Let’s explore some facts about the layers of the earth! Then, why not take a look at our question sheet in the activity section at the end to test what you have learned.
The Earth is made of three layers that are just like an onion – the crust, the mantle and the core. Some of these layers have even more layers in them and are always moving.
The Earth is mostly made of rock and metal. As scientists can’t really get right to the middle of the earth, it’s not easy for them to know what’s way down in the middle. There are always new theories coming out as measuring equipment and knowledge improves.
The core is made of two layers – the inner and outer core. When the Earth formed 4.5 billion years ago, the heavy substances sunk to the middle and these formed the inner core. The lighter ones are like air and water stayed on the top on the crust.
The innermost part of the core is a bit like a solid lead ball, which is about 1,500 miles (2,400 kilometers) thick. That is thick! Under all that pressure, it actually can’t melt. Are you ready for this? It is between 9,000 and 13,000 degrees Fahrenheit (4,982 and 7,204 degrees Celsius) in temperature.
That is seriously hot and unbelievably it’s as hot as the sun’s surface. When you think that a kettle reaches 212 degrees Fahrenheit (100 degrees Celsius) at boiling point, then you can imagine just how hot the inside of the Earth is.
The inner core is said to spin at a different speed to the rest of the planet causing the Earth’s magnetic field.
The second layer of the core is made of liquid iron and nickel and is about 1,400 miles (2,300 kilometers) thick. Some people have said that it is actually 3,200 miles (5,150km) thick and 7,200 to 9,000 degrees Fahrenheit (3,982 to 4,982 degrees Celsius) in temperature. It is because of the flow of metals in this inner core that the Earth is magnetic. The influence of this magnetic field extends beyond the Earth far into space and forms a barrier that helps protect the Earth from the Sun’s destructive solar winds. Wow that’s interesting.
The mantle is about 1,800 miles (2,900 kilometers) thick and makes up about 85% of the Earth’s weight.
It is made of molten (melted) iron, minerals and other semi-solid rocks that can flow under pressure. It is thought that when the rocks rise due to the very intense heat and then cool, this means that they sink back to the core and this movement causes the crust to break into sections, or plates. When these move and crash into each other it causes earthquakes and volcanic eruptions. It is because of this movement that mountains and new sea floors are formed.
Sea floors are made of a thick rock called basalt which press into the mantle and can then fill with water. The various continents are made from lighter blocks that float on the mantle like massive icebergs.
When the mantle layer is explored they usually do it from the sea bed where the layer is thinner than on land. The first time they explored the mantle was in 1996, but they eventually gave up as they just couldn’t get it right. In 2007 scientists drilled to 23,000 feet (7,000 m) below the seabed from a Japanese ship called Chikyu, in an area between Cape Verde Islands and the Caribbean Sea. This drilling was three times deeper than any other previous drillings that they had done.
The crust is an outer solid layer and is where life as we know it exists with mountains, sea and soil. It is about 3-5 miles (5 – 8 kilometers) thick in the ocean bed. It is mostly made from basalt rock and is around 25 miles (40 kilometers) thick on land which is mostly made from granite rock. This is the only layer of earth that can be investigated by drilling into it. So we know way more about his layer than any of the others!
The layers beneath the crust are investigated by watching how the waves that travel through the Earth (Seismic waves) from earthquakes or eruptions, behave. The machine that is used to measure these waves is called a seismograph.
Test your knowledge of this subject using our activity sheet to use in class or at home: Questions about Layers of the Earth (all answers found on this page).