Now we will explore the five structural zones. The Earth's structural zones, also called the S-Zones, are as follows: 1.the lithosphere 2.asthenosphere 3.mesosphere 4.inner core and 5.the outer core. Over the years, scientists have measured seismic waves from earthquakes. These waves have helped scientists to learn more about the inside of our planet. The lithosphere is part of the crust and the upper mantle. The prefix "lithos" is Greek for "stone" or "rock." This layer is solid and the most rigid of the other layers. It is about 15 to 300 kilometers thick. The asthenosphere lies below the lithosphere. This layer is about 200 kilometers thick and contains hotter, softer rock that flows like lava. Its prefix "asthenes" is Greek for the word "weak." Keep in mind; it is not as weak as a brittle piece of wood. However, it is weaker than the other layers. The mesosphere or "middle layer" is found at the lower part of the mantle. Scientists believe it is solid rock. If you travel farther into the center of the Earth, you will come to the inner and outer cores. The outer core, which is about 2,300 kilometers thick, is located about 2,900 kilometers below the surface. However, because the scientists have not seen this area, it is believed that the outer core is made of a dense liquid. The inner core is a solid ball that is about 2,400 kilometers in diameter. Scientists believe the inner core is made of solid, dense nickel and iron. The inner and outer cores constitute about 1/3 of the Earth's mass.
