Interior of earth
Internal Structure of the Earth
Exploring the layers, composition, and seismic discontinuities that define our planet's interior architecture.
1Introduction
The Earth is not a homogeneous solid sphere but a differentiated body composed of several distinct layers. This layered structure is the result of planetary differentiation early in Earth's history, where denser materials sank to the center while lighter materials rose to the surface.
Our understanding of the Earth's interior comes primarily from seismic waves generated by earthquakes. As these waves travel through the Earth, they change speed and direction depending on the density and state of the material they pass through, allowing scientists to map the interior.
Hover over the model
Hover your mouse over the different sections of the Earth model to see detailed information about each layer.
2The Crust
The crust is the outermost solid layer of the Earth. It is thin, brittle, and forms the surface on which we live. It constitutes less than 1% of Earth's volume.
| Feature | Oceanic Crust | Continental Crust |
|---|---|---|
| Composition | Basaltic (Mafic) | Granitic (Felsic) |
| Density | ~3.0 g/cm³ | ~2.7 g/cm³ |
| Thickness | 5–10 km | 30–70 km |
| Age | Younger (<200 Ma) | Older (up to 4 Ga) |
| Key Elements | Iron, Magnesium, Calcium | Silicon, Oxygen, Aluminum |
Sial and Sima
Historically, the continental crust is referred to as SIAL (Silicon + Aluminum) and the oceanic crust as SIMA (Silicon + Magnesium).
3The Mantle
The mantle makes up about 84% of Earth's volume. It is a silicate rocky shell extending from the base of the crust to the core-mantle boundary.
Lithospheric Mantle: The rigid upper part fused with the crust, forming tectonic plates.
Asthenosphere: Located below the lithosphere (approx. 100-700 km depth). It is ductile and mechanically weak, allowing plate tectonics to occur. Partial melting here generates magma.
Extending from 660 km to 2,900 km, this layer is solid but deforms very slowly over geological time. Pressure is extremely high here. It is the source of some deep-focus earthquakes.
A mysterious zone approximately 200 km thick at the base of the lower mantle. It exhibits significant lateral heterogeneity and may be the "graveyard" of subducted tectonic slabs.
4The Core
The core is the densest part of the Earth, composed primarily of iron and nickel. It is divided into two distinct physical states.
| Property | Outer Core | Inner Core |
|---|---|---|
| State | Liquid | Solid |
| Depth | 2,900 – 5,150 km | 5,150 – 6,371 km |
| Seismic Waves | S-waves do not pass through | P-waves speed up significantly |
| Temperature | 4,000 – 6,000 °C | ~5,400 – 6,000 °C |
| Function | Generates Earth's Magnetic Field | Controls rotation speed of Earth |
Geomagnetism
The liquid outer core convects as heat escapes to the mantle. This motion, combined with the Coriolis effect from Earth's rotation, generates the geodynamo, which creates our planet's magnetic field.
5Major Discontinuities
Discontinuities are boundaries where seismic wave velocities change abruptly due to changes in density or phase.
| Discontinuity Name | Boundary Between | Depth (approx.) | Key Characteristics |
|---|---|---|---|
| Conrad | Upper & Lower Crust | 15–20 km | Separates granitic and basaltic layers. |
| Mohorovičić (Moho) | Crust & Mantle | 30–70 km | P-wave velocity jumps to ~8 km/s. |
| Repetti | Upper & Lower Mantle | 660 km | Transition zone boundary; phase change. |
| Gutenberg | Mantle & Core | 2,900 km | S-waves stop; P-waves slow down. |
| Lehmann | Outer & Inner Core | 5,150 km | Discovered by Inge Lehmann; solid core. |
6Comparative Overview
| Layer | Thickness (km) | Volume (%) | Mass (%) | Main Composition |
|---|---|---|---|---|
| Crust | 0–70 | <1% | 0.5% | Silicates (Si, O, Al) |
| Mantle | 70–2,900 | 84% | 67% | Silicates (Fe, Mg) |
| Core | 2,900–6,371 | 15% | 32.5% | Iron (Fe), Nickel (Ni) |
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