Which sequence lists geologic time periods in the standard order from oldest to youngest?

Which sequence lists geologic time periods in the standard order from oldest to youngest?

• A. Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous
• B. Cretaceous, Jurassic, Triassic, Permian, Carboniferous, Devonian, Silurian, Ordovician, Cambrian
• C. Cambrian, Silurian, Devonian, Permian, Triassic, Jurassic, Cretaceous, Ordovician, Carboniferous
• D. Permian, Carboniferous, Devonian, Silurian, Ordovician, Cambrian, Triassic, Jurassic, Cretaceous

Answer: (A)

Geologic time is arranged from oldest to youngest by the ages of rocks and their fossils. The standard order of these periods from oldest to youngest is Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous. This sequence lines up with the fossil record and major changes in Earth’s life and environments across deep time. Starting with a younger period or swapping the relative ages of periods (for example, placing Cretaceous first or moving Ordovician after Jurassic) would contradict what the rock layers and fossils tell us about the timeline.

Geologic time is arranged from oldest to youngest by the ages of rocks and their fossils. The standard order of these periods from oldest to youngest is Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous. This sequence lines up with the fossil record and major changes in Earth’s life and environments across deep time. Starting with a younger period or swapping the relative ages of periods (for example, placing Cretaceous first or moving Ordovician after Jurassic) would contradict what the rock layers and fossils tell us about the timeline.