Geologic Time • Separation = Change. • Correlate geologic events, environmental changes, and changes among life forms The Geologic Time Scale • Record of Earth’s history • Names of the time periods don’t change but their boundaries are always being changed. Scale is cut into different sections: 1) Eon – longest time unit on the scale Hadean (oldest) Archean Proterozoic Phanerozoic (youngest) 2) Era – next longest span of time • Defined by the different life forms that are found in the rocks. Precambrian (oldest) Paleozoic Mesozoic Cenozoic (youngest) - Precambrian Era – microscopic life - Paleozoic Era – Age of Trilobites - Mesozoic Era – Age of Reptiles - Cenozoic Era – Age of Mammals 3) Periods – defined by the life forms that were abundant or became extinct during the time in which the rock was deposited. 4) Epochs – smaller division of geologic time.