1. The Earth
Chapter 2, Section 1

2. The Earth Third planet from the sun. Age: 4.6 billion years
Shape: Oblate spheroid (slightly squashed sphere)
Size: 12,756 km diameter.
Mass: 6 x 1024 kg

3. Earth is Unique
Liquid water
Atmosphere with oxygen
Life

4. What’s Inside? How can we tell? Shovel? Really big drill?
Shine a light?
Send sound waves?
Really BIG sound waves?
Wait for an earthquake, see where seismic waves go?

5. Indirect Methods
We use seismic waves, and studies of gravity, density and magnetism to identify what’s inside the Earth.
There are two kinds of seismic waves: S waves & P waves.
S waves do not go through liquids.

6. Using Seismic Waves
We can tell the states of the interior layers because of how seismic waves travel through them.
To do this, we need worldwide cooperation of scientists.

7. Main Layers
The main layers of the Earth are the Crust, the Mantle, and the Core.
The crust is the hard outer shell, which is very thin.
The mantle is the middle layer, made of several elements.
The core is mostly iron & possibly nickel, as metals.

8. Two Ways to Look at Earth

9. Two Ways to Divide the Earth
We can look for layers of the Earth with different elements, or by state of matter.
States of matter give us five layers, instead of three from composition.
The outer layers overlap between the two methods.

10. Structural Layers
The lithosphere includes the crust and solid outer mantle.
A mobile, plastic layer under the crust is the asthenosphere.
More solid mantle is the mesosphere.
The outer part of the core is liquid.
The inner core is solid.

13. Trends As we move towards the center of the Earth, Temperature rises
Density increases
Pressure rises

14. Density Density is how much matter there is inside a space.
Density = mass / volume.
Density is how much matter there is inside a space.
Density is very important to Earth Science.

15. The Earth is a large magnet, surrounded by a magnetic field.

16. Magnetic Field Protects

17. Compasses use the Earth’s magnetic field.

18. Earth has gravity. Gravity holds the planet together.
Gravity pulls denser matter to the inside.
Gravity weakens as the attracted object is moved further from the center of the Earth.

19. Smaller moons and planets have weaker gravity.
Astronauts weigh less on the moon than on Earth.

20. Mass and Weight
Weight is the force of gravity on an object, measured in Newtons or pounds.
Mass is the amount of matter present. It does not change with lower gravity.