Transcript 501P Inside the Earth PPT

Inside the Earth
Earth’s Shape, Size and
Internal Structure
The earth is round.
Eratosthenes figured
it out in 200 B.C.
He calculated that
Earth’s
circumference was
40,000 km – only off
by 8 km!!
Eratosthenes & the Round Earth
7.2o angle at Alexandria
No angle at Syene (on the
Tropic of Cancer)
Central angle is 7.2o
(1/50th of 360o).
A soldier paced off distance
from Alexandria to Syene
(5,000 stadia = 800 km).
Eratosthenes & the Round Earth
(5,000 stadia = 800 km).
Multiply X 50, you get the
circumference of the Earth:
800 km X 50 = 40,000 km
Actual diameter of the Earth
(pole to pole) = 40,008 km.
Incredibly close for this
method of measuring!
The earth is sort of round –
Oblate Spheroid
Due to its rotation,
Earth bulges slightly
at the equator (about
0.17 % bigger) and is
slightly flattened at the
poles.
It is an oblate
spheroid.
The earth is sort of round –
Oblate Spheroid
Equatorial diameter
is just 0.17 % bigger
than the Polar
diameter.
The earth is tilted at a 22 ½ o angle.
4 Layers of the Earth
Crust
0 – 70 km
thick
2,885 km
thick
2,270 km
thick
2,885 km
5,100 km
Scale
6,400 km
1,216 km
thick
2 Types of Crust
1) Oceanic
Crust
}
5 – 10
km
2) Continental Crust
}
20 – 70
km
}
Two Essentially Different Rock Types
Continental Crust- Granite
Oceanic Crust - Basalt
The Mantle – Thickest Single Layer
Lithosphere –
Crust and
Uppermost
mantle (Solid,
Rigid, Brittle)
Asthenosphere –
Crust and uppermost
mantle (Plastic, weak,
flows like Silly Putty)
Mesosphere - Lower
Mantle (Solid Again)
The “Moho”
The Mohorovičić
discontinuity
(“Moho” for short) is
a sudden, sharp
boundary between
the crust and the
upper mantle.
Increase in P wave
velocity is due to a
sudden increase in
density of the rocks.
Layers of the Mantle
•Lithosphere –
Rigid and Brittle
(partly crust)
•Asthenosphere –
Plastic and
flowing
•Mesosphere
(lower mantle) –
Solid Again
Rocks of the Mantle
Magnetite – Iron Oxide
Olivine Peridotite –
Iron Silicate Minerals
Inner and Outer Cores
Outer Core:
• Liquid Iron
and Nickel
• Hot, but not
as hot as the
inner core
• 2,270 km
thick
Core – Mantle Boundary
•Huge
mountainous
“anticontinents” of
solid mantle
protrude
downward into
the “antioceans” of the
liquid iron
core.
The Two Cores
•Outer Core – Hot
liquid Iron and
Nickel with lumpy
core /mantle
boundary
•Inner Core – Even
hotter but
crystalline Iron
and Nickel
Core Materials
The inner core is thought to be made of crystalline iron
similar to the type we find in iron meteorites. These
distinctive crystal patterns are called Widmanstatten lines.
Thicknesses of the 4 Layers
Crust
0 – 65 km thick
2,885 km
thick
2,270 km
thick
2,900 km
5,100 km
Scale
6,400 km
1,216 km
thick
4 Layers of the Earth