The Large Scale Structure of the Earth

The Earth has several layers, each with unique characteristics. The main layers, from the surface to the centre, are the crust, mantle, outer core, and inner core.
The crust is the Earth’s outer skin. It’s a thin layer: 5-70km thick and divided into oceanic and continental crust. The oceanic crust is denser and usually composed of basalts, while the continental crust is less dense, composed predominantly of granitic rock.
Below the crust lies the mantle, divided into upper and lower sections. The mantle is thick, approximately 2,900km deep, and composed mainly of silicate rocks. Its upper part, together with the crust, forms the lithosphere.
The Asthenosphere, a section of the upper mantle located below the lithosphere, is partially molten and allows plate tectonics to occur.
The outer core is primarily composed of liquid iron and nickel, and is approximately 2,200km thick. It creates the Earth’s magnetic field due to its convective motion.
At the Earth’s centre lies the inner core, a solid ball of iron and nickel due to immense pressure despite the high temperatures. It’s about 1,200km in radius.
The interplay between layers and their characteristics drive processes like plate tectonics, volcanic activity, and earthquakes. This dynamic nature helps maintain the Earth as a habitable planet.
Through geological time, the Earth’s structure has continuously changed, and will continue to do so, due to these internal and external processes.

The Theory of Plate Tectonics

Plate tectonics is the theory explaining the movement and interactions of the Earth’s lithosphere plates.
The Earth’s lithosphere is divided into numerous ‘tectonic plates’ that float on the semi-fluid Asthenosphere beneath.
Major types of plate boundaries include: convergent boundaries where plates collide, divergent boundaries where plates separate, and transform boundaries where plates slide past each other.
The movements of these plates can lead to the creation of landforms such as mountains, trenches, volcanoes, and earthquakes.
The Earth’s continents as we see them today were once part of a single supercontinent known as Pangaea due to tectonic movement.
Sea-floor spreading, where new oceanic crust is formed at divergent boundaries and pushes the plates apart, provides evidence supporting the theory of plate tectonics.

Remember, deeper understanding of these points will allow you to answer exam questions more confidently. Revising diagrams and learning definitions for key terms can also enhance your understanding.