1. So Hot!
Why?
Early Earth 4.6bya

2. Proximity to sun
Accretion

3. Radioactive Decay
Unstable atoms eject nuclear particles, release high energy radiation
gamma waves

4. • Sun’s ignition clears the solar system
• Fewer collisions
• Earth surface begins to cool
• Layers form as Earth cools

5. A Cooled Earth is a Layered Earth
Direct evidence via physical samples from crust, mantle
Indirect evidence for the core
• density calculations
• sun composition, meteorites
• pressure models
• seismic wave behavior
• magnetic field

6. Evidence: Chemical Composition
• Solar spectra tells what elements the Sun is made up of
ex:
• Meteorite samples tell same
• Assuming a common solar system origin:
If we know what elements are in crust & mantle, and in other SS bodies…
The ones ‘missing’ from Earth must be in the core
as evidenced by how Earths perturbs orbits of other bodies

7. Evidence: Element mass
atomic mass
layer(s) O
oxygen 16
crust & mantle Mg
magnesium 24 Si
silicon 28 Fe
iron 56
core Ni
nickel 59
Light elements rise to surface
Heavier ones sink
as evidenced by how Earths perturbs orbits of other bodies

8. Evidence: Differences in Density
Layer
Density
g/cm3
Data Source
Overall
5.5
calculated from Earth’s volume and mass
Continental crust
2.7
direct observations (‘subtract’ from overall)
Oceanic crust
3.0
Mantle
3.9
as evidenced by how Earths perturbs orbits of other bodies
Core deduced from other two
sources

9. Evidence: Seismic Wave Behavior
• Primary (P) and secondary (S) earthquake waves pass through Earth’s interior and are measured by scientists around the world
P (compression wave) S (transverse wave)
as evidenced by how Earths perturbs orbits of other bodies

10. • P and S waves travel at different speeds in different materials: faster through denser rock, slower if there is any melting of the rock
• S-waves are
stopped altogether
by liquid rock
as evidenced by how Earths perturbs orbits of other bodies

11. As the waves encounter different rock types, they refract (bend).
The pattern of wave arrival (‘shadows’) at distant stations reveals that the outer core is liquid, and the inner core is solid
as evidenced by how Earths perturbs orbits of other bodies

12. Evidence: Earth’s Magnetic Field
• Must be a layer that is high in metal elements
• Must be liquid metal to generate an electric current to cause magnetism e- e- e-
spin a factor too
Solar wind? Stream of particle blown off the suns corona
Polarity is the direction of the current, now N e-

13. This magnetosphere protects the Earth from the solar wind
Rocks that form from magma retain a record of the earth;s polarity as the magnetic particles align with the filed when molten.

14. Core conclusions: Both: Largely Fe, Ni metals
Inner – great density & temperature, but also pressure; therefore solid
Outer – great temp but less pressure, therefore liquid; undergoing convection

15. Aurora Borealis
SIDEBAR Where the magnetosphere is thin, near the poles, we see the interaction of the atmosphere, charge e- of the magnetosphere, and the solar wind, causing an Aurora
Aurora Australis
Trapped particles of the solar wind spin around the magnetic field lines
Auroras have been moving, may be evidence of a shift in the earths polarity
Expected every 250,000 years; its been > 780,000!
Auroras are the spectra generated when the particles are energized in collisions with atmosphere

17. Mantle • Thickest layer makes up most of the planet • A fluid solid
• a solid that flows
• albeit very slowly
~cm/year
solid – state of matter
fluid – describes behavior
Olivine rock from the mantle
Like Silly Putty!

18. • The mantle is heated by the core at its base
cool crust
cool mantle
warmed mantle
hot, liquid core
hot, solid core
• The mantle is heated by the core at its base
• mantle is cool near the crust

19. Crust
• Highest in light, less dense elements like Si, lowest in heavy, dense Fe
• Broke into pieces as the planet cooled

20. Two types
continental crust
thick
less dense granitic rock
sea floor crust:
thin
dense basalt rock

21. Alternate Layering Scheme
Crust, plus cooled upper mantle
Deeper, warmer, flowing mantle

23. Infer: Unequal heating of the mantle material causes rock to flow
Rising • cooling • sinking • in a cycle
Drives movement of the plates
radiant energy from decay, residual heat in Earth’s core
Mantle convection
animation

25. Hmmm… Continental shelves align Wegener proposes the continents move
Pangaea

26. Other lines of evidence
Rock deposits
Mountain ranges
Contiguous geology

27. Contiguous fossil distribution

28. Paleoclimate data (paleo = old) Ice sheets over Africa?
No evidence the climate was cold enough to have ice at the equator
Ice sheets once covered now-equatorial landmasses (i.e. Africa) yet no evidence that the climate was cold enough to have ice at the equator