The geologic time scale originally ordered earth's rocks by

The geologic time scale originally ordered Earth's rocks by relative age.

Explanation:

Geologic time scale is the measure of events occurred in year wise from the starting of universe. Mostly dating of rocks and fossil fuels are doing the trends still now. In order to measure the age of rocks, geological time scale have preferred relative age mode.

In this system, the age of rocks are measured and compared layer by layer. So the lowest layer of rock will be having the maximum age. As we don't know the starting time of universe, so this method of comparison between the layers to order the rocks is best. So, depending upon the position of the rocks, the age can be determined.