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Superposition
Law to help determine relative age of any single section, in which oldest rocks are at the bottom (deposited first) and the youngest are at the top (deposited last)
Law of Original Horizontality
Strata are deposited in horizontal layers that are parallel with each other
Law of Original Continuity
Strata are continuous over lateral distance
Correlation
The connections between single rock sections can build up a composite section that shows all the rock strata in the region in their proper relative ages
Relative Dating
Getting events from different places in the correct order
Cenozoic
'New Life' - Acme of mammals, birds, and flowering plants. Hominids appear late in this era
Mesozoic
'Middle Life' - Age of dinosaurs. Ammonites, ichthyosaurs and pleisiosaurs in the seas
Paleozoic
'Old Life' - Age of trilobites, brachiopods, and other archaic invertebrates in the seas. First land plants, amphibians and reptiles occur late in this era
Half-life of radioisotopes
Organic fossils <60,000 can be dated directly using Carbon-14 dating (half-life of 5730 years)
Fossils >60,000 years dated by radioactive minerals; zircon in volcanic ash has U/Pb dating (half-life of 0.7-4.5 Ga)
Absolute Dating
Getting precise absolute dates for key fossil horizons and events, radioactive dating is the best
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