Geologist has been able to use evidence from the rocks, seas etc. to construct a geologic time . The geologic time gives the history and event that has modified the earth structure .
Observing rock sequence has provided important information on the relative age of existence of various sedimentary or volcanic rocks. The principle of superposition states that within a sequence of unaltered sedimentary or volcanic rocks , the oldest rocks layer are found at the bottom and as you go upward it becomes younger. Studying the sequence on how this rocks layers are laid has been able to answer question on the relative age of the various rocks and invariably used to infer geologic time.
Radiometric dating involves using radioactive elements found in rocks to determine their age. The techniques involves studying and measuring the rate at which this radioactive elements decays .Information on the age of the rocks can then be use to construct a geologic time.
Comparing fossils(preserve remains of plants and animals) found in rocks can be used to determine the relative age of rocks .Geologist correlates rocks having similar assemblage of fossil records and concludes it relative age . This relative age can then be used to construct geologic time base on the time the fossil existed within the rocks.
