8: Geologic Time
- Page ID
- 36920
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Geologic time is the framework scientists use to understand Earth’s 4.6-billion-year history and the sequence of events that have shaped the planet. Geologists measure time in two main ways: relative time and absolute time. Relative time places rocks and events in a sequence without assigning specific numerical ages, relying on principles to determine which layers are older or younger. Absolute time, in contrast, provides a numerical age, often determined through radiometric dating, which measures the decay of elements in minerals to calculate when that mineral, and therefore the rock, formed. Together, relative and absolute dating allow geologists to reconstruct Earth’s history producing the geologic time scale pictured above to correlate events and interpret past environments.
