Read Life’s History Across Geological Time
Place events in geological order, then distinguish relative dating from radiometric dating.
Geological History and Fossil Dating is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Read strata and the time scale
In undisturbed sedimentary sequences, lower layers are generally older. Silurian precedes Permian, which precedes Triassic, followed by Cretaceous. Dinosaurs became dominant in the Jurassic; the Triassic was earlier. Geological events and groups can be ordered by these broad intervals.
Apply radioactive decay
Carbon-14 decays after an organism dies.
With a half-life near 5,700 years, a sample retaining about 71% of its original C-14 is roughly 2,800 years old.
Recognise transitions and lineages
Latimeria is a lobe-finned fish discussed in the fish-to-amphibian transition. Evolutionary timelines also track early plants and reptile lineages; avoid transferring a feature of one dinosaur group to another.
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- ✓Lower strata are usually older.
- ✓Silurian → Permian → Triassic → Cretaceous.
- ✓Jurassic—not Triassic—is the keyed period of dinosaur dominance.
- ✓Carbon age uses the fraction remaining and the half-life.
Do not confuse relative layer order with a numerical date, or mix up geological periods.
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