Sedimentary strata accumulate layer upon layer over millions of years. Because younger sediment always buries older sediment, the principle of superposition lets geologists read a cliff face like a book: the deepest exposed layer is always the oldest. Each colored band here represents a distinct depositional era, thicker bands meaning either a longer time span or a faster accumulation rate.
Principle of superposition: age(layer i) < age(layer i+1) for i below i+1
thickness = deposition_rate × duration
layer_age(depth d) = Σ duration_i for all layers above depth d
- Excavation depth — scrubs a virtual trench downward through time, exposing progressively older strata.
- Erosion rate — speeds up or slows the dust/erosion animation at the dig face.
- Layer highlight — colors every band by relative age instead of its natural rock-type color, making the time gradient obvious at a glance.
- Reset dig — restores the cross-section to its undisturbed surface state.
Field geologists and geoheritage sites use exactly this superposition logic to date road cuts, canyon walls, and quarry faces without any lab equipment.