Key Points

Direct information about the Earth's interior comes from surface rocks, materials from mining and deep drilling projects, and analysis of molten magma from volcanic eruptions.

Indirect sources provide most of our knowledge and include the analysis of meteors, gravitation, magnetic fields, and most importantly, seismic waves from earthquakes.

The focus, or hypocentre, is the point within the Earth where energy is released during an earthquake. The epicentre is the point on the surface directly above the focus.

Earthquake waves are of two main types: body waves, which travel through the Earth's interior, and surface waves, which travel along the surface and are the most destructive.

P-waves are the fastest body waves and travel like sound waves. They can pass through solid, liquid, and gaseous materials.

S-waves are slower body waves that can only travel through solid materials. This property helps scientists understand the structure of the Earth's core.

A shadow zone is an area on the Earth's surface where seismographs do not record earthquake waves. The large shadow zone of S-waves indicates the existence of a liquid outer core.

Earthquakes are measured by magnitude using the Richter scale (0-10), which relates to energy released, and by intensity using the Mercalli scale (1-12), which assesses visible damage.

The crust is the outermost solid part of the Earth. The continental crust is thicker (about 30 km) compared to the thinner oceanic crust (about 5 km).

The mantle lies below the crust and extends to a depth of 2,900 km. Its upper portion contains the asthenosphere, a weaker zone that is the main source of magma.

The lithosphere is the rigid layer composed of the crust and the uppermost part of the mantle. All natural earthquakes take place in the lithosphere.

The innermost layer is the core, with a liquid outer core and a solid inner core. It is made of heavy materials, mainly nickel and iron, and is called the 'nife' layer.

Major volcano types include Shield volcanoes (fluid basalt lava), Composite volcanoes (viscous lava and ash), Calderas (highly explosive and collapse on themselves), and Flood Basalt Provinces (large outpourings of fluid lava).

The Deccan Traps in India are a large flood basalt province, formed by highly fluid lava that flowed for long distances, covering thousands of square kilometers.

When magma cools and solidifies within the Earth's crust, it forms intrusive landforms. These include batholiths, lacoliths, sills (horizontal), and dykes (vertical).