The estimation of geologic time by observing rock sequences and using fossils to correlate the sequences at various locations. A current method of dating earth materials uses the known decay rates of radioactive isotopes present in rocks to measure the time since the rock was formed. The ongoing evolution of the earth system resulting from interactions among the solid earth, the oceans, the atmosphere, and organisms. The evolution of life caused dramatic changes in the composition of the earth's atmosphere, which did not originally contain oxygen. Geologic time is largely subdivided on the basis of the evolution of life and on the amount and type of crustal activity that occurred in the past.
Geologic time is ordered both relatively and absolutely.
Radiometric dating provides absolute ages for events in the earth's history. Radiometric dating techniques apply the decay rates of selected naturally radioactive isotopes to stable daughter isotopes to determine how long the unstable parent isotopes have been decaying. Students will use this page to conduct their investigation. Have them decide how to represent these events in a time-ordered sequence. Provide a roll of paper tape on which to plot the model.