The Earth’s relief. The Earth’s crust. Structure of the Earth. Social Sciences

1. The Earth Crust

The structure of the Earth: 

The Earth has three layers: 

Core: 

• It is the deepest layer. 
• It is divided en two parts: 
  • Inner core – Solid. 
  • Outer core – Liquid. 

Mantle: 

• It is the middle layer. 
• It occupies the 85% of the Earth’s volume. 
• It is made by molten rock (magma). 

Crust: 

• It is the Earth surface and is the thinner layer. 
• It is the 1% of Earth’s volume. 
• It is made by solid rock. 
• The temperature increases with depth (5,000 ºC in the core).

Oceans and continents: 

• 70% of the Earth’s surface is covered by oceans and seas: 

Oceans and continents: 

Continents: 

• They are large land masses. 
• From the largest to the smallest, they are: Asia, Africa, America, Antarctica, Europe and Oceania. 

Oceans: 

• They are large masses of saltwater. 
• From the largest to the smallest, they are: Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern Ocean and Artic Ocean. 

2. What is the Earth’s relief?

Relief: 

• It is made up by all the variations in the elevation of the Earth’s surface. 

Relief can be: 

• Continental – Also, it can be inland or coastal relief. 
• Oceanic. 

Continental relief: 

Inland relief: 

Mountains: 

• They can be isolated or forming mountain ranges. 
• Valleys are low lands between mountains. 

Plateaus: 

• They are high raised plains. 
• There are steep slopes in their borders. 

Plains: 

• They are flat and low areas. 
• They appear near coasts or basins of large rivers. 

Depressions: 

• They are flat and very low areas (even below the sea level). 

Coastal relief: 

• They can be high and rocky (cliffs) or low and sandly (beaches) 

Continental relief: 

Coastal relief: 

• They can be high and rocky (cliffs) or low and sandly (beaches). 
• Gulfs and bays (small gulfs) are where the sea extends inland. 
• Capes and peninsulas are areas of land that extend into the sea. 

Oceanic relief: 

Continental shelf: 

• It is the continuation of a continent. 
• It reachs gradually a depth of 200 m. 
• Continental slope. 
• It is a steep slope that separates the continental shelf and the abyssal plains. 

Abyssal plains: 

• They occupy most of the ocean floor and reach a depth between 3,000 and 7,000 m. 
• There are different forms in the abyssal plains: 
  • Mid – oceans ridges – They are long underwater mountain ranges. Sometimes, they form islands.
  • Ocean trenches – They are long deep cracks. The deepest ocean trench is Challenger Deep (11,000 m) in the Pacific Ocean.

3. Internal forces of relief

Continental drift and tectonic plates

Theory of continental drift: (Wegener)

• Many millions of years ago, there was a super – continent called Pangea. 
• This super – continent broke up and its pieces separated and formed the today’s continents. 

Tectonic plates: 

• The Earth’s crust is divided into great blocks called tectonic plates. 
• This plates slide (continually and very slowly) over the mantle and they can separate or collide. 
• When two plates collide between them, mountain ranges are formed. 

Faults and folds: 

• The boundaries between tectonic plates have a lot of seismic and volcanic activity. 
• The movements of the tectonic plates causes faults and folds: 
  • Folds are created when rocks are flexible.
  • Faults are created when rocks are extremely rigid (then, rocks break up).

Volcanoes: 

• A volcano is a crack in the Earth’s crust. 
• They appear near to the boundaries of the tectonic plates (where the crust is weakest). 

Volcanic eruptions: 

• Magma (molten rock) rises to the Earth’s surface through the vent. 
• During the eruption, lava (name for the magma outside the volcano), ash and gases are rejected through an opening in the volcano called crater. 
• Lava and rock accumulate around the volcano and form a cone. 

Earthquakes: 

• They are violent movements of the Earth’s crust. 
• They occur near the boundaries of the tectonic plates. 

Earthquake: 

• Energy is released in seismic waves. 
• The hypocentre is the point under the Earth’s surface were earthquake is originated.
  
• The epicentre is the closest point on the Earth’s surface to the hypocentre (the earthquake is strongest at this point). 
• Earthquakes also can occur in the ocean floor and they can cause a tsunami.

https://www.youtube.com/watch?v=Kg_UBLFUpYQ

4. How does relief change?

Changes in relief: 

Earth’s relief is formed by: 

• Internal forces – Tectonic plates. 
• External forces – Temperatures, water, wind and human action. 

The action of the external forces have three stages: 

• Erosion – Rocks and soil are broken by external agents. 
• Transportation – The eroded material is transported by external agents. 
• Deposition – These materials are deposited in areas in form of sediments. 

Water: 

Rivers: 

• Upper course: 
  • River flow is very strong because of the steep slopes. 
  • Erosion is very strong. 
• Middle course – River transport the eroded materials. 
• Lower course – River deposits sediments. 

Seas and oceans: 

• Seawater hits continually coasts forming cliffs. 
• Seawater carry sediments and deposits them on the coast forming beaches. 

Rainwater and groundwater: 

• It can dissolve some type of rocks (limestone rocks). 
• It can break up some type of rocks (rigid rocks): 
• Water can filter inside these rocks. 
• If this water freezes, it will expand and broke up the rock.

Wind: 

• Winds transport particles of eroded materials and deposits them in another place. 

Living things: 

• Tree roots can break up soils. 
• Some animas dig tunnels and they can break up soils. 

Human beings have a huge influence over the Earth’s relief: 

• Agriculture. 
• Mining. 
• Roads. 
• Reservoirs.

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