Outer core
Topic: Interior of the Earth: Earthquakes, Volcanoes and the Layered Earth · NCERT: Class 11, Ch 3 "Interior of the Earth"
Meaning
The outer core is a liquid layer of molten iron and nickel. It lies between about 2,900 km and 5,150 km below the surface. We know it is liquid because S-waves, which can only travel through solids, stop when they reach it. P-waves pass through but slow down and bend. Heat and the earth's spin keep the liquid metal moving. This moving metal works like a dynamo (a machine that makes electricity) and produces the earth's magnetic field. This is called the geodynamo.
Example
Seismographs more than 105° from an earthquake's epicentre record no S-waves. This S-wave shadow zone covers a little over 40 per cent of the earth's surface, and the liquid outer core causes it.
Don't confuse with
- Inner core: same iron-nickel material, but solid, from 5,150 to 6,371 km. Huge pressure keeps it solid.
- Asthenosphere: a weak, partly molten zone in the upper mantle, down to about 400 km. It is not the core.