Geologic Time Scale Overview

Geologic Time Scale Overview

The geologic time scale is a system used by geologists and paleontologists to describe the timing and relationships between events in Earth’s history.

Main divisions (large to small):

• Eons → Eras → Periods → Epochs → Ages

Relevant parts for dinosaurs:

• Phanerozoic Eon (last ~541 million years)
  • Paleozoic Era – ancient life (before dinosaurs)
  • Mesozoic Era – Age of Dinosaurs (₂₅₂–66 Ma)
    • Triassic Period
    • Jurassic Period
    • Cretaceous Period
  • Cenozoic Era – Age of Mammals (66 Ma–present)

Why this matters for dinosaurs:

• Dinosaurs appear in the Late Triassic.
• They dominate land ecosystems in the Jurassic and Cretaceous.
• Non‑avian dinosaurs disappear at the end of the Cretaceous.

Use the child thoughts for each period (Triassic, Jurassic, Cretaceous) for more detail about which dinosaurs lived when.