1. The Composition and Layers of the Physical Earth
Planet Earth
The Composition and Layers of the Physical Earth

2. Chapter Objectives The Earth as a system How large is the Earth?
What is Earth’s shape? Evidences..?
The spheres of the Earth and their compositions.
Atmosphere
Hydrosphere
Geosphere

3. Earth as a System
Earth is a dynamic body with many separate but highly interacting parts – or spheres.
Earth as a system –
Nearly endless array of subsystems.
e.g. – hydrologic cycle, carbon cycle
Sources of Energy
Sun – Drives external processes
Weather and climate, Ocean circulation, & Erosional processes
Earth’s Interior – nuclear, chemical, & thermal energy drives internal processes
Volcanoes, Earthquakes, & Mountain building
Humans are part of the Earth system

4. Earth’s Size
Earth’s Circumference – distance around the earth was first measured by Eratosthenes 2000 years ago.
Measured the distance between Egyptian cities of Alexandria and Syrene.
Measured the sun’s angle at noon at each location.
Difference in angle is a fraction of a circle.
Multiple distance by fraction to get circumference.
Obtained 46,250 km – very close to the real 40,000 km circumference

5. Eratosthenes’ Method

6. Earth’s Numbers Equatorial Polar Diameter Circumference 12,174 km

7. The Earth’s Shape The shape of the Earth is usually thought of as a
Spheroid
Oblate
Sphere
The Earth’s Shape
The shape of the Earth is usually thought of as a
From observations & measurements by earth scientists we know that the Earth is slightly flattened at the poles, and slightly budging at the equator. Thus, the shape is called a(n)

8. Earth looks spherical from space
Earth’s Shape
Because the Earth spinning on its axis –
It bulges at the equator
It flattens at the poles
Earth looks spherical from space

9. Evidence of Nearly Spherical Shape
As we now know that the Earth is NOT flat (as it was once believed). Columbus, Magellan
The position of the sun and the stars depends on the position on Earth, thus the earth has to be curved.
On of the best known stars in the North Star –
The angle of Polaris in the sky increases as one travels towards the North Pole, where it is directly overhead (90⁰)
POLARIS
42⁰
At North Pole
At ALCS

10. Evidence Cont.… Ship masts appear 1st on the horizon.
Earth’s shadow is curved when seen during a lunar eclipse.
*Astronauts have photographed Earth from space*

11. Star Trails (Time Lapse Photography)
Evidence for Earth’s Rotation on its axis

12. Spheres of the Earth
Geosphere: Consists of all the rock and fluid inner layers of the Earth

14. Spheres of the Earth
Geosphere: Consists of all the rock and fluid inner layers of the Earth
Hydrosphere: Consists of all the water on Earth’s surface; oceans, rivers, lakes, streams, etc. Covers ~71% of surface.

16. Spheres of the Earth
Geosphere: Consists of all the rock and fluid inner layers of the Earth
Hydrosphere: Consists of all the water on Earth’s surface; oceans, rivers, lakes, streams, etc. Covers ~71% of surface.
Atmosphere: Consists of the “shell” of gases that surrounds the earth

18. Average Chemical Compositions
ESRT – Front Cover

19. Percent Composition of the Atmosphere
Our atmosphere is mostly Nitrogen (78%), followed by Oxygen (21%). CO2 makes up less than 1%.

20. Properties of the Atmosphere
ESRT – Page 14

21. Ozone Depletion The ozone absorbs harmful UV rays from the Sun.
Depletion caused by CFC’s (ChloroFluoroCarbons) found in aerosols, Styrofoam, and refrigerants.
Problem from ozone depletion is increased skin cancer in humans.

22. Atmospheric Phenomena
Aurora Borealis in Ionosphere

23. Hydrosphere All the water on the Earth covers ~71% of the surface
Freshwater (2%) – Rivers, Lakes, Streams, & Marshland
Marine (97%) – Saltwater Oceans
Ice (1%) – Continental and Mountain/Alpine Glaciers

24. Structure of Earth’s Geosphere
Page 28 in Text ….

25. Compositional Zones Crust – The thin outer most zone
Continental & Oceanic crust make up 1% of the Earth’s Mass.
The Lower boundary is the MOHO – or Mohorovicic Discontinuity
MOHO

26. Compositional Zones Crust – The thin outer most zone
Continental & Oceanic crust make up 1% of the Earth’s Mass.
The Lower boundary is the MOHO – or Mohorovicic Discontinuity
Mantle – Below the crust
Denser than crust
66% of Earth’s mass
Silly-putty like

29. Compositional Zones Crust – The thin outer most zone
Continental & Oceanic crust make up 1% of the Earth’s Mass.
The Lower boundary is the MOHO – or Mohorovicic Discontinuity
Mantle – Below the crust
Denser than crust
66% of Earth’s mass
Silly-putty like
Core – Composed mainly of Iron and Nickel.
Outer core is a dense liquid
Inner core is a dense solid
33% of Earth’s mass

32. Structural Zone
Three compositional zones are divided into five structural zones:
Lithosphere – Crust and cool brittle upper mantle. 15 – 300 km thick
Asthenosphere – Less ridged layer with more ability to flow due to enormous amount of heat and pressure (plasticity). 200 – 250 km thick
Stiffer Mantle – Layer od solid mantle rock
Outer Core – Dense liquid, mostly iron
Inner Core – Dense solid of iron and nickel

35. ESRT – Pg 10
What happens to the density from the crust towards the inner core?
What happens to pressure as you go towards the core?
What happens to temperature as you go towards the core?
Which layers are liquids (above melting point)?
What is the depth of the boundary between the Mantle & Outer Core?

36. How do we know? From Seismic Waves
Scientists studying earthquakes have found that seismic waves travel through the Earth’s interior at different speeds and directions. The differing speeds are due to the different densities of the existing zones or layers.
Think about trying to run through air vs trying to run through water…
These Seismic Waves are called P (primary) and S (secondary) waves.

37. Seismic Waves
The Seismic Waves change speed and direction as they pass through layers of different densities.
Notice the S-waves do not travel through the liquid outer core…
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