Relative dating is the same as radioactive dating

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To determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones. This rule is common sense, but it serves as a powerful reference point.

Geologists draw on it and other basic principles ( to determine the relative ages of rocks or features such as faults.

Our understanding of the shape and pattern of the history of life depends on the accuracy of fossils and dating methods.

Some critics, particularly religious fundamentalists, argue that neither fossils nor dating can be trusted, and that their interpretations are better.

Radioactive elements are unstable; they breakdown spontaneously into more stable atoms over time, a process known as radioactive decay.

His geological cross-section may look something like Figure 2.A commonly used radiometric dating technique relies on the breakdown of potassium (Ar in an igneous rock can tell us the amount of time that has passed since the rock crystallized.If an igneous or other rock is metamorphosed, its radiometric clock is reset, and potassium-argon measurements can be used to tell the number of years that has passed since metamorphism.Early geologists, in the 1700s and 1800s, noticed how fossils seemed to occur in sequences: certain assemblages of fossils were always found below other assemblages. Since 1859, paleontologists, or fossil experts, have searched the world for fossils.In the past 150 years they have not found any fossils that Darwin would not have expected.

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