Relative dating using fossils


Geologists establish the age of rocks in two ways: numerical dating and relative dating. Numerical dating determines the actual ages of rocks through the study of radioactive decay. Relative dating cannot establish absolute age, but it can establish whether one rock is older or younger than another. Relative dating requires an extensive knowledge of stratigraphic succession , a fancy term for the way rock strata are built up and changed by geologic processes. In this lesson, we'll learn a few basic principles of stratigraphic succession and see whether we can find relative dates for those strange strata we found in the Grand Canyon.

William Smith's collecting and cataloging fossil shells from rocks led to the discovery that certain layers contained fossils unlike those in other layers ( see: fossil sorting ). Using these key or index fossils as markers, geologists began to identify a particular layer of rock wherever it was exposed. Because fossils are believed to record the slow but progressive development of life, geologist use them to identify the relative age of rocks throughout the world. [2]


Relative dating using fossils

Relative dating using fossils



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