Question

composition thickness/depth and state of matter of crust mantle outer core and inner core

Answer 1

Below are the four main concentric layers of the Earth with typical thickness/depth, composition, and physical state.

1) Crust
- Thickness/depth: oceanic crust ~5–10 km; continental crust ~30–70 km; average crustal thickness ~35 km. The crust ends at the Moho (Mohorovičić discontinuity).
- Composition: igneous, metamorphic and sedimentary rocks. Oceanic crust is mafic (basalt/gabbro); continental crust is more felsic to intermediate (granite, schist, gneiss).
- State of matter: solid, rigid rock (part of the lithosphere).

2) Mantle
- Thickness/depth: ~2,885 km thick, from Moho (~35 km on average) down to the core–mantle boundary (CMB) at ~2,890–2,900 km depth.
- Composition: dominantly ultramafic peridotite (olivine, pyroxenes, garnet, and at depth bridgmanite and ferropericlase); composition varies with depth and phase changes in minerals.
- State of matter: overall solid rock that behaves plastically/viscously on geological timescales and convects. The uppermost mantle plus crust form the rigid lithosphere; the underlying asthenosphere is mechanically weaker and partly ductile (and may contain small amounts of melt).
- Temperatures/density (approx): ~500°C near the top to ~3,000–4,000+°C near the CMB; densities ~3.3–5.6 g/cm3.

3) Outer core
- Thickness/depth: ~2,260 km thick, from the CMB (~2,890–2,900 km depth) down to the inner-core boundary (~5,150 km depth).
- Composition: mainly liquid iron with nickel and some lighter elements (S, O, Si, H, C).
- State of matter: liquid; convecting metallic fluid that generates the geomagnetic field (geodynamo).
- Temperatures/density (approx): ~4,000–6,000 K; densities ~9.9–12.2 g/cm3.

4) Inner core
- Thickness/depth: radius ~1,220 km (extends from ~5,150 km depth to Earth’s center at ~6,371 km).
- Composition: primarily iron with nickel and minor light elements.
- State of matter: solid (high pressure keeps it solid despite very high temperature).
- Temperatures/density (approx): ~5,400–6,000+ K; densities ~12.8–13.1 g/cm3.

Key seismic boundaries: Moho (crust–mantle), Gutenberg discontinuity (mantle–outer core, ~2,890 km), Lehmann discontinuity (outer core–inner core, ~5,150 km).