Transcript GLG101online_10B_EarthsInterior_MCC_Leighty

Earth’s Interior
GLG 101 - Physical Geology
Bob Leighty
These notes and web links are your primary “lecture” content in this class.
Additionally, various articles are assigned each week to supplement this “lecture”
information. I believe you’ll have enough information to reference without having
to purchase a costly textbook.
These lecture notes are very similar to the ones I use in my traditional classes.
You’ll find they are loaded with imagery and streamlined text that highlight the
most essential terms and concepts. The notes provide a framework for learning
and, by themselves, are not meant to be a comprehensive source of information.
To take advantage of the global knowledge base known as the Internet, I have
included numerous hyperlinks to external web sites (like the Wikipedia, USGS,
NASA, etc.). Follow the links and scan them for relevant info. The information
from linked web sites is meant to supplement and reinforce the lecture notes –
you won’t be responsible for knowing everything contained in them.
As a distance learning student, you need to explore and understand the content
more independently than in a traditional class. As always, I will help guide you
through this learning adventure. Remember, email Dr. Bob if you have any
questions about today’s lecture ([email protected]).
Leave no questions behind!
Explore and have fun!
Earth’s
Interior
How We Know What’s Inside Earth
 Seismology – Seismic waves provide
a detailed look at Earth's interior
 Petrology – Field & lab studies
 Gravity & magnetic studies
 Theoretical modeling
Earth’s
Interior
How We Know What’s Inside Earth
Seismic Waves
 Wave velocity increases with depth
 Wave paths are interrupted by certain layers (discontinuitues)
Earth’s
Interior
How We Know What’s Inside Earth
Seismic Waves
 These layers have been mapped by seismic reflection (bouncing)
& refraction (bending)
Earth’s
Interior
How We Know What’s Inside Earth
Seismic Waves
 Seismic tomography uses seismic waves to describe Earth's
interior in 3D
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Slow areas (hot) - near volcanic areas, mid-ocean ridges
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Fast areas (cold) - subduction zones, continental interiors
Earth’s
Interior
How We Know What’s Inside Earth
Gravity
 Matter produces a gravity field in all directions
 Inverse-square forces decrease rapidly with distance
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Stronger gravity = Closer and/or more massive
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Weaker gravity = Farther and/or less massive
Earth’s
Interior
How We Know What’s Inside Earth
Gravity
 More mass = stronger gravity
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Higher density rocks = stronger pull
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Lower density rocks = weaker pull
density = mass (g) / volume (cm3)
Earth’s
Interior
How We Know What’s Inside Earth
Gravity
 Variations in Earth’s gravity field = anomalies
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stronger gravity  (+) anomaly
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ore deposits, mafic rocks  (+) anomalies
Earth’s
Interior
How We Know What’s Inside Earth
Gravity
 Variations in Earth’s gravity field = anomalies
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weaker gravity  (-) anomaly
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salt, felsic rocks, basins, craters  (-) anomalies
Earth’s
Interior
How We Know What’s Inside Earth
Magnetism
 Earth has a magnetic field much like a bar magnet
 Earth’s magnetic poles are NOT the same as its geographic
(rotational) poles
Earth’s
Interior
How We Know What’s Inside Earth
Magnetism
 Magnetic polarity = direction of magnetic field lines
 Polarity changes - either “normal” (now) or “reverse”
Earth’s
Interior
How We Know What’s Inside Earth
Magnetism
 Magnetic polarity = direction of magnetic field lines
 Polarity changes - either “normal” (now) or “reverse”
Earth’s
Interior
How We Know What’s Inside Earth
Paleomagnetism
(ancient magnetic fields)
Earth’s
Interior
How We Know What’s Inside Earth
Paleomagnetism
(ancient magnetic fields)
 Example: Mid-Ocean Ridges
Time 1 = Normal polarity
Time 2 = Reverse polarity
Time 3 = Normal polarity
Earth’s
Interior
How We Know What’s Inside Earth
Magnetism
 Magnetic anomalies are useful in finding buried magnetic objects
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more magnetic  (+) anomaly
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ore deposits, mafic rocks  (+) anomalies
Earth’s
Interior
How We Know What’s Inside Earth
Magnetism
 Magnetic anomalies are useful in finding buried magnetic objects
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less magnetic  (-) anomaly
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basins, craters, salt domes  (-) anomalies
Earth’s
Interior
Earth’s Interior
 Solid Fe-rich Inner Core, liquid Fe-rich Outer Core, and a
silicate-rich mantle & crust
Earth’s
Interior
Earth’s Interior
Lithosphere
 Crust + rigid upper mantle = LITHOSPHERE
 The lithosphere is broken into numerous plates (tectonic plates)
 Lithospheric plates slowly move over a weaker mantle layer
(ASTHENOSPHERE)
Earth’s
Interior
Earth’s Interior
Crust
 The lithosphere includes two different types of silicate CRUST:
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Continental crust – Thicker (35 km avg.) & less dense
(more buoyant; higher)
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Oceanic crust – Thinner (7 km avg.) & more dense
(less buoyant, lower)
Earth’s
Interior
Earth’s Interior
Mantle
 Fe- & Mg-rich silicate rock layer forms most of Earth’s volume
 Known only from xenoliths in volcanic rocks, geophysics, and
theoretical & lab studies
Earth’s
Interior
Earth’s Interior
Core
 P-wave shadow zone due to the Core-Mantle boundary
 S-wave shadow zone due to a liquid Fe-rich Outer Core
 Some P-waves are faster due to a solid Fe-rich Inner Core
Earth’s
Interior
Earth’s Interior
Core
 The Dynamo Effect: Earth’s magnetic field is generated by a
rapidly rotating, electrically-conducting & convecting Outer Core
Earth’s
Interior
WWW Links in this Lecture
> Seismology - http://en.wikipedia.org/wiki/Seismology
> Petrology - http://en.wikipedia.org/wiki/Petrology
> Earth’s gravity field - http://en.wikipedia.org/wiki/Earth%27s_gravity
> Earth’s magnetic field - http://en.wikipedia.org/wiki/Earth%27s_magnetic_field
> Seismic waves - http://en.wikipedia.org/wiki/Seismic_wave
> Magnetic north pole - http://en.wikipedia.org/wiki/Magnetic_North_Pole
> Polarity changes - http://en.wikipedia.org/wiki/Geomagnetic_reversal
> Paleomagnetism - http://en.wikipedia.org/wiki/Paleomagnetism
> Mid-ocean ridges - http://en.wikipedia.org/wiki/Mid-ocean_ridges
> Earth’s interior - http://en.wikipedia.org/wiki/Earth_interior
> Lithosphere - http://en.wikipedia.org/wiki/Lithosphere
> Asthenosphere - http://en.wikipedia.org/wiki/Asthenosphere
> Crust - http://en.wikipedia.org/wiki/Crust_%28geology%29
> Continental crust - http://en.wikipedia.org/wiki/Continental_crust
> Oceanic crust - http://en.wikipedia.org/wiki/Oceanic_crust
> Mantle - http://en.wikipedia.org/wiki/Mantle_%28geology%29
> Xenolith - http://en.wikipedia.org/wiki/Xenolith
> Core - http://en.wikipedia.org/wiki/Earth_core#Core
> Shadow zone - http://en.wikipedia.org/wiki/Shadow_zone
> Dynamo - http://en.wikipedia.org/wiki/Dynamo_theory
> Electrical conductor - http://en.wikipedia.org/wiki/Electrical_conductor
> Convection - http://en.wikipedia.org/wiki/Convection