Relative dating radiometric absolute
The narrower a range of time that an animal lived, the better it is as an index of a specific time.No bones about it, fossils are important age markers.
So carbon 14 is used to date materials that aren’t that old geologically, say in the tens of thousands of years, while potassium-argon dating can be used to determine the ages of much older materials, in the millions and billions year range.For example, which is older, the bricks in a building or the building itself?Are there repairs or cracks in the sidewalk that came after the sidewalk was built?Click to expand a text description Three color coded columns.Column 1 (Nabberu) from top down: crystalline basement rocks, basinal carbonates, Granular IF with smaller bands of argillite throughout and then quartz arenite.The discovery of radioactivity and its application to dating rocks is perhaps one of the greatest scientific achievements affecting the Earth Sciences.
With the discovery of radioactive isotopes more then one hundred years ago, scientists quickly realized that the radioactive decay of materials found in rocks could be used to date the rocks and consequently change the "relative" geologic time scale into an "absolute" time scale.
Relative age dating also means paying attention to crosscutting relationships.
Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.
It’s based either on fossils which are recognized to represent a particular interval of time, or on radioactive decay of specific isotopes. Based on the Rule of Superposition, certain organisms clearly lived before others, during certain geologic times.
After all, a dinosaur wouldn’t be caught dead next to a trilobite.
In a way this field, called geochronology, is some of the purest detective work earth scientists do.