# Plate Tectonics — Field Guide Canonical URL: https://shipslides.com/d/catalog-science-plate-tectonics Raw viewer URL: https://content.shipslides.com/d/catalog-science-plate-tectonics/raw Category: Science Slides: 13 Updated: 2026-05-17T20:55:47.568Z Tags: catalog, science, plate, tectonics ## Summary Alfred Wegener, a German meteorologist, noticed that the coastlines of South America and Africa fit like puzzle pieces. Matching fossils, glacial deposits, and rock formations on opposite Atlantic shores convinced him: continents move . Key sections include: PLATE TECTONICS; Wegener, 1912; Magnetic stripes, 1960s; The Grand Synthesis, 1967-68; The Plates; Boundaries; Subduction; Collision; Hotspots; Earthquakes. ## Slide Outline 1. PLATE TECTONICS 2. Wegener, 1912 3. Magnetic stripes, 1960s 4. The Grand Synthesis, 1967-68 5. The Plates 6. Boundaries 7. Subduction 8. Collision 9. Hotspots 10. Earthquakes 11. Past Supercontinents 12. Pangaea Ultima 13. Closing ## Slide Transcript ### Slide 1: PLATE TECTONICS - A Field Guide · Slide One of Thirteen - Continents adrift on stone - Earth's lithosphere is fractured into rigid plates that creep, collide, and tear apart over geologic time. ### Slide 2: Wegener, 1912 - 02 · The Heretic - Continental drift — and the laughter that followed - Alfred Wegener, a German meteorologist, noticed that the coastlines of South America and Africa fit like puzzle pieces. Matching fossils, glacial deposits, and rock formations on opposite Atlantic shores convinced him: continents move. - "The Earth's crust ... must be conceived as floating on a viscous substratum." — Wegener, Die Entstehung der Kontinente - His mechanism was wrong (he proposed continents plowing through ocean crust) and geophysicists derided him. He died in 1930 on a Greenland ice expedition, his theory still rejected. - Fig. 1 — Matching fossils and coastlines (red dots: Mesosaurus, Glossopteris) ### Slide 3: Magnetic stripes, 1960s - 03 · The Smoking Gun - The ocean floor records its own history - Sonar surveys mapped a colossal mountain chain running down the middle of every ocean basin — the mid-ocean ridges. Then magnetometers pulled behind ships found something stranger: parallel stripes of normal and reversed magnetism, mirrored on either side of the ridge crest. - Lava erupts at the ridge, freezes magnetic field of the day into the rock - New crust spreads outward — older crust pushed away - Stripes match Earth's known polarity-reversal record - Vine, Matthews & Morley (1963): the ocean floor is a tape recorder. Spreading rates ~ 2-15 cm/yr. - Fig. 2 — Symmetric magnetic stripes flanking a spreading ridge ### Slide 4: The Grand Synthesis, 1967-68 - 04 · The Revolution - From outlaw idea to textbook truth in a decade - By the late 1960s, several lines of evidence converged into one unifying theory: - 1965 — Tuzo Wilson identifies transform faults; proposes "plates" - 1967 — Jason Morgan and Dan McKenzie independently formalize plate motions on a sphere - 1968 — Le Pichon publishes the first global plate model with six plates - 1968 — Isacks, Oliver & Sykes correlate earthquake distributions with plate boundaries - Plate tectonics is to geology what evolution is to biology: a single framework that organizes nearly every observation. It went from heresy to orthodoxy in roughly five years. - Wilson - Morgan - McKenzie - Le Pichon - Synthesis ### Slide 5: The Plates - 05 · Inventory - Seven majors, several minors, all in motion - The lithosphere is broken into roughly fifteen plates. The seven major ones cover most of the surface; the minors sit at busy intersections. - Major: Pacific, North American, South American, African, Eurasian, Indo-Australian, Antarctic - Minor: Cocos, Nazca, Caribbean, Arabian, Philippine, Juan de Fuca, Scotia - Oceanic crust is thin (~7 km), dense, dark basalt — young (< 200 Ma). - Continental crust is thick (~35 km), light granite — ancient, with rocks up to 4 Ga old. - Fig. 3 — Schematic plate map; red lines = boundaries ### Slide 6: Boundaries - 06 · Three Kinds of Edge - Where plates meet, things happen - Divergent — plates pull apart; magma rises, new crust forms (Mid-Atlantic Ridge, East African Rift) - Convergent — plates push together; one dives under (subduction) or both crumple (collision) - Transform — plates slide past horizontally, neither created nor destroyed (San Andreas) - All the violence Earth offers above the weather — earthquakes, volcanoes, mountain belts, tsunamis — concentrates along these thin lines. - Fig. 4 — Three boundary geometries ### Slide 7: Subduction - 07 · Diving Plates - Where ocean meets continent and loses - Oceanic crust is dense. When it meets continental crust, it bends and dives — typically at angles of 30 to 60 degrees — descending hundreds of kilometers into the mantle. - Trench at the surface (deepest spots in the ocean) - Water released from sinking slab triggers melting above - Magma rises through the overlying plate → volcanic arc - Deep "Wadati-Benioff" earthquakes track the slab down - Examples: the Andes (Nazca ↓ South America), the Cascades (Juan de