Absolute age-dating tells how long ago an event occurred. Using these methods, geologists have created a geologic time scale for organizing past times in earth’s history. For a fossil to be a good index fossil, it needs to have lived during one specific time period, be easy to identify and have been abundant and found in many places. If you find ammonites in a rock in the South Island and also in a rock in the North Island, you can say that both rocks are Mesozoic.The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah is a great example of Original Horizontality and the Law of Superposition, two important ideas used in relative dating.These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park.From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically jointed, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone.Although there might be some mineral differences due to the difference in source rock, most sedimentary rock deposited year after year look very similar to one another.
With out individual time stamps the process of dating these structures could become extremely difficult.The method of reading the order is called stratigraphy (layers of rock are called strata).Relative dating does not provide actual numerical dates for the rocks.Picture from Glen Canyon National Recreation Area, Utah.Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age, (i.e. In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another.