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How Do We Know What It Is Like Inside The Earth?

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How Do We Know What It Is Like Inside The Earth? Pre-GPT scientific thought on the Earth before 1950 Department of Geological Sciences San Diego State University – PowerPoint PPT presentation

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Title: How Do We Know What It Is Like Inside The Earth?


1
How Do We Know What It Is Like Inside The Earth?
  • Pre-GPT scientific thought on the Earth before
    1950
  • Department of Geological Sciences
  • San Diego State University

2
What direct evidence tells you about the inside
of the Earth?
3
How Symmetrical Is the Earth?
4
How Symmetrical Is the Earth? Very, a the
rotation about its axis is fairly smooth
Symmetry would be imposed by initial
spinning while molten
Any reasonable Earth model proposed must be
symmetrical
5
The Interior Temperature of the Earth
  • Is the inside of the Earth hot or cold?
  • What evidence is there for this?

6
Evidence that the Earth is hot inside
Hot Geysers
Volcanoes
Hot sulfurous gasses from vents
7
Deep Mines
Evidence that the Earth is hot inside
The temperature in all deeper mines increases
with depth About 30 oC per 1000
m
This image is in a South African Gold mine 3km
or 2 miles deep in the Earth. The temperature is
49 C or 120 F
The limit to the depth of a deep mine is when the
temperature is to hot for stand
Deepest mine is 3,585 m or 11,762 ft
8
Deepest mines only extend a tiny fraction into
the average thickness the crust, never mind the
rest of the Earth
Deepest Mine 3.4 km
.
Earth Radius 6,400 km
9
What About Magnetism?
  • Is the Earths magnetic?
  • What sort of properties does it have?
  • Could you detect the Earths magnetic field

10
The Earths Magnetic Field by compass
Age of Exploration, 1400-1600, also discovered
the compass and Earths magnetic field.
11
Magnetic Dip the angle that magnetic lines leave
or enter the Earth
12
Aurora Borealis and Aurora Australis, northern
and southern lights
13
Most frequent is near 67 N and S latitude
Maximum N. Pole Coverage
Earths magnetic field must be deep inside, And
uniform and symmetrical to cause symmetrical
compass variations and the Auras Borealis and
Australis
Maximum S. Pole Coverage
14
What can gravity tell us about the Earth?
I am So proud
Sir Isaac Newton Published his Philosophiae
Naturalis Principia 1686 which included the
definitive statement on gravitation
15
Basic Gravity
Any two bodies in the universe attracted each
other with a force that is GREATER if either is
more MASSIVE GREATER if they are CLOSER
Hey, this Took a lot of work
Force, equal and opposite
Force, equal and opposite
16
Gravity The Formula
G
Memorize this for the quiz
m2
D
m1
17
Cavendishs 1789 Experiment to Determine the
Mass and Density of the Earth
Earth mass
Ball mass
Use torsion balance to measure the force
between 4 iron balls Measure the size and mass
of the iron balls Calculate constant in
gravity formula
G
Ball weight
Earth
Earth Radius
Earth Mass 6 x 10 24kg
Earth Average Density 5.54 g/cm3
18
Cavendishs 1789 Experiment to Determine the
Mass and Density of the Earth What does this
mean?
Earth Average Density 5.54 g/cm3
Earth
You should see this on my Facebook
Henry Cavendish 1789
19
Cavendishs 1789 Experiment to Determine the
Mass and Density of the Earth What does this
mean?
Water 1 g/cm3
Earth
Surface rocks as Basalt, Granite 3 g/cm3
Earth Average Density 5.54 g/cm3
Deeper Rocks must be much denser than 5.54
g/cm3 to compensate for lighter surface rocks
20
What is the material at the center of the Earth?
Iron -Nickel
The Earth is thought to be similar to
Meteorites, about 5 of the meteorites are
Iron-Nickel metal. These are believed to have
been the center of former bodies in space where
the Iron-Nickel, a dense material, settled
to the center when the body was molten. A later
collision broke apart the body into many small
parts.
Iron-Nickel meteorite found in Oregon
21
Gravity is significantly affected by masses close
to the Earths surface even only a kilometer
or so under ground
Earths Radius 6,500 km
22
Ore bodies near the surface will cause gravity to
be more and less a way of searching for them
23
The British Great Arc Meridian Survey of India
1803-50
24
The British discovered that their plumb bobs
were not pointing toward the center of the Earth
What could be an explanation?
25
Plum bobs, gravity and floating
George Airy
John Pratt
Airy and Pratt proposed different explanations
for the nature of the crust. Airy hypothesized
that there was a uniform density crust to
the Earth and it varied in thickness he was
more right.
26
Isostasy and Floating Analogy The crust floats
on the mantel. A plate floats on a portion of
mantle.
Figure 2-5
27
Crust, Mantle, Core, Plates all - float with
lighter on top, heavier below Just as objects do
in water
Principle of Isostacy A body that is less dense
than a surrounding fluid will displace a volume
of the fluid equal to that bodys mass
28
What Can Sound Tell Us?
Hint Earthquakes are mostly sound energy
Earthquakes are used to probe the interior of
the Earth, somewhat as a bat uses sound not only
to detect the presence of objects but about the
objects size and nature.
29
(Garrison, 1993)
30
Prediction for Homogeneous Earth Structure
Observation from Global Seismological Networks
(Garrison-3.7Top)
(Garrison, 1993)
31
(No Transcript)
32
.
33
Connect the dots Then you get curves
of temperature, density, P and S speed,
properties and molecules
Crust
34
The End
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