1. Earth’s Structure
Section 22.1

2. Science of Geology
Geology- Study of planet Earth, including its composition and structure.
Scientists who study Earth and processes that have shaped Earth over time are called geologists.

3. Science of Geology (Cont.)
Modern science of geology began in 1700’s with James Hutton.
Hutton was a Scottish physician and farmer who made observations of rocks and explained Earth was far older than most people had imagined.
Also observed that some rocks came from particles from older rocks, thus realizing that Earth changed gradually over time.

4. Science of Geology (cont.)
Hutton developed the principle of uniformitarianism, an idea that the geologic processes that operate today also operated in the past.
Dramatic features such as mountains and canyons are the result of geologic process that work very slowly over long periods of time.

5. A Cross Section of Earth
Earth’s surface and interior can be compared to a hard-boiled egg.
Earth is divided into 3 main layers:
Crust
Mantle
Core
Layers are divided based on material of each layer.

6. The Crust Rocky outer layer of the Earth is the crust
Thinner compared to other layers
Most of crust is made of silicates, rocks made of compounds of silicon and oxygen. Often contain metals such as aluminum, iron, or calcium.

7. The Crust (cont.)
2 different types of crust: continental crust and oceanic crust.
Continental- Rock that makes up continents, consists mainly of less-dense rocks such as granite.
Averages 40 km in thickness, although ranges about 8 to 75 km

8. The Crust (cont.)
Oceanic Crust- composed of mostly dense rocks like basalt.
Oceanic Crust is about 7 km thick on average, and it much thinner than continental crust

9. The Mantle
Beneath the crust is the mantle, a thick layer of hot but solid rock.
Mantle extends about 2850 km from beneath the crust to the top of the core.
Pressure and temperature increase tremendously the deeper you go into the mantle.
Mantle is composed mainly of silicates, and is rich in iron and magnesium.

10. The Mantle (cont.)
Geologists divide mantle into 3 layers based on physical properties of rock:
Lithosphere
Asthenosphere
Mesosphere
Lithosphere- Layer of relatively cool, rigid rock that includes the uppermost part of the mantle as well as the Earth’s crust.
Lithosphere measures about 100 km, although it is thicker below the continents and thinner beneath the oceans.

11. The Mantle (cont.)
Asthenosphere- Layer of softer, weaker rock that can flow slowly
Mesosphere- Lower part of the mantle; stiffer rock of mesosphere extends all the way down to the upper surface of Earth’s core.

12. The Core
Beneath mantle is the core; a large sphere of metal that occupies Earth’s center.
Scientists think that core is composed mostly of iron, with lesser amounts of nickel and some lighter elements.
Within the core, pressure increases greatly with depth.

13. The Core (cont.)
At Earth’s center, pressure is estimated to be 3.6 million times the pressure of Earth’s surface!
Temperature at center of Earth is estimated to be about degrees Celsius (nearly temp. of sun’s surface)
Core is divided into 2 parts:
Outer Core
Inner Core

14. The Core (cont.) Outer Core- High temperatures keep the meta liquid.
Because of Earth’s rotation, flowing iron of the outer core produces an electric current and creates Earth’s magnetic field.
Inner Core- Very high pressure is a more important factor than temperature. Inner core is solid.