1. Earth’s Structure
View of Earth from moon. We know what the surface of the Earth looks like. What does the inside look like?

2. Origin of the Earth Earth is 4.6 billion years old
Meteors and Asteroids bombarded the Earth
Earth is 4.6 billion years old
Our early Earth grew from a barrage of extraterrestrial impacts, increasing in mass over time. In the early stages of planetary accretion, the Earth was much less compact that it is today. The accretionary process led to an even greater gravitational attraction. Gravitational energy converted into heat. Radioactive elements are unstable, and over time become more stable. Radioactive decay processes releases heat. U-238 to Pb Initial accretion led to a homogeneous sphere that eventually became density stratified with the heavier iron and nickel sinking to the center of the earth, and the lighter silicates (rocky) floated to the top.

3. Earth’s Interior Core Mantle Crust dense Iron and Nickel
Inner Core - solid
Outer Core - liquid
Mantle
Less dense than core
Iron and Magnesium silicates
Mostly solid
Upper mantle is partially molten
Core – composed of two parts. The core is very dense and composed mostly of Iron and Nickel. The inner core is solid. This is because there is so much pressure exerted that it can only exist in the solid form. The outer core is liquid iron and nickel. Again, it is very dense but because it is in its liquid form it is less dense than solid and forms the outer core.
Mantle is composed of Iron and Magnesium silicates (Si + O). It is mostly solid, but the uppermost part of the mantle is partially molten (slush – where you do have liquid and solid mixed). Now, this is very important in plate tectonics.
Crust –This is the outermost layer. It is very thin and rigid. Rigid means that it is a solid. If you can imagine an apple. It would have the thickness of the skin of an apple. There is two types of crust – continental crust and oceanic crust.
Important notes:
Thin crust + uppermost mantle is rigid. This forms the “lithospheric plates”.
partially molten mantle acts as a lubricant. This enables the plates to move freely along the surface of the Earth.
Crust
Outermost layer
Very thin and rigid
Continental – granite
Density = 2.8 g/cm3
Oceanic – basalt
Density = 3.0 g/cm3

4. Earth’s Interior
Lithosphere - The rigid portion of the Earth’s crust (both oceanic & continental) that is broken into plates.
“Litho” comes from the Greek word meaning rock
Asthenosphere – the slushy (partially liquid & solid) in the upper mantle on which the plates “float”
“Asthenes” comes from the Greek word meaning weak

5. Types of Seismic Waves P waves S waves Primary waves
Push and pull movement
Travel fastest (~ 6 km/sec)
Travel thru solids and liquids
S waves
Secondary waves
Move side-to-side
Slower (~ 4 km/sec)
Travel thru solids only

6. Continents Today

7. Continental Drift Theory
In 1912 a German meteorologist, astronomer and explorer named Alfred Wegener presented a theory that the continents were once joined together in one land mass and have over millions of years slowly drifted apart into their present positions as we see them today. He named the supercontinent “Pangaea” after the Greek word meaning “all land”.

8. Continental Drift Geographic Fit
About 210 Ma, Pangaea began to break apart.
Continents seem to fit together like pieces of a puzzle

9. Continental Drift Theory
Through Wegener’s research he found evidence to support his theory:
Fossils of Glossopteris, a seed fern, was found in India, Australia, South America, Africa and Antarctica
Fossils of Mesosaurus, a small reptile were found in freshwater deposits in Africa & South America.

10. Continental Drift Fossils
Studies were done on land animals that could not swim. Once continents split, evolution occurs. Organisms begin to differentiate. Climate is different, food sources are different, predators are different.
Similar distribution of fossils such as the Mesosaurus

11. Glossopteris
Fern

12. Continental Drift
Layers of the mountains found in S.E. Brazil, South America and S.W. Africa line up layer for layer in exact format.
Continents look like puzzle pieces that could fit together.

13. Continental Drift Mountains
If you were to put the puzzles back together, mountain chains match up, i.e., Appalachian Mtns, British Isles, and Caledonian Mtns.
Mountain ranges match across oceans

14. Continental Drift Glaciation
Glaciers typically occur near the poles. We are in a warm period, but in the past it was cool and ice caps grew. Deposits related to glaciers were deposited. You also find glacial deposits in Africa near the equator. How to you get glacial deposits near the equator?
Glacial ages and climate evidence

15. Continental Drift Glaciation
Glaciers typically occur near the poles. We are in a warm period, but in the past it was cool and ice caps grew. Deposits related to glaciers were deposited. You also find glacial deposits in Africa near the equator. How to you get glacial deposits near the equator?
Glacial ages and climate evidence

16. Continental Drift Model Problems
Alfred Wegener
Presented research to professionals
Did not provide a plausible mechanism to explain how continents drifted
Wegener was a scientist. Scientists go to scientific meetings to present their research. When Wegener presented his research to other physicists, they did not agree. They wanted to know how do continents drift? There was no driving mechanism to support continental drift. Wegener could not answer “how” so his Continental Drift Model was not accepted.

17. Seafloor Spreading
Continental drift reexamined in 1960’s with new information
New theory developed – Seafloor spreading
Supporting evidence for seafloor spreading
World seismicity
Volcanism
The 1960’s is relatively recent. Geology is a new science compared to Physics, Chemistry and even Biology. People were doing separate studies about earthquakes, volcanoes, age of sea floor, paleomagnetism. Someone put it all together. A new theory developed – Seafloor Spreading. There were a lot of evidence to support Seafloor spreading.
Age of seafloor
Paleomagnetism
Heat flow
Theory combining continental drift and seafloor spreading termed “Plate Tectonics”

18. Principles of Plate Tectonics
Earth’s outermost layer composed of thin rigid plates moving horizontally
Plates interact with each other along their edges (plate boundaries)
Plate boundaries have high degree of tectonic activity
mountain building
earthquakes
volcanoes