Crust_(geology) - Wikiparency

# Crust (geology) ## Microsim (three.js) <div class="microsim-player">  <p class="wt-pending"><strong>Microsim staged, not yet on the CDN.</strong> <code>Crust_%28geology%29.html</code> is built and deploy-ready in <code>Microsims for Dissemination/</code>, but the Netlify project still serves the geometry+spintronics set only. The player is disabled until the deploy lands; the explanatory text below is unchanged.</p>   </div> *Part of the COSMOS earth-and-space hub: the crust is the brittle outer shell that seismology first mapped, where the earthquakes and faults of plate tectonics play out and where seismic tomography still probes the roots beneath mountains.* > The **crust** is Earth's thin, outermost rock layer, resting on the denser mantle below. It comes in two kinds — thick, light continental crust and thin, heavy oceanic crust — and it "floats" on the ductile mantle much as an iceberg floats on water, a balance called *isostasy*. This microsim lets you set the thickness and density of each crust type and watch how high it rides, then switch to a plate-tectonic view where crust is born at spreading ridges and consumed at subduction zones. Adjust the sliders to discover why continents stand above the sea while the ocean floor stays low and young. ## About this microsim The simulation has two scenes. The **Isostasy Cross-Section** is driven by four sliders — **Continental thickness** (40 km, adjustable 20–70), **Continental density** (2.70 g/cm³, 2.55–3.15), **Oceanic thickness** (7 km, 3–15) and **Oceanic density** (2.90 g/cm³, 2.70–3.20) — which set the two crustal blocks floating on the mantle. A **Spreading / subduction rate** multiplier (1.0×, 0.2–3) animates the **Plate Boundaries** scene. Two view buttons switch between the scenes; **Pause ▮▮** freezes the animation, **Reset boundary scene** restarts the moving-plate view, and **Reset to Earth-like defaults** returns every slider to the values above. There are no other hidden controls. ## Related microsims - Seismology — seismic waves reveal the Moho and measure crustal thickness - Earthquake — most quakes nucleate along the plate boundaries shown here - Fault (geology) — transform boundaries slip along crustal faults - Seismic tomography — images the deep crustal roots that isostasy predicts - Stratigraphy — records the layered rocks built upon the crust ## Links (Wikipedia order)  `Abundance_of_elements_in_Earth's_crust` · `Adiabatic_process` · `Allan_Hills_84001` · `Anorthosite` · `Archibald_Geikie` · `Asthenosphere` · `Basalt` · `Cambridge_University_Press` · `Conrad_discontinuity` · `Continental_crust` · `Core–mantle_boundary` · `Cumulate_rock` · `Dwarf_planet` · [[Earth]] · `Earth's_crust` · `Earth's_inner_core` · `Earth's_mantle` · `Earth's_outer_core` · `Earth_and_Planetary_Science_Letters` · `Elements_(journal)` · `Elsevier` · `Encyclopedia_Americana` · `Erosion` · `Far_side_of_the_Moon` · `Feldspar` · `Formation_and_evolution_of_the_Solar_System` · `Geology` · `Geology_of_the_Moon` · `Igneous_rock` · `Impact_crater` · `Internal_structure_of_Earth` · `Io_(moon)` · `Janne_Blichert-Toft` · `Large_low-shear-velocity_provinces` · `Lehmann_discontinuity` · `Lithosphere` · `Lithosphere–asthenosphere_boundary` · `Lithospheric_mantle` · `Lower_mantle` · `Lunar_magma_ocean` · `Lunar_mare` · `Magma` · `Mantle_(geology)` · [[Mars]] · `Martian_meteorite` · `Mercury_(planet)` · `Mid-ocean_ridge` · `Mohorovičić_discontinuity` · [[Moon]] · `Natural_satellite` · `Near_side_of_the_Moon` · `Oceanic_crust` · `Oldest_dated_rocks` · `Olivine` · `Partial_melting` · `Plagioclase` · `Planet` · `Plate_tectonics` · `Protoplanet` · `Pyroxene` · `Silicate_mineral` · `Terrestrial_planet` · `Transition_zone_(Earth)` · `University_of_Arizona_Press` · `Upper_mantle` · [[Venus]] ## Overview The crust is the outermost of Earth's compositional layers, separated from the underlying mantle by the Mohorovičić discontinuity (the "Moho"), where seismic P-wave speeds jump from about 6–7 to 