1. Earth Formation, Earth Layers, & Plate Tectonics
Earth’s beginning:
Most accepted scientific theory dates the Earth at _4.6_ billion years old.
Scientists determined the age of Earth by dating Precambrian zircon crystals in rocks at _4.4 _ billion years old, moon rocks at __4.45_ billion years old, and meteorites which range from _4.5_ – _4.7_billion years old

2. The early Earth was a hot, molten ball
Sources of internal heat:
1. Gravitational Contraction: as Earth’s mass grew, gravity
caused the mechanical energy of contraction to be converted
to thermal energy.
2. Radioactive Isotopes released (and still do release)
thermal energy as the isotopes go through radioactive decay.
3. Bombardment by Asteroids and Meteors also caused
mechanical energy to be converted into thermal energy .
(2 ½ minute video on Earth’s birth)

3. As Earth cooled, crust formed as its upper layer solidified.
These early crust pieces returned to the mantle carrying water which when recycled produced a less dense, granitic crust.
Differentiation: Layering of the Eearth as it cooled due to differences in density, (iron sank) while Earth was still in a molten phase.
First water & atmosphere:
As earth cooled the raw materials for water and an atmosphere emerged due to geologic activities (i.e. volcanoes, geysers, rifts, trenches, etc.) + comets & meteors.
(10½ minute video: Earth's formation and history)

4. Earth’s Layers
Two things increase the closer to the center of the Earth (core) we go:
Density: mass per unit volume.
(how closely packed matter is in a space)
2. Temperature: (It gets Hotter!!!)
Main layers of the Earth:
Crust
Mantle
Outer Core
Inner Core

5. The Crust (Lithosphere)
Solid: Made up of Silicates. (very light material)
Oceanic crust is more dense (Basaltic).
Continental crust is less dense (Granitic).
8-40 km thick.
Temperature increases at
1ºC per 40 m after 1st 20 m

6. The Mantle Middle, semi-solid hot rock layer; composed of
mostly silicates, but is also rich in iron and
magnesium which makes it more dense than
the crust.
It has Plasticity; which is the ability of a solid to flow.
2900 km thick
Asthenosphere – upper layer
that the lithosphere floats on.
Mesosphere – the lower layer
Temperature ranges from
870 ºC ºC
(1 minute convection video)

7. The Core: center of Earth
Outer Core – liquid
2250 km thick
2200 ºC – 3200 ºC
Inner Core – solid due
to extreme pressure
1300 km thick
3200 ºC – 5500 ºC

8. Plate Tectonics
If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.
In 1910, Alfred Wegener’s proposed Continental Drift: the hypothesis that Earth’s plates are floating on the mantle in a slow & steady motion caused by convection currents.
Pangaea– the name given to the single land mass that split and moved apart about 200 mya to form today’s continents. (means all lands)
(Continental Drift video: 1 ½ min.)
(future drift video: 1 minute)

9. Evidence for continental drift and Pangaea
Landforms – shape of continental coastlines, mountain ranges, coal fields, etc.
Fossils – same plant & animal fossils on continents now separated by water.
Climate – tropical plant fossils in cold climates today {Spitsbergen Norway & Antarctica} & glacier tracks in rocks in warm climates today {Africa, S.A., Australia & India}
4. Magnetic reversal of polarity
stripes in rocks in the ocean
floor crust.
Satellite &
Sonar data

10. Plate Tectonics: The earth’s crust is divided into tectonic plates which move in various directions.

11. 3 Types of Plate Boundaries:
1. Divergent Boundary: plates move apart creating
new crust (rift valley & mid-ocean ridge) ← →

12. 2. Convergent Boundary: plates collide and destroy or
buckle crust (move together) → ←
Oceanic-Oceanic: subduction of one
plate under another creating trenches
& volcanic islands
Oceanic-Continental: oceanic (more dense)
subducts under continental (less dense)
creating trenches & volcanic mountains.
Continental-Continental: compression
and buckling forms tall folded mountains.

13. 3. Transform Boundary: plates sliding side-to-side
(creates faults & earthquakes) ↑↓
(plate boundaries animation)