Uncover the ammonite before the tide returns. Brush the loose sand, chip the hard rock with care, then measure the spiral. Virtual dig: real fossil sites have rules, tides and crumbling cliffs, so check tide tables and local advice first.
Press Inspect to look from above. Slide W until the gold spiral lies along the dark sutures between whorls. W is how much each whorl grows per full turn: W = r(θ+2π) / r(θ). Needs at least 70% revealed.
Curve: sea height above chart datum over one tidal cycle. Dashed: slab level minus a 0.3 m safety margin. The vertical mark is now.
The science
What you see. A ribbed ammonite (a stylised shell, not a named species) in a limestone slab on a tidal rock platform. Vertical relief is exaggerated ×2.5. The coast, cliffs and shells are inspired by the Jurassic Coast; the scene is artistic, not a survey.
Sediment removal. Mass removed per layer: m = ρ·A·δs with ρ = 2600 kg/m³, so a 20 cm² patch scraped by 0.5 mm is 2.6 g. The brush only lifts the loose layer; the pick chips the hard matrix at δ = 1.4 mm/J · E at the centre (model value).
Why hard blows crack fossils. The cover cushions the shell: the energy reaching it is Ef = E·exp(−h/1.5 mm) and the break probability is P = 1 − exp(−Ef/Ec), Ec = 2.2 J (invented round number). Take the cover off with the pick at low force, never at full swing.
Logarithmic spiral. r(θ) = r0ebθ, W = e2πb (Raup's whorl expansion rate). Here W = 2.0: each whorl is twice as wide as the previous one. Coiling classes (evolute below 1.7, intermediate to 2.6, involute above) are rough [approx].
Tide. h(t) = (R/2)(1 − cos(2πt/T)), T = 12.42 h (the M2 lunar tide), R = 4.5 m [illustrative range]. The platform at 2.6 m is safe until h reaches 2.3 m, which leaves about 2.5 hours; the sim runs 1 minute of tide per second (slider).
Dating. Sedimentary fossils are dated by the rock unit and by index fossils (biostratigraphy), not radiometrically. The Blue Lias of the Dorset coast is Early Jurassic, roughly 200 million years old [approx; check a geological survey source].
Score. Inspect score = 0.6·shape + 0.4·stratigraphy, where shape = 1 − |Wfit − W|/(0.15·W) (clamped) and stratigraphy = coiling type and rock unit both right.
Assumptions. Grid of 160×160 cells (3.9 mm), a single shell, uniform rock, no real fracture mechanics, no wave action on the slab, no sample collection rules. This is a virtual exercise: real fossil hunting means tide tables, staying away from unstable cliffs, local codes and permission to collect.
Sources. Raup, D. M. (1966) on ammonoid coiling parameters [to verify the exact citation]; standard tidal harmonic theory; Jurassic Coast stratigraphy from public geological survey summaries [to verify]. No numbers are quoted from a specific study.
Made with Blender models and Three.js.