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Layers of the Earth – Grade 7 Science Worksheets

Earth’s Structure

What are the four different layers of the earth?

Geologists have observed vibrations (seismic waves) made by earthquakes to understand the structure of the earth’s inside. They found that it is divided into these distinct layers: the crust, the mantle , outer Core and the inner core.

Crust

Crust is the top or the outermost layer. It is very solid, and also the thinnest of all layers, only about 5000m thick under the oceans and about 30000m of thickness under the landmasses.

Mantle

It is made of two parts, upper and lower, the thick upper layer is made of extremely hot, semisolid liquid rock pattern and is located directly below the crust and is about 2,900 km thick.

Outer core

The outer core is the only layer which is a liquid layer: an ocean of mostly thoroughly liquid iron and nickel. It is about 1,800 to 3,000 miles below the surface and about 2,300 km thick.

Inner core

An extremely hot layer, solid ball of iron and nickel at the center of the earth. It is 3,000 to 3,960 miles below the surface and about 1,200 km in diameter.

Lithosphere

This layer is made up of the crust and a very small lining of the upper mantle; it is divided into many slowly moving plates of solid structure that has the continents and oceans above it.

Asthenosphere

The upper mantle makes the plates of the lithosphere move on this hot, liquid magma right below the lithosphere.

How deep are the layer of the earth?

Plate Tectonics

German scientist Alfred Wegener was the first who found that the coastal length of Africa and South America seemed like a jigsaw puzzle that fit together. He also got proof of the same by studying and analyzing the plant and animal fossils along the coasts of these continents, even though now they were separated by vast oceans.   He also noticed that physical formations, like mountain ranges, on the two continents also were same.

Later in the book, The Origin of Continents and Oceans, he described that the earth’s continents were once one large mass and called it the supercontinent Pangaea, meaning “all the earth”. Pangaea is believed to have split into different landmasses and continental pieces in geological time and now moved to its current locations on the planet.

Continents drifting

Around 200 million years ago

Pangaea breaks up into two major land masses. Laurasia in the north made up of North America and Eurasia andGondwana in the south.

 Around 135 million years ago

Gondwana separates even more. South America and Africa drift from the Australian antarctican landmass

Some 65 million years ago

Laurasia separates from Eurasia and North America and then Africa is separated from South America and Madagascar as South America drifts away.

50-40 million years ago

Now Greenland moves away from North America and Australia floats northwards separating from Antarctica.

The modern plate tectonics theory, says that the earth’s outer layer, or lithosphere, is broken into several large pieces called plates.

These are tectonic plates, which hold the continents and oceans and are slowly but constantly moving on the Earth’s surface. The movement of the plates proves that the continents are not fixed and had moved over time, and also describes how and why earthquakes, volcanoes, and other events occur in Nature.

Check Point

I.  Explain the following:

  1. Crust
  2. Mantle
  3. Outer core
  4. Asthenosphere
  5. Lithosphere
Answer Key
  1. Crust: Crust is the top or the outermost layer. It is very solid, and also the thinnest of all layers, only about 5000m thick under the oceans and about 30000m of thickness under the landmasses.
  2. Mantle: It is made of two parts, upper and lower, the thick layer is made of extremely hot, semisolid rock is located directly below the crust and is about 1,800 miles (2,900 km) thick.
  3. Outer core: The outer core is the only layer which is a liquid layer: an ocean of mostly thoroughly liquid iron and nickel. It is about 1,800 to 3,000 miles below the surface and about 2,300 km thick.
  4. Asthenosphere: The upper mantle makes the plates of the lithosphere move on this hot, liquid magma right below the lithosphere
  5. Lithosphere: This layer is made up of the crust and a very small lining of the upper mantle; it is split into many slowly moving plates of solid structure that consists of the continents and oceans.

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