Fuca ↓ N. America), Japan (Pacific ↓ Eurasia). - Fig. 5 — Subduction-zone cross-section ### Slide 8: Collision - 08 · Mountain Building - India hits Asia · the Himalayas - When two continental plates collide, neither will subduct — both are too buoyant. Instead the crust crumples and stacks, doubling its thickness and rising into mountains. - India broke from Gondwana ~140 Ma ago - Slammed into Asia ~50 Ma ago at unprecedented speed (~15 cm/yr) - Continues pushing north today at ~5 cm/yr - Himalayas still rising at ~1 cm per year - Mt Everest grows taller each year. Erosion shaves it back. The mountain is a balance between tectonic uplift and the patient work of water and ice. - Fig. 6 — Continental collision: India + Eurasia ### Slide 9: Hotspots - 09 · Anomalies - Volcanoes that don't follow the rules - Most volcanism happens at plate boundaries. But Hawaii sits in the middle of the Pacific Plate. Yellowstone sits in the middle of North America. Why? - The leading explanation: mantle plumes — narrow columns of hot rock rising from deep in the mantle, perhaps from the core-mantle boundary 2,900 km down. The plate slides over the stationary plume, creating a chain of progressively older volcanoes. - Hawaii: Big Island (active) → Maui → Oahu → Kauai → Emperor Seamounts (80 Ma) - Yellowstone: hotspot track across Snake River Plain; supereruptions every ~600 ka - Iceland: hotspot superimposed on a mid-ocean ridge - Fig. 7 — Stationary plume, moving plate ### Slide 10: Earthquakes - 10 · Stick and Slip - Stress accumulates · stress releases - Plates don't glide smoothly. They lock against each other, deform elastically, and then fail. The accumulated strain releases in seconds as a rupture propagates along the fault — that's an earthquake. - The San Andreas Fault is the textbook transform boundary, running ~1,200 km up California. The Pacific Plate slides northwest past the North American Plate at ~3-4 cm/yr. Locked sections store decades of strain, then release in M7+ events. - 1906 San Francisco — M7.9, fault offset up to 6 m - 1989 Loma Prieta — M6.9, collapsed Bay Bridge segment - The southern segment hasn't released since ~1857; it is overdue - "It is not if, but when." — USGS, on the next great San Andreas rupture. - Fig. 8 — California's transform boundary ### Slide 11: Past Supercontinents - 11 · Deep Time - The pieces have assembled before - Plate motion runs in cycles. Roughly every 400-600 Myr the continents collect into a single supercontinent, then rift apart and disperse, only to reconvene on the far side of the globe. - Pangaea (~335-175 Ma) — the famous one; broke apart in the Jurassic, opening the Atlantic - Pannotia (~600 Ma) — short-lived, late Precambrian - Rodinia (~1.1-0.75 Ga) — assembled deep in the Proterozoic - Columbia / Nuna (~1.8-1.5 Ga) — even older - Kenorland (~2.7 Ga) — Archean assembly, edges of geologic memory - We can read Pangaea directly from matching coastlines and rocks. Rodinia is reconstructed from paleomagnetic data, mountain belts, and zircon ages — increasingly fuzzy back through time. ### Slide 12: Pangaea Ultima - 12 · Looking Forward - ~250 million years from now - If current motions continue, the continents will reassemble into a new supercontinent in roughly a quarter-billion years. Geologists have proposed several possible configurations: - Pangaea Ultima (Scotese) — Atlantic closes, Americas slam back into Eurasia/Africa - Amasia — continents collect over the North Pole as the Pacific closes - Aurica — both Atlantic and Pacific close; new ocean opens elsewhere - A 2023 study suggests Pangaea Ultima would be hostile to mammals — a hot, dry interior with CO₂ levels driving surface temperatures past mammalian survival limits. Long after we're gone. - Fig. 9 — Possible Pangaea Ultima configuration ### Slide 13: Closing - 13 · References & Further Reading - Continents adrift on stone — go deeper - References - Wegener, A. Die Entstehung der Kontinente und Ozeane (1912/1929) - Vine, F. & Matthews, D. "Magnetic Anomalies over Oceanic Ridges" — Nature (1963) - Wilson, J. T. "A new class of faults and their bearing on continental drift" — Nature (1965) - Morgan, W. J. "Rises, Trenches, Great Faults, and Crustal Blocks" — JGR (1968) - Le Pichon, X. "Sea-Floor Spreading and Continental Drift" — JGR (1968) - Farnsworth et al. "Climate extremes likely to drive land mammal extinction during next supercontinent assembly" — Nature Geoscience (2023) - Watch - YouTube: Plate Tectonics Explained - Overview lectures, animations, documentaries - YouTube: Wegener & Continental Drift - The history of the idea — from heresy to orthodoxy - "The Earth tells its own history in stone. We have only to learn the language." ## Related Decks - [CLIMATE / Earth's thermostat in motion](https://shipslides.com/d/catalog-science-climate) - [Cosmology / 13.8 billion years, briefly](https://shipslides.com/d/catalog-science-cosmology) - [Ecology / Webs of Dependence](https://shipslides.com/d/catalog-science-ecology) - [On the Origin of Species — A Field Notebook](https://shipslides.com/d/catalog-science-evolution)