PLATE TECTONICS: PROCESSES AND LANDFORMS

From the deepest ocean trench to the tallest mountain, plate tectonics explains the features and movement of Earth’s surface in the present and the past.

Plate tectonics is a scientific theory that explains how major landforms are created as a result of Earth’s subterranean movements. The theory, which solidified in the 1960s, transformed the earth sciences by explaining many phenomena, including mountain building events, volcanoes, and earthquakes.

Introduction to the Chapter – Plate Tectonics and Landforms

Structure of the Earth

The earth is an almost spherical body approximately 6400km in radius. It is made up of three concentric layers: Crust, mantle, core.

CROSS SECTION OF THE EARTH

WHAT’S BELOW US?

1. The Crust – is the thinnest outer most layers on the surface averaging 35km thick beneath the continents but only 6km under the oceans. It is formed largely of igneous rocks. The crust is of two types:

1. Oceanic Crust
2. Continental Crust

Differences between the Oceanic and the Continental Crust

Feature	Oceanic Crust	Continental Crust
Depth of crust	Thin (average of 6km)	Thick (average 35km-40km)
Age	Young (less than 200 million years old)	Older (more than 3500 million years old)
Rock Density	Heavy	Light
Rock Type	Limited number Rich in Silica and magnesium (SIMA) sometimes called basaltic rocks.	Great variety Rich in Silica and Aluminum (SIAL) sometimes called Granite rocks.
Structure	Simple Layered	Complicated structure e.g. Folds

Major Discontinuities in The Earth’s Structure

• Mohorovicic discontinuity – the boundary surface between the earth’s crust and the mantle, lying at a depth of about 10–12 km under the ocean bed and 40–50 km under the continents.
• Gutenberg discontinuity – occurs within Earth’s interior at a depth of about 2,900 km below the surface, where there is an abrupt change in the seismic waves (generated by earthquakes or explosions) that travel through Earth

A CROSS SECTION OF THE CONTINENTAL MARGIN

The continental margin has 3 components:

• 1. Continental Shelf – this is a gently sloping submarine plain found at the edge of a continent and is less than 200m deep.
  2. Continental Slope – is a slope which lies at the edge of the continental shelf and continental rise.
  3. Continental Rise – occurs adjacent to some of the larger continents and represents sediments deposited at the base of the slope.

Activity 1: Table Completion – Oceanic vs. Continental Crust

Instructions: Fill in the missing details in the table comparing oceanic and continental crust using the provided notes.

Feature	Oceanic Crust	Continental Crust
Depth of crust	Thin (average of 6 km)	_______ (Fill in)
Age	_______ (Fill in)	Older (more than 3500 million years old)
Rock Density	Heavy	_______ (Fill in)
Rock Type	Limited in SIMA, Basaltic rocks	Rich in _______ (Fill in)
Structure	_______ (Fill in)	Complicated structure, includes folds

Activity 2: Short Answer Questions – Structure of the Earth

Instructions: Write short answers (1-2 sentences) for the following questions.

1. What are the three main layers of the Earth?
2. Define the crust and explain its significance.
3. What is the Mohorovicic discontinuity, and where is it located?
4. What is the difference in age between oceanic and continental crust?
5. Name two characteristics that distinguishes oceanic crust from continental crust.

Activity 3: Diagram Labeling – Cross Section of the Earth

Instructions: Label the following parts: Crust, Mantle, Core, Mohorovicic Discontinuity, Gutenberg Discontinuity as per your understanding from the notes/diagrams

Activity 4: Matching Terms and Definitions – Major Earth Features

Instructions: Match the terms in Column A to the correct definitions in Column B.

Column A	Column B
Continental Shelf	A slope that lies between the continental shelf and rise.
Continental Slope	The gently sloping area at the edge of a continent.
Continental Rise	Sediment deposition found at the base of the continental slope.
Mohorovicic Discontinuity	Boundary between Earth’s crust and mantle.