8 km/s. Together with the rigid uppermost mantle it forms the lithosphere, which is broken into tectonic plates riding on the slowly flowing asthenosphere. Continental crust is ancient (locally up to ~4 billion years old), thick and felsic; oceanic crust is young (< ~200 million years), thin and mafic, continuously created at mid-ocean ridges and destroyed at subduction zones. ## The science Two ideas govern the microsim: buoyant equilibrium and plate motion. *Isostasy* applies Archimedes' principle to the crust. A block of thickness $T$ and density $\rho_c$ floating on mantle of density $\rho_m$ settles until it displaces its own weight, standing a height $T\left(1-\rho_c/\rho_m\right)$ above the mantle. Lighter or thicker crust rides higher — the reason continents form high land while ocean basins lie low. In the Airy model, high topography is supported by a deep crustal *root*: a mountain of height $h$ needs a root of depth $r = h\,\frac{\rho_c}{\rho_m-\rho_c}.$ With $\rho_c = 2.7$ and $\rho_m = 3.3\ \mathrm{g/cm^3}$, $r \approx 4.5\,h$ — every kilometre of mountain hides about 4.5 km of root. | Property | Continental | Oceanic | |---|---|---| | Composition | felsic (granitic) | mafic (basaltic) | | Thickness | ~35–40 km | ~7 km | | Density | ~2.7 g/cm³ | ~2.9–3.0 g/cm³ | | Age | up to ~4 Ga | < ~200 Ma | At **plate boundaries** the lithosphere moves: *divergent* boundaries (spreading ridges) make new oceanic crust, *convergent* boundaries consume it by subduction or crumple it in collision, and *transform* boundaries slide past along faults. Slab pull and ridge push, fed by mantle convection, drive rates of roughly 2–15 cm/yr. ## Controls -> what each maps to | Control | Maps to | Range / values | Meaning | |---|---|---|---| | Continental thickness | Thickness of the continental block | 20–70 km (default 40) | Thicker crust rides higher and roots deeper | | Continental density | Density of continental crust | 2.55–3.15 g/cm³ (default 2.70) | Lighter felsic crust is more buoyant | | Oceanic thickness | Thickness of the oceanic block | 3–15 km (default 7) | Sets how the sea floor sits below continents | | Oceanic density | Density of oceanic crust | 2.70–3.20 g/cm³ (default 2.90) | Denser mafic crust rides low and can subduct | | Spreading / subduction rate | Speed of plate-motion animation | 0.2–3× (default 1.0×) | Faster boundaries create/consume crust sooner | | Isostasy Cross-Section | View toggle | button | Shows the floating-block buoyancy scene | | Plate Boundaries | View toggle | button | Shows divergent, convergent and transform types | | Pause ▮▮ | Freeze animation | button | Stops motion to inspect a configuration | | Reset boundary scene | Restart boundary view | button | Returns plates to starting positions | | Reset to Earth-like defaults | Reset sliders | button | Restores the default values above | ## Learning objective Understand how crustal thickness and density set surface elevation through isostatic buoyancy, and how plate boundaries continuously create and destroy Earth's crust. ## Limits and connections The model treats the mantle as an inviscid fluid and ignores flexural rigidity, sediment loading and the thermal subsidence of aging oceanic crust; it also shows only local (Airy-style) compensation, not regional flexure. Real isostasy is imperfect, and those departures are precisely what gravity surveys and seismic imaging measure. ## Poster & source <div class="microsim-fallback">  <p><em>Live microsim · <a href="https://wikitube-3d-microsims.netlify.app/Crust_%28geology%29.html">open full</a> · source: Microsims for Dissemination/COSMOS_microsims/Crust_(geology).html</em></p> </div>  *Built to the [[WT!Three_js_Microsim_Master_Class|three.js Master Class]].*  ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Crust_%28geology%29) : [Wikitube](https://en.wikitube.io/wiki/Crust_%28geology%29) ## Previous hub tags Tree parent: [[Oxygen]]. Legacy hubs: `COSMOS`. --- *Sources: 1 legacy note. Minted wave 1, 2026-07-30 (v1.6 order).*