Fossil Hunt
Use index fossils to match rock layers and determine their relative ages.
Scientists use index fossils to estimate the age of rock layers and reconstruct Earth's history.
Fossils are the remains or traces of organisms from the past. Some fossils are especially useful for helping scientists determine the age of rock layers, these are called index fossils.
Useful index fossils have evidence for these features:
Fossils help scientists date rock layers without using a clock. They help compare layers found in completely different parts of the world. And together, they let geologists reconstruct billions of years of Earth history, one layer at a time.
Investigate a layer, then search for a matching fossil in a different location to link them.
Includes highlighted reference evidence and fewer horizons.
Use fossils and their age ranges to match rock layers from different locations. Remember: in undisturbed rock layers, older layers are below younger layers.
These rock layers are simplified examples. Use the fossil names and information provided as evidence. You do not need to memorize fossil names or dates. mya = million years ago.
Fossil Hunt — Educator Guidance
Required Grade 6 activity; ESS1-4 remains classification C. These fictional columns model selected layers in undisturbed sequences, with omitted time and no reworked fossils. They are not an actual measured outcrop or a record of continuous deposition. Rock color, name, thickness and screen height between sites are not dating evidence.
Identification is supplied. Glyphs are schematic, not diagnostic illustrations. Students reason from the cards, without memorizing Latin names, taxonomic ranks, periods or dates. Named markers have more restricted reference intervals than their broad groups. Rounded brackets enclose geological intervals; they are not exact taxon lifespans, first appearances, extinctions or layer dates. Distribution is scoped to the cited reference setting; these different markers do not establish one real region shared by the entire fictional sequence.
Practice: G1 ammonite Dactylioceras commune; G2 crinoid Scyphocrinites; G3 trilobite Paradoxides. Oldest to youngest: G3 → G2 → G1. Challenge: G1 Dactylioceras commune; G2 brachiopod Mucrospirifer mucronatus; G3 Scyphocrinites; G4 Paradoxides. Oldest to youngest: G4 → G3 → G2 → G1. Broad Rugose Coral is contextual evidence (about 470–252 mya), not a narrow marker.
Correlations support corresponding intervals, not exact simultaneity. Lower layers are older within each undisturbed sequence. Require agreement between marker intervals and this relative order. The youngest correlated marker is not the youngest layer: Challenge A0 lies above A2, but its unidentified shell cannot establish precise correlation of top layers.
Practice highlights reference evidence. Challenge removes those highlights and undiscovered answer labels, but retains supplied identifications, hints and feedback. Ask students to explain the evidence and its limits orally; scaffolded completion and selected responses alone do not establish independent reasoning or an authored SP6 explanation. This activity contributes to ESS1-4; it does not assess every requirement, including cross-cutting relationships and long-term geological processes.
The existing submission retains score, response letters and summary counts. It does not retain students’ match arrangements, order attempts, final-check reasoning or written explanations. Richer retention is deferred to Student Evidence Architecture.
Reference basis: BGS Jurassic zonation; Scyphocrinites study; BGS trilobites; regional Mucrospirifer study; rugose coral context; geological interval boundaries; geological principles; Massachusetts STE framework.
More Learning
You used index fossils to correlate layers across sites and read the rock record like a timeline. Take that skill back to the framework it belongs to.