Unit 04 · Earth's History & Geologic Time
This unit reads time out of rock: the principles of relative dating that order events without a clock, radiometric dating and half-life that put actual numbers on them, the geologic column assembled from layers worldwide, and the fossils that mark and correlate the ages. Mastery means you can read a rock sequence as a calendar millions of years deep — and grasp that geologic time is vast in a way everyday intuition is not built for.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Relative dating | Cannot order rock layers or thinks the Earth is only a few thousand years old. | Applies superposition to simple layers but stumbles on folds or intrusions. | Uses superposition, cross-cutting, and inclusions to order a disturbed sequence and defend each step. |
| Absolute dating & half-life | Treats radiometric dates as guesses or ignores half-life. | Knows half-life shrinks the parent isotope but cannot compute an age. | Uses parent-to-daughter ratios and half-life to calculate an absolute age and states its assumptions. |
| The geologic column & fossils | Sees fossils and layers as unrelated curiosities. | Names eras or index fossils but cannot use them to correlate rock. | Uses index fossils and the geologic column to correlate and date rock across distant sites. |
| Deep time | Thinks geologic time is intuitive and the Earth is young. | Recites the Earth's age but cannot place events in proportion. | Places major events on a scaled timeline and reasons correctly about durations that dwarf human experience. |
| Lab technique (half-life simulation) | Runs the simulation without tracking decay or connecting it to time. | Collects decay data but misreads the half-life from it. | Runs a half-life simulation, reads the decay curve, and converts a parent-daughter ratio into an age. |
| Integration (cross-domain) | Treats the science as isolated facts; makes no cross-domain connection. | Names a link to history, reading, or writing but cannot defend why it matters. | Connects the unit to its anchor across History · Reading · Writing (plus chosen electives) and defends why the connection matters. |
“The intrusion cuts across the layers, so it’s younger than all of them — that’s cross-cutting. To get a real number I used the parent-daughter ratio: two half-lives had passed, so the rock is about that old. Steno, Hutton, and Lyell built the case for deep time layer by layer.”
“The Earth’s only a few thousand years old, right? Radiometric dates are basically guesses. A million years, a billion — same idea.”
You demonstrate this unit through a half-life simulation and relative-dating sequencing plus short oral checks where you reason from the evidence aloud — not a multiple-choice test. A criterion counts as mastered only when you can both order the events and justify the ages behind them. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.