Identify the best explanation for the important role of the liquid outer core, and not the solid mantle, in forming Earth’s magnetic field. A The mantle moves very slowly compared to the outer core. B The outer core moves more quickly than the mantle and has a higher metal content. C The outer core is mostly iron and nickel and the mantle is mostly silicon and oxygen. D The outer core is closer to the center of the planet than the mantle. Identify the best explanation for the important role of the liquid outer core, and not the solid mantle, in forming Earth’s magnetic field.

One ingenious way scientists learn about Earth’s interior is by looking at how energy travels from the point of an earthquake, called seismic waves. Seismic waves travel outward in all directions from where the ground breaks at an earthquake. Seismograph stations measure the energy released by these earthquakes, but there are two that scientists are most interested with in regards to understanding the interior of the earth.Primary waves (also called P-waves) are fastest, traveling at about 6 to 7 kilometers (about 4 miles) per second, so they arrive first at the seismometer. P-waves move in a compression/expansion type motion, squeezing and unsqueezing earth materials as they travel. P-waves bend slightly when they travel from one layer into another. Seismic waves move faster through denser or more rigid material. As P-waves encounter the liquid outer core, which is less rigid than the mantle, they slow down. This makes the P-waves arrive later and further away than would be expected. The result is a P-wave shadow zone. No P-waves are picked up at seismographs 104o to 140o from the earthquakes focus.

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