Earth’s Interior Bob Leighty GLG 101 - Physical Geology.

GLG 101 - Physical GeologyGLG 101 - Physical Geology Bob LeightyBob Leighty

Earth’s InteriorEarth’s Interior

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!Explore and have fun!

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.

Seismology – Seismic waves provide a detailed look at Earth's interior

Gravity & magnetic studies

Petrology – Field & lab studies

Theoretical modeling

How We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’sInteriorInterior

Seismic WavesSeismic Waves

Earth’sEarth’sInteriorInterior

Wave velocity increases with depth Wave paths are interrupted by certain layers

(discontinuitues)

How We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’sInteriorInterior

These layers have been mapped by seismic reflection (bouncing) & refraction (bending)

How We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’sInteriorInterior

Seismic WavesSeismic Waves

Seismic tomography uses seismic waves to describe Earth's interior in 3D> Slow areas (hot) - near volcanic areas, mid-ocean ridges> Fast areas (cold) - subduction zones, continental interiors

Seismic WavesSeismic WavesHow We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’s

InteriorInterior

Inverse-square forces decrease rapidly with distance

Matter produces a gravity field in all directions

> Stronger gravity = Closer and/or more massive

> Weaker gravity = Farther and/or less massive

GravityGravityHow We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’s

InteriorInterior

More mass = stronger gravity

density = mass (g) / volume (cm3)

> Higher density rocks = stronger pull

> Lower density rocks = weaker pull

GravityGravityHow We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’s

InteriorInterior

Variations in Earth’s gravity field = anomalies

> ore deposits, mafic rocks   (+) anomalies

> stronger gravity   (+) anomaly

GravityGravityHow We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’s

InteriorInterior

Variations in Earth’s gravity field = anomalies

> salt, felsic rocks, basins, craters   (-) anomalies

> weaker gravity   (-) anomaly

GravityGravityHow We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’s

InteriorInterior

Earth has a magnetic field much like a bar magnet

How We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’sInteriorInterior

MagnetismMagnetism

Earth’s magnetic poles are NOT the same as its geographic (rotational) poles

Polarity changes - either “normal” (now) or “reverse” Magnetic polarity = direction of magnetic field lines

How We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’sInteriorInterior

MagnetismMagnetism

Polarity changes - either “normal” (now) or “reverse” Magnetic polarity = direction of magnetic field lines

How We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’sInteriorInterior

MagnetismMagnetism

How We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’sInteriorInterior

PaleomagnetismPaleomagnetism(ancient magnetic fields)(ancient magnetic fields)

Example: Mid-Ocean Ridges

Time 2 = Reverse polarity

Time 1 = Normal polarity

Time 3 = Normal polarity

How We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’sInteriorInterior

PaleomagnetismPaleomagnetism(ancient magnetic fields)(ancient magnetic fields)

Magnetic anomalies are useful in finding buried magnetic objects

> ore deposits, mafic rocks   (+) anomalies

> more magnetic   (+) anomaly

How We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’sInteriorInterior

MagnetismMagnetism

> basins, craters, salt domes   (-) anomalies

Magnetic anomalies are useful in finding buried magnetic objects

> less magnetic   (-) anomaly

How We Know What’s Inside EarthHow We Know What’s Inside EarthEarth’sEarth’sInteriorInterior

MagnetismMagnetism

Solid Fe-rich Inner Core, liquid Fe-rich Outer Core, and a silicate-rich mantle & crust

Earth’s InteriorEarth’s InteriorEarth’sEarth’sInteriorInterior

Crust + rigid upper mantle = LITHOSPHERE The lithosphere is broken into numerous plates (tectonic

plates)

LithosphereLithosphere

Lithospheric plates slowly move over a weaker mantle layer (ASTHENOSPHERE)

Earth’s InteriorEarth’s InteriorEarth’sEarth’sInteriorInterior

> Continental crust – Thicker (35 km avg.) & less dense (more buoyant; higher)> Oceanic crust – Thinner (7 km avg.) & more dense (less buoyant, lower)

The lithosphere includes two different types of silicate CRUST:

CrustCrustEarth’s InteriorEarth’s InteriorEarth’sEarth’s

InteriorInterior

Known only from xenoliths in volcanic rocks, geophysics, and theoretical & lab studies

Fe- & Mg-rich silicate rock layer forms most of Earth’s volume

MantleMantleEarth’s InteriorEarth’s InteriorEarth’sEarth’s

InteriorInterior

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

CoreCoreEarth’s InteriorEarth’s InteriorEarth’sEarth’s

InteriorInterior

The Dynamo Effect: Earth’s magnetic field is generated by a rapidly rotating, electrically-conducting & convecting Outer Core

CoreCoreEarth’s InteriorEarth’s InteriorEarth’sEarth’s

InteriorInterior

WWW Links in this LectureWWW 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

Earth’sEarth’sInteriorInterior