How do you measure something you can’t observe directly? Earth’s Interior How do you measure something you can’t observe directly?

300 years ago, Isaac Newton used observations of the planets and his law of gravity to calculate that the density of the Earth was double that of the surface rocks. His density value is essentially unchanged today. Great hair. Greater scientist. Newton

Therefore, since 1700 we have known that the interior of the Earth was composed of different material to the crust. We now differentiate the interior into two types of mantle (asthenosphere and lower mantle) and two types of core (outer and inner). The key to measuring the size of each of these regions is the study of seismic waves. Differentiation

Two ways to divide into layers By chemical composition (what it’s made of): Crust Mantle Core By physical properties (density, state of matter, etc.): Continental crust Oceanic crust Asthenosphere (plastic part of upper mantle) Lower mantle Outer Core Inner Core Two ways to divide into layers

Waves change speed when they pass from one medium to another. Why Waves change speed when they pass from one medium to another. Why? Well, look at this lawnmower: Refraction

Longitudinal / Compression Transverse P-waves S-waves Faster Slower Longitudinal / Compression Transverse Pass through all states of matter Only pass through solids Go to YouTube and search for “Curving Seismic Paths”

Seismic waves refract when they pass through the mantle/outer core boundary. No P-waves can be detected between 104 and 140 degrees from the focus of an earthquake.

Why can’t we detect any P-waves in the shadow zone? Why can we detect P-waves opposite the earthquake focus?

S-waves aren’t completely blocked by the outer core, they are attenuated. This means they gradually fade to nothing. Another example: sunlight is attenuated by sunglasses. So only P-waves are detected on the opposite side of the Earth. Attenuation