of the time scale, their stratigraphy, life forms and other useful bits of information. Students will learn about the principles of Stratigraphy and application of various techniques.