The Earth's shell is broken into drifting plates — and the sea floor itself is a tape recorder of the drift. New crust is minted at a mid-ocean ridge and carried outward on both sides; as the planet's magnetic field flips, each fresh band freezes in the polarity of its birth, laying down symmetric magnetic stripes that mirror across the ridge. Read a stripe's distance against the age of the reversal that made it and you read the spreading rate. Down the center, data flows: the reversals go in, the engine spreads the floor, the rate comes out. The blue team builds it; the red team tries to break it.
source Vine, F. J. & Matthews, D. H., "Magnetic Anomalies over Oceanic Ridges," Nature 199, 947–949 (1963) — doi.org/10.1038/199947a0; on Wegener (1912) continental drift. Rendered, not quoted.
Sea floor is made at the ridge axis and moves away symmetrically. A reversal at age t is now frozen into crust that sits at distance = rate × t on both flanks — so the stripe pattern is a mirror image across the ridge (the Vine–Matthews evidence). Older floor lies farther out; the age grows monotonically with distance.
For the current rate, the stripe each reversal painted:
| chron | pol | age Myr | dist km |
|---|
Wegener (1912) saw the continents fit like torn paper but had no engine; Vine & Matthews (1963) supplied it — sea-floor spreading, proven by the symmetric magnetic stripes, the rate read straight off the stripe width.
What drives it is buoyancy in the mantle: the same density floating that the-isostasy uses to float a crust on its root, here lifting hot rock at the ridge and pulling cold slabs down at the trench. Each sphere is the next one's premise.
The blue team's live check: recompute the stripe model and confirm it still records spreading — stripes symmetric about the ridge, age rising outward, 20 km / 1 Myr giving 2 cm/yr. If red makes the stripes asymmetric, this badge is where it shows.
The tape's clock is the geomagnetic polarity timescale: dated flips of the Earth's field. The youngest band, born now, holds today's Normal polarity (the Brunhes chron); each older band alternates. These ages are what the ridge feeds outward.
| chron | reversal age (Myr) | polarity |
|---|---|---|
| Brunhes | 0.00 – 0.78 | Normal |
| Matuyama | 0.78 – 2.58 | Reversed |
| Gauss | 2.58 – 3.60 | Normal |
| Gilbert | 3.60 – 5.33 | Reversed |
Feed these reversals into the ridge below and watch where each stripe lands.
Distance a stripe of age t reaches: rate × 10 × t km (1 cm/yr = 10 km/Myr), mirrored on both flanks.
Change the rate — every stripe distance is rate × age, computed on the spot, never looked up. The two flanks are drawn from the same numbers, so they mirror.
What the machine produces, proven: from stripe distance and reversal age it returns the spreading rate (a stripe 20 km out from a 1-Myr reversal = 2 cm/yr), the symmetric-stripe pattern that is the Vine–Matthews proof, and the hard ceiling — no sea floor older than ~180–200 Myr, because it is recycled at subduction zones while continents endure.
The blue team's witness (left) confirms the record holds live; the red team (right) tries to erase it. Global area conservation — ridge creation balancing trench destruction — is real but not asserted here AMBER.
The model also assumes a constant rate between reversals; real half-rates drift and jump, ridges jump, and asymmetric spreading happens. The tape is a clean recorder of that the floor spread — a noisier witness to exactly how fast at every instant.
"Wegener's drift was accepted in his lifetime." Cut. Rejected for ~50 years — he had no mechanism; vindicated only by sea-floor spreading in the 1960s.
"The continents plow through the sea floor." Cut. Wegener's mechanism was wrong; whole plates (crust + lithospheric mantle) move together, new floor minted at ridges.
"Only Vine & Matthews saw it." Kept, corrected. Lawrence Morley reached the same idea independently in 1963 and was refereed away — it is the Vine–Matthews–Morley hypothesis.
The red team's move: stretch the far-side stripes so they no longer mirror the near side — a floor that spread unequally and unrecorded. The blue team's witness (window 7) is watching.
Break the symmetry and the pattern is no longer a spreading record — the witness recomputes, finds the flanks disagree, and turns red. Nothing is faked; the attack is real and it is caught.