Scientists can infer the interior composition of the earth by

Scientists discovered the internal structure of the earth by using seismic waves. The most common seismic waves are S waves and P waves. While S waves have more energy, they can only move through solids. Also, they are quite slow compared to other waves.

On the other hand, P waves are faster and have less energy, but they can move through all three states of matter. Since we have earthquake detectors, we use the detectors to figure out if there is a difference in speed.

Almost all planetary landing missions now in the design stage include seismological instrumentation and some even include sample return. Hopefully the best science is yet to come. But even on Earth, where thousands of seismometers have been deployed and new experiments, such as the National Science Foundation's EarthScope, are now being conducted, each new observation raises as many questions as it answers.

Earth's story has been written, but we're only on the first few chapters. Answer originally published August 23, Sign up for our email newsletter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. Cutaway view showing Earth's interior structure. Source USGS. Do you ever wonder what's below your feet?

Not just a few yards or meters below, but way down deep - many miles or kilometers below the surface? Have you wondered how scientists know the basic structure of Earth's interior or how the interior structure relates to plate tectonic boundaries? More information about the Earth's composition comes from studying meteorites, which provide information about the likely origin of our solar system. It is impossible to drill to the center of the earth, so scientists rely on indirect observations of matter lying below the surface through use of seismic waves and their knowledge of how these waves travel during and after an earthquake.

The speed of seismic waves is affected by the properties of the material the waves pass through; the stiffness of material affects the speed of these waves. Measuring the time it takes for certain waves to get to a seismometer after an earthquake can indicate specific properties of the materials that the waves encountered.

There are two types of seismic waves: P-waves, or pressure waves, which go through both liquids and solids, and S-waves, or shear waves which go through solids but not liquids. P waves are the faster of the two, and the gap between them provides an estimate of the distance to the earthquake.

Seismic studies from indicate that the outer core is liquid and the inner core is solid. A permanent magnet could not exist at the high temperatures found at the center of the Earth, so scientists have concluded that the core is liquid. Earth also possesses a gravitational field.