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This is an informational tour in which students gain a basic understanding of geologic time, the evidence for events in Earth’s history, relative and absolute dating techniques, and the significance of the Geologic Time Scale.
Unlike people, you can’t really guess the age of a rock from looking at it.
The half-life of carbon 14, for example, is 5,730 years.
On the other hand, the half-life of the isotope potassium 40 as it decays to argon is 1.26 billion years.
In a way this field, called geochronology, is some of the purest detective work earth scientists do.With absolute age dating, you get a real age in actual years.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.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.Chart of a few different isotope half lifes: In reality, geologists tend to mix and match relative and absolute age dates to piece together a geologic history.