1. Chapter 2: Earth as a System
2.1 Earth: A Unique Planet
Chapter 2: Earth as a System
Austin High School
Earth and Space

2. Earth is Unique for Several Reasons
Only know planet that has water on it surface
Atmosphere contains large proportion of oxygen
Know to support life

3. Earth Basics 3rd planet from the sun Formed 4.6 billion years ago
Made mostly of rock
70% surface covered by the thin layer of water called global ocean
Earth is oblate spheroid- slightly flattened sphere
Spinning of earth on its axis makes the polar region flatten and the equatorial zone bulge.
Earth pole to pole circumference- 40,007 km
Earth equatorial circumference- 40,074 km

4. Earth Basics Earth surface relatively smooth
Distance between high points and low points are small relative to earth’s size
Height of tallest mountain and the depth of deepest ocean trench is about 20 km
Small compares to earth’s average diameter of 12, 756 km.

5. Earth’s Interior
Direct observation of earth’s interior is limited to upper few kilometers reached by drilling
We rely on indirect methods to study earth’s greater depths
Ex. Through studies of seismic waves, and the way they travel through the earth, we have learned it is made up of:
3 major compositional zones (crust/mantle/core)
5 major structural zones (lithosphere/asthenosphere/mesosphere/outer-core/inner-core)

6. Composition Zones of Earth’s Interior Crust
The thin, outermost zone of earth’s is called the crust
Crust makes up 1% of earth’s mass
Crust beneath the oceans is called oceanic crust (5-10 km thick)
Crust that makes up the continents is called continental crust (15-70 km thick)
Continental crust is thickest beneath high mountain ranges.
The crust of the Earth is broken into many pieces called plates.

7. Composition Zones of Earth’s Interior Mantle
The mantle, layer that underlies the crust
Mantle is denser than the crust, its nearly 2,900 km thick and makes up 2/3 of the earth’s mass.

8. Composition Zones of Earth’s Interior Core
Center of earth is a sphere, radius is about 3,500 km, called the core
Mainly composed iron and nickel

9. The 3 compositional zones of earth’s interior are divided into five structural zones.

10. Structural Zones of Earth’s Interior Lithosphere
Lithosphere is the solid, outer layer of earth that consists of the crust and the rigid upper part of the mantle
Uppermost part of the mantle is cool and brittle
Rigid layer is 15 to 300 km thick

11. The Lithospheric Plates
The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, semi-rigid asthenosphere.

12. Structural Zones of Earth’s Interior asthenosphere
The solid, plastic layer of the mental beneath the lithosphere
Made of mantle rock that flows very slowly
Allows tectonic plates to move on top of it
200 km thick

13. Convection Currents
The middle mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again --repeating this cycle over and over.

14. Structural Zones of Earth’s Interior mesosphere
Literally the “middle sphere” the strong lower part of the mantle between asthenosphere and outer core
Pressure is so large that it is solid, its rigid
The lower mantle, ends at 2900 km deep

15. Structural Zones of Earth’s Interior Outer Core
At the depth of about 2900 km lies the boundary between mantle and the outer core
Outer core is a dense liquid
The core of the Earth is like a ball of very hot metals.
The outer core is made up of iron and is very dense.

16. Structural Zones of Earth’s Interior Inner Core
Inner core begins at a depth of 5150 km
Inner core is dense, rigid solid
The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move.

17. Earths Interior Part 2
To learn about Earth's interior, scientists use energy to “see” the different layers of the Earth, just like doctors can use an MRI, CT scan, or x-ray to see inside our bodies.

18. by looking at how energy travels from the point of an earthquake
by looking at how energy travels from the point of an earthquake. These are seismic waves (Figurebelow). Seismic waves travel outward in all directions from where the ground breaks at an earthquake.
Two types of seismic waves are most useful for learning about Earth’s interior.

19. P waves
P-waves (primary waves) are fastest, traveling at about 6 to 7 kilometers (about 4 miles) per second, so they arrive first at the seismometer.
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.

20. S waves
S-waves (secondary waves) are about half as fast as P-waves, traveling at about 3.5 km (2 miles) per second, and arrive second at seismographs. S-waves move in an up and down motion perpendicular to the direction of wave travel.
This produces a change in shape for the earth materials they move through. Only solids resist a change in shape, so S-waves are only able to propagate through solids. S-waves cannot travel through liquid.

21. By tracking seismic waves, scientists have learned what makes up the planet’s interior
P-waves slow down at the mantle core boundary, so we know the outer core is less rigid than the mantle.
S-waves disappear at the mantle core boundary, so the outer core is liquid.