The internal structure of the Earth

The Earth is composed of several distinct layers, each with unique properties that contribute to geological processes.

Layers of the Earth

• Core - At the centre of the Earth lies the core, divided into two parts:
  • Inner core - A solid sphere primarily made of iron and nickel.
  • Outer core - A liquid layer surrounding the inner core, also composed of iron and nickel.
• Mantle - Surrounding the core is the mantle, a semi-molten rock that moves very slowly.
• Crust - The outermost layer is the crust, a thin shell about 10-70 km in thickness.

The nature of tectonic plates and their composition

The Earth's crust is not a single, continuous layer but is broken into large pieces known as tectonic plates. These plates float on the semi-molten mantle beneath them.

Characteristics of tectonic plates

• Division into plates - The crust is segmented into tectonic plates, which are massive slabs that cover the Earth's surface.
• Types of crust in plates - Tectonic plates are composed of two types of crust:
  • Continental crust - Thicker and less dense.
  • Oceanic crust - Thinner and denser.
• Floating on mantle - These plates rest on the mantle, allowing them to shift and move.

The mechanism behind tectonic plate movement

Tectonic plates are in constant, slow motion due to processes occurring deep within the Earth.

Convection currents in the mantle

• Temperature differences - Within the mantle, some regions are hotter than others, particularly deeper down.
• Rising and sinking motion - Hotter, less dense material in the mantle rises towards the surface. As it nears the top, it cools, becomes denser, and sinks back down.
• Circular flow - This continuous cycle of rising and sinking creates convection currents.
• Plate movement - These convection currents are the primary force causing the tectonic plates to shift.

The types of plate boundaries and their characteristics

Tectonic plates interact at their edges, known as plate boundaries or margins. There are four main types of boundaries, each with distinct features.

Destructive boundaries

• Plate interaction - Occur where two plates move towards each other.
• Oceanic vs. continental - When an oceanic plate meets a continental plate, the denser oceanic plate is pushed beneath the continental plate into the mantle.
• Geological features - This often results in the formation of volcanoes and deep ocean trenches.
• Example - The Indo-Australian plate is being forced under the Philippine plate along the eastern coast of Indonesia.

Collision boundaries

• Plate interaction - Happen when two continental plates move towards each other.
• No subduction - Since both plates are of similar density, neither is forced into the mantle.
• Geological features - The crust is instead folded and forced upwards, forming fold mountains.
• Example - The African and Arabian plates are colliding to form the Atlas Mountains.

Constructive boundaries

• Plate interaction - Found where two plates move away from each other.
• Crust formation - Magma from the mantle rises to fill the gap between the diverging plates, cooling to create new crust.
• Example - The African plate and the Antarctic plate are moving apart at the Southwest Indian Ridge.

Conservative boundaries

• Plate interaction - Occur where two plates slide past each other sideways or move in the same direction at different speeds.
• No creation or destruction - Unlike other boundaries, crust is neither created nor destroyed here.
• Example - The Caribbean plate is moving past the South American plate along the eastern Caribbean islands.