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A
The study of ocean currents
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B
The theory that Earth's lithosphere is divided into large plates that move slowly over the mantle, causing earthquakes, volcanoes, mountain building, and continent drift
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C
How rivers form
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D
Climate patterns
Why this is the answer
Plate tectonics is the unifying theory of Earth's geological processes. Earth's lithosphere (crust + upper mantle) is broken into ~15 major plates (and many smaller ones) that move slowly (cm/year) over the asthenosphere (semi-fluid upper mantle). Plate boundary types: (1) DIVERGENT — plates move apart; new crust forms; mid-ocean ridges (e.g., Mid-Atlantic Ridge); continental rifts (e.g., East African Rift); produces shallow earthquakes and basaltic volcanism; (2) CONVERGENT — plates collide; types depend on what collides: (a) oceanic-oceanic: subduction zone, volcanic island arcs (e.g., Japan, Aleutians); (b) oceanic-continental: subduction, coastal mountain ranges with volcanoes (e.g., Andes, Cascades); (c) continental-continental: mountain building, no subduction (e.g., Himalayas formed by India-Asia collision); produces deep earthquakes and explosive volcanism; (3) TRANSFORM — plates slide past each other; major earthquakes (e.g., San Andreas Fault in California). Evidence for plate tectonics: (1) Continental jigsaw fit (Africa-South America); (2) Matching fossils across continents; (3) Matching rock formations and ages; (4) Mid-ocean ridges and seafloor spreading; (5) Magnetic stripes on ocean floor showing reversals; (6) Earthquake and volcano distribution; (7) GPS measurements of plate motion. Driving force: convection currents in the mantle from heat (radioactive decay, primordial). Pangaea: supercontinent ~250 million years ago, broke up into current continents. Earthquakes: caused by stress release along faults; measured by Richter or moment magnitude scale. Volcanoes: form where magma reaches surface.
Source: ASVAB Science — Plate Tectonics