The Earth’s Structure

Planet AppleGeology is the study of what’s on and in the Earth. We can see what’s on the earth, but what’s inside? Cut into an apple to get an idea of the Earth’s insides.

1. Cut an apple in half vertically. Cut the apple in half again, this time horizontally.

2. Examine the apple. Apples and the Earth have a lot in common. They are both round and solid. They are both surrounded by a very thin skin or crust; look how thin the apple’s skin is relative to the whole apple. Both an apple and the Earth have a core. And they both have a thick layer between the skin or crust and the core.

3. Look closely at the apple’s core. You should see the seeds surrounded by a hollow space which is surrounded by a harder shell. This is something like the earth’s inner and outer core; the Earth’s inner core is solid and its outer core is thick liquid.

The Earth’s InteriorEver wondered what our earth is made of?  Think of it as an apple.  An apple constitutes the skin, the pulp and the core in the middle.  Similarly, the earth is made up of the thin outermost layer called the crust, the innermost part called the core, and the part in between them called the mantle.

(Fig 1.1) The apple and the structure of the Earth

At the beginning, the early earth seemed to have heated up, the centre became molten, and convection currents developed as the lighter compounds tended to rise towards the surface forming the brittle crust.  Together with the top part of the mantle, it formed the hard slabs known as lithosphere.  The continents are embedded in these slabs.  The lithosphere is divided into oceanic and continental crusts. Oceanic crust (sima), the floor of the deep oceans, is thin, about 7km thick, and made of relatively dense rocks like basalt.  Continental crust (sial) is much thicker, averaging 33km, and is composed of relatively light material such as granite.

(Fig 1.2) The Crust (Oceanic and Continental).

The denser materials such as iron sank to form the core.  It is partly solid. 

Temperatures are extremely high, at about 3000oC.

(Fig 1.3) The Core.

Between the core and the crust, the intermediate zones form the mantle, which is mainly solid rocks but there is also a layer of molten rock called magma nearer the core. Temperatures are high, at about 2000oC.

Fig 1.4) The Mantle.

The Earth’s Structure THE CORETHE CORE

The inner part of the earth is the core. This part of the earth is about 2,900 km below the earth's surface. The core is a dense ball of the elements iron and nickel. It is divided into two layers, the inner core and the outer core. The inner core - the centre of earth - is solid and about 1,250 km thick. The outer core is so hot that the metal is always molten, but the inner core pressures are so great that it cannot melt, even though temperatures there reach 3700ºC. The outer core is about 2,200 km thick.

The Earth’s Structure THE MANTLETHE MANTLE

The layer above the core is the mantle. It begins about 10 km below the oceanic crust and about 30 km below the continental crust (see The Crust). The mantle is to divide into the inner mantle and the outer mantle. It is about 2,900 km thick and makes up nearly 80 percent of the Earth's total volume.

The Earth’s Structure THE CRUSTTHE CRUST

The crust covers the mantle and is the earth's hard outer shell, the surface on which we are living. Compared to the other layers the crust is much thinner. It floats upon the softer, denser mantle. The crust is made up of solid material but this material is not the same everywhere. There is an Oceanic crust and a Continental crust. The first one is about 6-11 km thick and mainly consists of heavy rocks, like basalt. The Continental crust is thicker than the Oceanic crust, about 30 km thick. It is mainly made up of light material like granite.

Earth’s Structure NotesEarth’s Structure Notes

Part of the Part of the EarthEarth

ThicknessThickness StateState

Crust 6km under the oceans;

Average 30-40km;

Up to 70km under continents

Solid, rigid

Mantle Upper 100km

Total about 3000km

Rigid

Plastic – will flow very slowly

Outer Core

Inner Core

About 2300km

About 1200km

Liquid

solid

Continental DriftContinental DriftHumans have divided the land surface of the earth into large pieces called continents. Nature has done this too. In the natural world, these continents actually move, albeit only millimetres each year. To learn more about drifting continents, complete the activity below.

1. Observe the animation loop that appears on your computer screen. In a couple of sentences, describe what your see.

Each of the following statements about continental drift are false. Rewrite them to make them correct.

a. Fifty millions years ago, all the land was one continent.

b. The name of the continent was Africa.

c. The crust of the earth is one large piece.

d. The continents are moving at a very fast pace.

e. The continents will stop moving shortly.

f. In the future the earth will look much as it looks today.

Complete the table below to record some of the characteristics of the layers of the earth

Internet Sites

1. Plate Tectonics

2. Evidence Supporting Continental Drift