Earth science relative dating activity
If certain fossils are typically found only in a particular rock unit and are found in many places worldwide, they may be useful as index or guide fossils in determining the age of undated strata.
On a larger scale, even between continents, fossil evidence can help in correlating rock layers.
If the letters "T" and "C" represent fossils in the oldest rock layer, they are the oldest fossils, or the first fossils formed in the past for this sequence of rock layers. Now, look for a card that has either a "T" or "C" written on it.
Since this card has a common letter with the first card, it must go on top of the "TC" card.
By matching partial sequences, the truly oldest layers with fossils can be worked out.
By correlating fossils from various parts of the world, scientists are able to give relative ages to particular strata. Relative dating tells scientists if a rock layer is "older" or "younger" than another.