So Hot!
Why?
Early Earth 4.6bya
Proximity to sun
Accretion:
Greater mass, gravity, pressure
Radioactive Decay
Unstable atoms eject nuclear
particles, release high energy
radiation
gamma
waves
• Sun’s ignition
clears the solar
system
• Fewer collisions
• Earth surface
begins to cool
• Layers form as
Earth cools
In your group,
investigate this claim
Elements
Forms
(% abundance)
O (44)
Mg (22)
Si (21)
Fe (6)
SiO2,
MgO,
FeO
oxides
Fe (86)
Ni (4)
Fe;
NiFe
alloy
O (47)
Si (28)
Fe (5)
Mg (2)
SiO2,
MgO,
FeO
oxides
Elements sort into layers based on mass, density

Dynamic Earth
Core
Inner – greatest
density, pressure,
temperature
Solid due to
pressure, despite
heat
Evidenced by volcanism
Outer – less
pressure,
therefore molten
Dense and under
high pressure due in
part due to chemical
composition:
Fe in the inner core;
NiFe alloy in outer
core
More massive, dense
atoms sink to center
of forming planet
Mass
Density
a.m.u. g/cm3
Si
14
2.33
O
16
.001
Mg
24
1.74
Fe
26
7.87
Ni
28
8.9
e-
ee-
ee-
e-
Molten metal of
outer core, plus
Earths axial spin,
creates electric
currents
Currents in turn
create a magnetic
field
earth
This
magnetosphere
protects the earth
from the solar
wind
Where the
magnetosphere is
thin, we see the
interaction of the
atmosphere with
the solar wind
Aurora
Borealis
Evidence for a dense core from
Earth’s own rocks

Crust rocks less dense than the earth as a
whole. (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

Mantle rocks torn off, carried
along with rising mantle
material
Evidence for an iron core from
asteroids


Meteorites are a good chemical match with the sun
This shows that both the sun and the asteroids (the
source of meteorites) were made from the same original
batch of material. By implication the Earth was too.
iron meteorite
Evidence for a solid/molten
inner/outer core from earthquake
wave behavior
Mantle
Mantle
Outer
core
• Less Fe than core;
more MgO than
crust
Density
g/cm3
MgO
3.58
SiO2
2.65
Mantle
• Heated by the core at
its base, creating
convection
• A fluid solid - albeit
flowing very slowly
solid – state of matter
fluid – describes behavior
Like Silly Putty!
Crust
• Broken into plates, the
result of shrinking as the
planet cooled
• Highest in SiOx, lowest in
FeO, MgO
continental
shelf
• Thin oceanic
crust & thicker,
less dense
continental crust
continental
crust
sea floor crust
Alternate Layering Scheme
Rigid crust
and upper
mantle
warmer, flowing mantle
Hmmm…
Continental
shelves
align
Wegener proposes
the continents move
Pangaea
Other lines
of evidence
Rock
deposits
Contiguous
geology
Mountain
ranges
Contiguous fossil distribution
Paleoclimate data
(paleo = old)
Ice sheets
over Africa?
No evidence
the climate
was cold
enough to
have ice at the
equator
Infer: Unequal
heating of the
mantle material
causes rock to
flow
Rising • cooling •
sinking • in a
cycle
Drives movement
of the plates
Mantle convection
animation
radiant energy from
decay in Earth’s core