1. So Hot!
Why?
Early Earth 4.6bya

2. Proximity to new sun
Accretion:
Collisions > greater mass, gravity, pressure

3. The Sun Forms • Clears the solar system collisions
Therefore fewer
collisions
• Earth’s surface begins
to cool
• water vapor escapes,
condenses into clouds,
rain, furthering the
cooling
In the very beginning of earth's history, this planet was a giant, red hot, roiling, boiling sea of molten rock - a magma ocean. The heat had been generated by the repeated high speed collisions of much smaller bodies of space rocks that continually clumped together as they collided to form this planet. As the collisions tapered off the earth began to cool, forming a thin crust on its surface. As the cooling continued, water vapor began to escape and condense in the earth's early atmosphere. Clouds formed and storms raged, raining more and more water down on the primitive earth, cooling the surface further until it was flooded with water, forming the seas.
A cooling Earth

4. • Residual heat from formation • Radioactive decay of unstable atoms
Inner planet remains hot
• Residual heat from formation • Radioactive decay of unstable atoms
In decay, atoms eject nuclear particles and release high energy (gamma) radiation

5. Layers form
Cooling Earth differentiates into layers:

7. Core Inner – greatest density, pressure, temperature
Solid due to pressure, despite heat
Outer – less pressure, therefore molten
Evidenced by volcanism

8. Evidence for an iron core from meteorites
Abundance of elements in meteorites reflects the abundance of elements everywhere in the early solar system, Earth included
Once the volatiles are burned off, an iron core remains
GEOCHEMISTS have frequently used the abundances of elements in meteorites as a guide to the overall composition of the Earth. The abundances in the chondritic meteorites have been commonly used on the assumption that they represent the closest approach to the composition, for the non-volatile elements, of the primitive unfractionated material in the solar system.
iron meteorite
Russia, 2013

9. Evidence for a dense core from direct observation of rocks
Crust/mantle rocks less dense than the earth as a whole (crust: 2.8g/cc vs 5.5g/cc)
the interior must be made
of a material whose density
is considerably greater than
Earth’s average density to
compensate
enoliths are formed when magma rising from deep levels rips off pieces
of the rock which it passes through (the
country rock
) and carries these pieces along with it.
Mantle rocks torn off, carried along with rising mantle material

10. Evidence for dense metal core inferred from chemical composition
More massive, dense, atoms sink to center of forming planet
Mass
a.m.u.
Density
g/cm3 Si 14
2.33 O 16
.001 Mg 12
1.74 Fe 26
7.87 Ni 28
8.9
Fe in the inner core; NiFe alloy in outer core

11. Evidence for molten metal outer core from the magnetic field
Earths axial spin, creates electric currents in outer core
Currents in turn create a magnetic field e- 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- e-
Cartoon explanation
100 greatest discoveries

12. Magnetic field has reversed over time, repeatedly, leaving a record in the rocks.
cooled rocks, magnetic particles ‘frozen’
Sea floor has an extensive record of the reversals

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. Where the magnetosphere is thin, we see the interaction of the atmosphere with the solar wind
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
Aurora Borealis

15. Evidence for a solid/molten inner/outer core from earthquake wave behavior
S-waves do not transmit
through fluids, or the
outer core

16. Mantle Mantle • Mid-density SiO2 2.65 MgO 3.58 Ni & Fe 9.9
Less Fe than core
More MgO than crust
Less SiO2 than crust
Mantle
Density
g/cm3
SiO2
2.65
MgO
3.58
Ni & Fe
9.9

17. • Heated by the core at its base, cool at the crust, creating convection currents • A fluid solid - albeit flowing very slowly
solid – state of matter
fluid – describes behavior
Olivine from the mantle
Like Silly Putty!

18. Crust
Density
g/cm3
SiO2
2.65
MgO
3.58
NiFe
9.9
• Broken into plates as the planet cooled, shrank
• Highest in SiO2, lowest in FeO, MgO

19. • Broken into plates as the planet cooled, shrank
• Highest in SiO2, lowest in FeO, MgO
• Two types:
sea floor crust:
thin, basalts
continental crust:
thick, granitic

20. Last word… …percent abundance crust mantle SiO2 60.6 46 MgO 4.7 37.3
FeO
6.7
7.5

21. Alternate Layering Scheme
lithosphere
Rigid crust plus upper mantle
asthenosphere
warmer mantle