1. The Formation and Structure of Planet Earth Lesson #2: The Maturing Earth Lesson Objective #2

2. Objective #2 (Chapter 1, CRO #5) Identify and describe the 5 layers of Earth as arranged by their physical properties and structure. –Refers to their physical consistency such as: Solid and rigid (non flexible) Solid and plastic (flexible, gooey, able to flow like warm wax or gelatin) Liquid

3. The Lithosphere The outermost rigid shell of earth that includes all of the crust but also a portion of the upper mantle as well. Rocks are solid and rigid. The rocks in the mantle portion as much more dense that the crustal portion due to a different composition.

4. The Aesthenosphere About 200 km beneath the surface, the temperatures approach the melting point of the mantle rock, but do not exceed it (in most places). Here the rock is in a “plastic” state of a soft, gooey solid that is able to flow. This region is called the aesthenosphere. It is indicated with a solid black line on the next figure.

6. The Mesosphere Beneath the aesthenosphere, the temperatures do not rise as quickly as pressure, which acts to keep the rocks solid. Here, the rocks are strong and rigid once again. This region of the mantle (lower) is called the mesosphere. Meso means “middle”.

8. The Outer Core Notice on the previous slide the sudden and dramatic drop in melting point of the material at a depth of about 3,000 km. This drop is due to a change in composition from rock to pure metals. The drop is so great that the metals here are in liquid form. This region is known as the “outer core”.

9. The Inner Core As the pressures continue to increase deeper down, the melting point of the metals in the core rises above the temperature. The result is an inner core of solid metal (mostly iron and nickel).

10. The continents have a higher elevation than the ocean floor because they are thicker and float higher in the mantle due to their lower density.