Planet Earth of Life: The Earth’s Layers

Objectives

At the end of the session the students should be able to:

1. Show and explain the layers of the Earth.

2. Show through example the explanation on how the three major rock types are formed and how rock cycle works.

3. Can identify and explain the Soil layer.

Earth’s Layer

• Geologists believe the earth is neither liquid nor solid all the way through.  

• It is a made up of different layers.  

1. Crust

2. Mantle

3. Outer core

4. Inner core

Crust

• The Earth's outermost surface which makes up 1% of the Earth.

• Relative to its size, Earth's crust is about as thin as an apple's skin.

• It is relatively light and brittle so that most earthquakes occur in this layer.

• The crust of the Earth is broken into many pieces called plates.

Types of Crust 

1. Oceanic crust

2. Continental crust

Mantle 

• Largest layer of the Earth located below the crust

• Although the mantle does have a thin solid layer at the top, it is composed almost entirely of magma - molten rock inside the earth.  

• Magma undergoes a slow circular flow in the mantle, a result of convection currents driven by the great temperature difference between the top and the bottom of the mantle (1600º F near the top and 4000º F at the bottom).  

Convection Currents 

• Convection currents are caused by the very hot magma at the deepest part of the mantle rising to the top, then cooling and sinking to the bottom, and repeating the cycle over again.  

• The convection currents inside the mantle cause the solid lithospheric plates above it to move. 

Outer Core 

• It is about 2,200 km thick, and is made of nickel and iron in the liquid state.  

• Pressures and temperatures in this layer are greater than the mantle and crust.

• When the Earth rotates, the liquid in the outer core spins creating the Earth's magnetic field. 

Inner Core 

• Solid innermost layer of the Earth.

• It is about 1,250 km thick and has the greatest pressures, temperatures, and the most dense materials of any layer.  

Rock 

• In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids (mineral-like substance).

• The Earth's outer solid layer, the lithosphere, is made of rock. 

• The scientific study of rocks is called petrology. 

Types of Rock 

1. Igneous Rock

2. Sedimentary Rock

3. Metamorphic Rock 

Igneous Rock 

• These are rocks that solidified directly from molten magma.

• Examples: Granite

Basalt

Pumice

Flint

Sedimentary Rock 

• These are formed when igneous rocks are eroded as sediment under the sea. 

• Examples: Limestone

Chalk

Sandstone 

Metamorphic Rock 

• These are made up of igneous and sedimentary rocks of all ages which have been subjected to intense pressure. 

• Examples: Slate

Marble

Quartzite 

Rock Cycle 

• This occurs when igneous rock is buried deep within Earth and is exposed to great heat and pressure. As well, metamorphic and sedimentary rocks may be exposed at the surface of Earth and be subject to weathering and erosion hence creating new material for sedimentary rocks. 

Soil

Soil covers much of the land on Earth.

It is made up of minerals (rock, sand, clay, silt), air, water, and organic (plant and animal) material.

Soil is formed slowly as rock erodes into tiny pieces near the Earth's surface.

Soil Horizons (Layers)

Soil is made up of distinct horizontal layers; these layers are called horizons.

They range from rich, organic upper layers to underlying rocky layers.

Soil Horizons

1. O Horizon

The top, organic layer of soil, made up mostly of leaf litter and humus (decomposed organic matter).

2. A Horizon

The layer called topsoil.

It is made up of humus (decomposed organic matter) mixed with mineral particles.

3. E Horizon

This eluviation (leaching) layer is light in color. 

It is made up mostly of sand and silt, having lost most of its minerals and clay as water drips through the soil (in the process of eluviation).

4. B Horizon

Also called the subsoil.

It contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate) that it receives from layers above it when mineralized water drips from the soil above.

5. C Horizon

Also called regolith. It consists of slightly broken-up bedrock.

Plant roots do not penetrate into this layer and very little organic material is found in this layer.

6. R Horizon

The unweathered rock (bedrock) layer that is beneath all the other layers.