Built by a geologist

Earth's Structure

Earth's Structure If you could slice Earth in half like an apple, you'd see it has distinct layers — each with different composition, temperature, and physical properties. The Major Layers The Crust The outermost layer — the thin skin we live on. - Continental crust : 30–70 km thick, made mostly of granite-like rocks felsic . Average density 2.7 g/cm³ - Oceanic crust : Only 5–10 km thick, made mostly of basalt mafic . Average density 3.0 g/cm³ - The crust makes up less than 1% of Earth's total volume The Mantle Below the crust, extending to 2,900 km depth. - Makes up about 84% of Earth's volume - Composed of silicate rocks rich in iron and magnesium ultramafic - The upper mantle to 670 km includes partially molten rock - The lower mantle is solid but can flow very slowly over millions of years The Core The innermost layers — extremely hot and dense. - Outer core 2,900–5,150 km : Liquid iron and nickel. This flowing metal generates Earth's magnetic field - Inner core 5,150–6,371 km : Solid iron and nickel. Temperature reaches 5,400°C — as hot as the surface of the Sun Lithosphere vs. Asthenosphere For understanding plate tectonics, geologists divide the outer Earth differently: - Lithosphere : The rigid outer shell crust + uppermost mantle , 100 km thick. This is what breaks into tectonic plates - Asthenosphere : The partially molten, ductile layer below 100–300 km . Plates "float" and slide on this layer How We Know No one has ever drilled to the mantle. We know Earth's interior structure from: - Seismic waves — Earthquakes send waves through Earth that bend and reflect off layer boundaries - Meteorites — Iron meteorites may represent the cores of destroyed protoplanets, giving clues to Earth's core composition - Density calculations — Earth's overall density 5.5 g/cm³ is much higher than surface rocks 2.7 g/cm³ , proving the interior must be very dense