LR257.2.4: Density and Earth's Layers

Mass is a measure of the amount of stuff in an object. These two forks are the same size, one is made of metal and one is made of plastic. Which fork has more mass?

Volume is the amount of space that matter takes up. The more space an object takes up, the more volume it has. For example, the cake takes up more space than the cupcake, so the cake has more volume than the cupcake.

Check for Understanding:

Liquids have a definite volume, but have no definite shape because they take the shape of the container they are in.

1. A graduated cylinder is used to determine the volume of a liquid.

2. The volume of the liquid in this graduated cylinder is 150 mL.

Density is a measure of how much matter there is in a certain amount of space.

For example, a balloon is much less dense than a pear:

To find the density of an object, first find the mass and the volume of the object. Then, divide the mass of the object by the volume of the object.

For example, a super ball has a mass of 45 g and a volume of 45 mm3. To find the density of the super ball, divide the mass by the volume:

density = 45 g ÷ 45 mm3

The density of the super ball is 1 g/mm3

If you pour two liquids with different densities together, they will form layers. The liquid with the highest density will be on the bottom, and the liquid with the lowest density will be on the top. This is called a float test.

For example, in this picture

•The red liquid has the lowest density.

•The green liquid has the highest density.

•The yellow liquid's density is in between the red and green's.

When using a float test to determine density, a solid object placed in the layers of liquid will float above the liquids with a higher density and below the liquids with a lower density.

It is easy to see the landforms, oceans, and creatures on Earth's surface, but its internal structure is hidden below. The Earth is not all one consistent material inside. Instead, it is made up of layers. The Earth's layers are the crust, the mantle, the outer core, and the inner core. Each of the layers of the Earth is unique in terms of its composition, temperature, and thickness.

This cross-section of the planet reveals Earth's layers. The onion has an outer peel and inner layers. Similarly, the Earth has an outer surface and inner layers.

The mantle is very thick. As a result, the top of the mantle has different properties than the bottom of the mantle. The top of the mantle is solid, hot rock. Further down in the mantle, the high pressure and high temperatures mean that the rock can flow, which creates magma. The mantle ranges in temperature from 360°C to 2,500°C.

The lithosphere is the rigid outer section of the Earth that is made up of the crust and the upper mantle. The lithosphere is the hard and rigid outer layer of Earth, which is why the lower mantle is not included.

The material in the mantle does not stay still. Instead, convection currents in the mantle cause cooler rock to flow down and hotter rock to flow up. This movement continues constantly.

The mantle is always in motion thanks to convection currents. The hot, less dense liquid rock (or magma) rises, and the cool, more dense magma sinks.

Many travelers use compasses to navigate. A compass's needle points north, which can help travelers figure out which way to go. Compasses work because of the Earth's magnetic field.

This compass's needle is pointing north.

The Earth's magnetic field helps protect the planet from solar wind, or strong currents of particles that are released from the Sun's surface. Without the magnetic field, it would be difficult to live on Earth. Activity in the Earth's outer core helps to create the magnetic field. Like the mantle, the outer core has convection currents that move the matter that makes up the layer. These currents and the specific material that the outer core is made of cause the magnetic field.

This diagram shows how convection currents in the outer core produce the Earth's magnetic field.

The Earth's outer core has temperatures of up to 5700°C, and the inner core has temperatures of up to 5400°C. With temperatures that high, one would expect both the outer and inner core to be hot liquid. However, gravity acts on all of the Earth's matter and creates so much pressure on the inner core that it remains in a solid state.

Gravitational force, represented by the red arrows, causes the inner core to remain solid.

The inner layers of the Earth are too deep, too hot, and are under too much pressure for scientists to physically travel to them. However, researchers are still able to learn about the layers of the Earth in other ways.

In some places on the ocean floor, there are cracks in the oceanic crust, and material from the mantle is pushed up onto the ocean floor. Once the mantle material spreads onto the surface of the sea floor, it cools, and scientists are able to study its composition and learn more about the mantle.

This image shows a crack in the oceanic crust that is allowing hot material from the mantle to spill out onto the ocean floor.

Scientists can also learn about the layers of the Earth by studying the vibrations, or seismic waves, produced by earthquakes. These waves travel through the layers of the Earth. Vibrations travel at different speeds through different substances.

This diagram shows how seismic waves travel at different speeds through the different layers of Earth. The waves travel out in many different directions from the focus of the earthquake, also known as its epicenter.

By studying how waves from vibrations move through the different layers and materials of the Earth, scientists can learn about those layers and materials. The waves are bent, sped up, or slowed down when they pass through the Earth's layers. The type of material affects the speed of the waves, and they can change direction when they reach a new layer. Scientists study the path and speed of these waves to identify where layers begin and end and what materials make them up. For example, scientists believe that the Earth's core is mostly iron. After they make these guesses, they can perform tests on those materials to see how they respond to extreme heat and pressure.