PLATE VI
Sedimentary layers expose ~2 Gyr of deposition. Each band tells of a sea, a desert, a delta.
Earth is a layered, slow-cooking heat engine, and the stones at our feet are its receipts. This atlas traces the science of rocks, time, and the moving plates beneath us.
Earth's interior is known mostly through seismic waves. P-waves (compressional) travel through everything; S-waves (shear) cannot pass through liquids. A near-total S-wave shadow at 103°–142° from a quake locates the molten outer core.
Wegener (1912) noted the puzzle-piece fit of the Atlantic coasts. Hess (1962): the seafloor spreads. Vine, Matthews, Morley (1963): magnetic stripes record reversals. Wilson (1965): transform faults complete the picture.
Today: ~15 major + several dozen minor plates, moving 1–10 cm/yr. Three boundary types — divergent, convergent, transform — generate most of Earth's geological activity.
A given mineral grain may visit each compartment several times across hundreds of millions of years. Zircons from Western Australia preserve ages back to 4.4 Ga — older than the oldest known rock.
Two strategies: relative (this is older than that) and absolute (this is 2.45 Gyr old).
Relative dating uses superposition (Steno's law), original horizontality, cross-cutting relationships, and inclusions. Reliable for sequence; silent on years.
Absolute dating uses radioactive decay. Different isotopes for different timescales:
Sedimentary layers expose ~2 Gyr of deposition. Each band tells of a sea, a desert, a delta.
SiO2. Trigonal. Hardness 7. Most abundant in the continental crust.
(K,Na,Ca)AlSi3O8. ~60% of crust by volume.
(Mg,Fe)2SiO4. Mantle's main mineral; gem peridot.
Single-chain silicate; augite, diopside, jadeite.
Sheet silicate; biotite, muscovite. Perfect cleavage in one plane.
CaCO3. Limestone, marble. Rhombohedral cleavage.
NaCl. Cubic. Evaporite mineral. Sets seasoning.
C in cubic close-packing. Hardness 10. Forms ≥150 km depth.
1726–97. Deep time. "No vestige of a beginning, no prospect of an end."
1799–1847. Lyme Regis fossils; ichthyosaur, plesiosaur, pterosaur.
1797–1875. Uniformitarianism in Principles of Geology.
1880–1930. Continental drift, 1912; vindicated decades later.
1888–1993. Discovered the solid inner core via P-wave shadows, 1936.
1920–2006. Mapped the global mid-ocean ridge system.
1906–69. Seafloor spreading, 1962. Trinity-launched the plate revolution.
b. 1940. Ir anomaly; K-Pg impact hypothesis.
Niels Steno states stratigraphic principles.
Hutton sees Siccar Point's angular unconformity.
William Smith publishes the first geological map of England.
Lyell's Principles — uniformitarianism.
John Phillips coins Paleozoic, Mesozoic, Cenozoic.
Wegener proposes continental drift.
Lehmann's inner-core discovery.
Hess's seafloor spreading paper.
Plate tectonics synthesized — Le Pichon, Morgan, McKenzie.
Alvarez et al. propose K-Pg impact.
Crutzen popularizes "Anthropocene".
Anthropocene formally rejected as epoch by ICS — but accepted as event.
Mw = ⅔ log(M0) − 6.07. Largest recorded: Valdivia, Chile 1960, Mw 9.5. ~500,000 detectable per year.
VEI 0–8. Tambora 1815 (VEI 7) caused "year without a summer." Yellowstone (VEI 8) last erupted 640 ka.
Sumatra 2004: ~230,000 dead. Tōhoku 2011: ~20,000. Speed in deep ocean ~700 km/h.
Rainfall, seismic shaking, slope angle, lithology. Vajont, Italy, 1963: 2,000+ dead.
Dissolution of limestone/dolomite. Florida, Yucatán, China.
Tunguska 1908, Chelyabinsk 2013. K-Pg impactor: ~10 km Chicxulub bolide, 66 Ma.
Surface average. ~15 °C/km in stable cratons; up to ~50 °C/km at ridges.
Seismicity scales as power law. b ≈ 1: each unit of M reduces frequency tenfold.
Grain settling speed in fluid. Sets sorting in sedimentary deposits.
"The result, therefore, of our present enquiry is, that we find no vestige of a beginning, no prospect of an end."— James Hutton, Theory of the Earth, 1788
Crutzen and Stoermer popularized "Anthropocene" in 2000. Twenty-three years later, after extensive debate over a candidate Global Boundary Stratotype Section and Point (GSSP), the International Commission on Stratigraphy declined to ratify it as a formal epoch. It survives as a recognized "event."
Either way the signal is unambiguous: ¹⁴C from atomic-bomb testing, plutonium isotopes, plastics, fly ash, novel radionuclides, ratios of nitrogen and phosphorus in soils. Future stratigraphers — if any — will read this layer cleanly.
Li, Co, Ni, Cu, REEs for the energy transition. Mapping deposits and recycling closed-loop.
Whole-mantle plumes (Iceland, Yellowstone) increasingly visualized. Subducted slabs traced to CMB.
mm-precision crustal deformation across plate boundaries; transient slow-slip events.
Cryogenian glaciations; what triggered onset and termination?
Enhanced rock weathering as CDR; basalt CO₂ mineralization (CarbFix).
Perseverance, InSight, Tianwen-1: regolith, seismicity, ancient hydrology.
Plus the BBC's "Earth Story" with Aubrey Manning (1998) on YouTube — still the best long-form survey.