# Vocabulary Back to [[Expanding Earth and Plate Tectonics]] ## Plate tectonics - **Lithosphere:** the rigid outer shell, made of crust plus the uppermost cold mantle. It is about 100 km thick under old ocean. The map colors *oceanic lithosphere* by age. - **Asthenosphere:** the hotter, weaker mantle below the lithosphere, on which plates move. - **Mid-ocean ridge / spreading center:** where plates pull apart and new ocean crust forms. These are the "zones of expansion" in the post. Examples are the Mid-Atlantic Ridge and the East Pacific Rise. - **Subduction zone:** where one plate (usually old, dense oceanic lithosphere) sinks under another into the mantle. Its surface trace is a deep-sea **trench**, such as the Mariana, Japan and Peru–Chile trenches. - **Ring of Fire:** the volcanic and earthquake belt around the Pacific, built along its subduction zones. - **Wadati–Benioff zone:** a dipping band of earthquakes, down to about 700 km, that tracks a sinking slab. - **Slab / slab pull:** the subducting plate, and the pull its weight exerts on the rest of the plate. - **Craton:** an old, stable continental core with a deep keel (Nikolov says 150–300 km). - **Accretionary complex:** sediments and crust scraped off a subducting plate and stacked onto the overriding plate. - **Ophiolite:** a slice of ocean crust and upper mantle pushed up onto land. - **Ridge migration:** ridges move over time. That is how a ridge can surround Africa or Antarctica without any expansion. - **Conjugate flank:** the matching crust on the other side of a ridge. In the Pacific, many conjugate flanks are missing because they were subducted. - **Back-arc basin:** small ocean basins that open behind subduction zones (e.g., the Mariana Trough). ## Dating and imaging - **Magnetic anomalies / isochrons:** stripes of normal and reversed magnetization in the seafloor. Lines of equal age (isochrons) are drawn from them. - **Ma / My:** millions of years ago / millions of years. The post's "180 My" means 180 Ma. - **Seismic tomography:** a CT-scan-like image of the mantle built from earthquake waves. Cold slabs show up as fast anomalies. - **UHP (ultra-high-pressure) metamorphism:** rocks formed at more than about 90 km depth (marked by **coesite** or diamond) and later exhumed. - **Radiolarian chert:** rock made of microscopic silica skeletons, which forms slowly on the deep ocean floor. - **Hadean zircon:** zircon crystals over 4 billion years old. Their oxygen isotopes record contact with liquid water. ## Geodesy and physics - **Space geodesy:** precise positioning by GPS/GNSS, VLBI, satellite laser ranging and DORIS. - **ITRF (International Terrestrial Reference Frame):** the global coordinate frame that these measurements define. Wu et al. 2011 tested the radius against it. - **Paleomagnetic radius test:** comparing ancient magnetic latitudes across distances on one continent to estimate Earth's past radius. - **Surface gravity, g = GM/R²:** with constant mass, a smaller Earth has *higher* g. Expansion with *lower* past g therefore needs mass gain. - **Paleogravity:** past surface gravity. It is not a mainstream measured quantity; Hurrell and Nikolov estimate it from animal bones. ## Expanding Earth terms - **Expanding Earth / Expansion Tectonics:** the idea that Earth's radius has grown and that oceans formed as the crust split, with no subduction. It is associated with Hilgenberg (1933), Carey and Maxlow. - **Panthalassa / Tethys:** the global ocean and the equatorial ocean of the Paleozoic–Mesozoic in the plate-tectonic view. Expanding Earth denies they existed.