Transcript Document

Which of the following statements regarding what
we know about Earth’s interior is most
accurate?
A) We have been able to drill into the earth’s core
B) Much about what we know about Earth’s mantle
and core comes from caves and mines
C) We know only about what is on the very surface
of the earth, in what is known as the crust
D) Energy waves allow us to see precisely what is
deep inside the Earth, like a “tricorder” or
scanner from
Star Trek
Earth’s Interior
What we know about Earth’s interior comes
from indirect avenues of investigation.
Earth’s diameter is approximately 12,756 km
(~ 7,500 miles).
-the deepest hole we have ever drilled
into the Earth is only 9.6 km (~5 mi).
so how do we know what it’s like?
Seismic waves! - natural and man-made
Earthquakes
seismic (energy) waves travel through the earth
some energy bounces off harder layers
called reflection
some energy travels through but gets bent,
changing the direction the wave is traveling
called refraction
some energy is absorbed as it encounters
materials
called attenuation
Allow us to model what waves show up at given
locations, and when they arrive at given locations.
Shallow high frequency seismic waves allow us to
see reflectors and refractors at depth
Wave paths are
influenced by
density,
temperature, and
the angles at which
they strike
boundaries as they
travel through and
around the Earth
Factors affect seismic waves
distance: farther = more attenuation
density: higher = faster
temperature: colder = faster
liquid vs solid
- solid = faster; p-waves and s-waves
- liquid = slower; no s-waves
angle of incidence- controls how much is
reflected and how much is absorbed
vertical arrangement of layers
- controls the resultant direction of travel
P-wave and S-wave shadow zones
- caused by transmissive and refractive properties
of the waves interacting with rock and liquid
Zones of material with distinctive characteristics
make up each layer in the Earth
Greatly
simplified it
looks like
concentric
spheres
Crust- the rigid outer shell of the Earth,
composed of solid rock; very thin- averages only
20 km thick (the crust is part of the Lithosphere)
two kinds of crust
Oceanic- most abundant; consists of rocks formed
from mafic magma; very dense; very thin- 10 km
thick
Continental- underlies continents; consists of rock
formed from felsic and intermediate magma; less
dense than oceanic crust; thick-30 to 85 km thick
What will happen as different kinds of crust
interact with each other?
A) Oceanic and Continental - ?
B) Old Oceanic and Younger Oceanic - ?
C) Continental and continental - ?
Model of Lithosphere and Aesthenosphere showing
thickness of Oceanic vs Continental crust
Continental crust
Oceanic crust
Uppermost mantle- Aesthenosphere
Mohorovicic Discontinuity
“The Moho”
Isopach contour lines = lines of equal thickness of
the crust
The boundary zone between the crust and the
mantle is called the Mohorovicic Discontinuity or
the “Moho”
- a zone of low velocity transmission of seismic
waves
Mantle- the semi-solid (jello-like) material
underlying the crust. Extends down to about
3000 km depth
The uppermost part of the mantle is called the
Aesthenosphere.
mostly molten material
The mantle is heated closer to the core
Heated mantle material rises upward very slowly
millions of years to move upward
As it near the earth’s surface, the mantle
material liquefies
(due to pressure and temp relationships)
It also begins to cool, and slowly starts to sink
back into the core
This creates a Convection current
Two highly
schematic models
of
mantle convection
currents
3D models of mantle
convection currents
Heated rising
material
Cooled sinking
material
3D maps of the earth’s convection currents based
on seismic wave analysis-complicated looking!
Earth’s core
Divided into an inner and outer zone
Outer zone is liquid- doesn’t transmit s-waves
Probably composed of Nickel (Ni) and Iron (Fe),
some heavier radioactive elements, along with some
other elements (S or N- Sulfur or Nitrogen)
Inner core is solid- based on speed of P-wave travel
composed of same materials as outer core
Important for generating Earth’s magnetic field
Earth’s magnetic field is created by the rotation
of the outer fluid core around the solid inner core
This creates an
electrical current
Generates an
electromagnetic
Field.
Similar to a
bar magnet with
a positive and
negative end
Earth’s magnetic field fluctuates over time due to
the unsteady nature of the geodynamo that is the
the outer and inner core
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Earth’s magnetic field interacts with solar
particles, forcing them to the north or south pole,
creating the Aurora Borealis
Earth’s magnetic field plays a vital role in
the development of Plate tectonics theory
Identification of a process that
allows for Sea Floor Spreading.