Download EARTH`S INTERIOR

EARTH’S INTERIOR
I.
Earth’s Interior
Geologists are not able to sample rocks very far below Earth’s surface. Some deep mines are 3 km deep
and a deep oil well may have a depth of 8 km. The deepest scientific well has reached 12 km in Russia.
Clearly, studies of Earth’s interior must be from analysis of indirect information. Geophysics is the
branch of geology that applies physical laws and principles to a study of Earth. Geophysics includes the
study of seismic waves, Earth’s magnetic field, gravity, and heat.
A.
Evidence From Seismic Waves
1.
Seismic __________________
a.
Return of some energy to Earth’s surface from a boundary
b.
Boundary between two layers of differing density
2.
Seismic ___________________
a.
Bending of Seismic Waves
b.
Occurs only if velocity differs in each layer (caused by density differences)
3.
First and Second Arrival Seismic Waves
a.
b.
B.
Deeper Wave _________________ and arrives at a seismograph station first.
Can infer depth of boundaries between layers
Earth’s Internal Structure
1.
Crust
a.
Outer thin layer (varies from 7 km to 50 km in thickness)
b.
Mohorovi…iƒ Discontinuity (called the ____________)
(1)
A discontinuity is a boundary where seismic waves experience an abrupt
change in velocity or direction
(2)
Separates the crust from the mantle
2.
Mantle:
a.
Upper Mantle: Part of the _____________________:
(1)
Crust and Upper Mantle
(2)
Outer shell of Earth and is strong and brittle
b.
ESC 101: Professor Vorwald
__________________________
(1)
Low-Velocity Zone
(2)
Extends to 200 km depth
(3)
Rocks close to melting point (1 to 10% molten)
(4)
Rocks may have little strength and be capable of flowing (slippery and
mobile layer on which overlying plates can move
Earth’s Interior Notes
Page 1 of 3
c.
3.
Lower mantle
(1)
Consists mostly of silicates and oxides of magnesium and iron (ultramafic
rocks)
(2)
Rearranged into denser and more compact crystals
The Core
a.
_____________ Zones:
(1)
(2)
(3)
b.
II.
Seismic Waves do not reach certain areas on the
opposite side of Earth from a large Earthquake
P-wave shadow zone
(a)
Refraction of P-waves when they encounter the core boundary
(b)
Size and shape of core can be determined because the paths of Pwaves can be accurately determined.
S-Wave Shadow Zone
(a)
Larger than the P-wave shadow zone
(b)
Direct S-Waves are not recorded in the entire region more than
103o from the epicenter
(c)
Indicates that S-waves do not pass through the core at all
Conclusions
(a)
Infer that the core has _________ parts
(b)
Outer core is ______________
(c)
Inner core is a _____________ iron crystal
Composition
(1)
Density is very high when averaged with crust and mantle
(2)
Evidence for iron
(a)
Meteorites may represent basic material that created the solar
system and 10% are composed of Fe and Ni (may represent the
cores of fragmented planetismals and asteroids)
(b)
Seismic and density data along with assumptions based on
meteorite composition, point to a largely iron core.
(c)
The presence of Earth’s magnetic field also suggests a metallic
core.
Isostasy
A.
B.
C.
D.
E.
Balance or ________________________ of adjacent rocks of brittle crust that float on the plastic
mantle.
Areas that loss mass __________.
Areas that gain mass __________.
Isostatic Adjustment
1.
_____________________ Movement to reach equilibrium
2.
Depth of equal pressure: Depth where each column of rock is in balance with others
(same weight).
Crustal Rebound
1.
____________________ movements of crust
2.
Loss of huge mass of ice at the end of the Pleistocene epoch
ESC 101: Professor Vorwald
Earth’s Interior Notes
Page 2 of 3
III.
Gravity Measurements
A.
B.
C.
IV.
Force of gravity is affected by the _______________ between two masses and the masses of the
two objects
Gravity Meter (Gravitometer):
Measures the gravitational attraction between Earth at a
specific location and a mass within the instrument
Gravity is Affected by
1.
__________________ rock underground (such as metallic ore deposits)
2.
Degree of isostatic equilibrium of a region
D.
Positive Gravity Anomaly
1.
__________________ than normal gravity meassurements
2.
Can indicate location of metallic subsurface ores and rocks
3.
Can indicate that tectonic forces are holding up a region and is not in isostatic balance.
a.
Uplift may have created a mountain range without a mountain root.
b.
There is a thicker section of denser mantle rock under the mountain range.
c.
The central “column” has more mass.
E.
Negative Gravity Anomaly
1.
A region with _________ gravity.
2.
Can be cause by:
a.
A region being held down (mass deficiency)
b.
Low density subsurface rocks (such as salt deposits)
c.
Large underground caverns.
F.
Isostatic Balance
1.
Uniform gravity readings
2.
Corrections made for difference in elevation.
Earth’s Magnetic Field
A.
Believed to be generated in the ____________ core by
1.
Hot liquid outer core flows and convecting metal creates electric currents
2.
Currents with Earth’s rotation create a magnetic field
B.
C.
Magnetic Reversals: Evidence in sea-floor rocks
Magnetic Anomalies
1.
Positive Magnetic Anomalies
a.
__________________ than normal reading
b.
Can be caused by
(1)
concentration of magnetite ore
(2)
Concentration of ferromagnesium minerals in mafic rocks
(3)
Hidden geologic structures
2.
Negative Magnetic Anomalies
a.
__________ than normal reading
b.
Can be caused by downdropped fault blocks
ESC 101: Professor Vorwald
Earth’s Interior Notes
Page 3 of 3