Earth’s Interior 6C

Indirect Evidence We have never seen deep inside the Earth. Geologists use an indirect method that relies on inferring what might be below the surface. Using data from seismic waves, astronomy, and other sources, scientists have learned the Earth is made of layers.

Temperature A measure of how fast the particles of a substance are moving. At first, the Earth gets a little cooler as you go deeper. But at 20 meters depth, the temperature starts rising. For every 40 meters you descend, the temperature rises about 1° Celsius. After a few kilometers this rate slows a bit, but it gets hotter the deeper you travel inside the Earth.

Pressure Is the force pushing on a certain area. The deeper you go, the more rocks are above you. The more rocks there are, the more they weigh. So the deeper you go, the greater the pressure pushing on you.

The Earth’s Layers

Why Does the Earth have Layers? When the Earth formed, it was molten rock. As the Earth cooled, the denser materials (Fe and Ni) sank to the core. The earth’s rotation flung the lighter elements towards the surface. So the earth layers are caused by density. This process is called differentiation.

Crust Forms the Earth’s outer skin. Very thin layer. If the Earth were an onion, this layer would be like the paper thin skin of the onion. Oceanic crust: thinnest, made of dense basalt. Continental crust is thickest, made of less dense granite.

The Mantle Layer below the crust Solid Very hot rock Pressure and temperature increase as we go deeper. Upper mantle is divided into two parts, the lithosphere and the asthenosphere.

Lithosphere Lithosphere is the upper part of the mantle and the crust. Litho means stone in Greek. The crust and upper part of the mantle are very similar, so they are combined in this layer. The lithosphere actually floats on top of the soft rock below it.

Asthenosphere Upper mantle, right below the lithosphere In Greek, asthenes means “weak.” Less rigid than the layers above. Rock is hot and soft, like road tar on a hot summer day. This material actually flows slowly.

The Core Has two parts: Liquid outer core Solid inner core Both made of nickel (Ni) and iron (Fe) Outer is a liquid molten metal Inner core is a solid metal Liquid outer core causes the Earth to have a magnetic field

Earth’s Magnetic Field Spinning outer core produces a magnetic field Causes planet to be like a large bar magnet Compasses will point to the Earth’s magnetic pole, not the geographic pole This magnetic field helps protect the Earth from harmful radiation from space