Earth’s Interior Bob Leighty GLG 101 - Physical Geology

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 (rleighty@mail.mc.maricopa.edu). Leave no questions behind! Explore and have fun!

How We Know What’s Inside Earth Earth’s Interior Seismology – Seismic waves provide a detailed look at Earth's interior Theoretical modeling Petrology – Field & lab studies Gravity & magnetic studies

How We Know What’s Inside Earth Earth’s Interior Earth’s Interior How We Know What’s Inside Earth WWW Seismic Waves Wave velocity increases with depth Wave paths are interrupted by certain layers (discontinuitues)

How We Know What’s Inside Earth Earth’s Interior How We Know What’s Inside Earth Seismic Waves These layers have been mapped by seismic reflection (bouncing) & refraction (bending)

How We Know What’s Inside Earth Earth’s Interior How We Know What’s Inside Earth Seismic 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

How We Know What’s Inside Earth Earth’s Interior WWW Gravity Matter produces a gravity field in all directions Inverse-square forces decrease rapidly with distance > Stronger gravity = Closer and/or more massive > Weaker gravity = Farther and/or less massive

How We Know What’s Inside Earth density = mass (g) / volume (cm3) Earth’s Interior Gravity More mass = stronger gravity > Higher density rocks = stronger pull > Lower density rocks = weaker pull density = mass (g) / volume (cm3)

How We Know What’s Inside Earth Earth’s Interior Gravity Variations in Earth’s gravity field = anomalies > stronger gravity   (+) anomaly > ore deposits, mafic rocks   (+) anomalies

How We Know What’s Inside Earth Earth’s Interior Gravity Variations in Earth’s gravity field = anomalies > weaker gravity   (-) anomaly > salt, felsic rocks, basins, craters   (-) anomalies

How We Know What’s Inside Earth Earth’s Interior WWW Magnetism Earth has a magnetic field much like a bar magnet Earth’s magnetic poles are NOT the same as its geographic (rotational) poles

How We Know What’s Inside Earth 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”

How We Know What’s Inside Earth 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”

WWW How We Know What’s Inside Earth Earth’s Interior WWW Paleomagnetism (ancient magnetic fields)

How We Know What’s Inside Earth Earth’s Interior Paleomagnetism (ancient magnetic fields) Example: Mid-Ocean Ridges Time 1 = Normal polarity Time 2 = Reverse polarity Time 3 = Normal polarity

How We Know What’s Inside Earth Earth’s Interior How We Know What’s Inside Earth Magnetism Magnetic anomalies are useful in finding buried magnetic objects > more magnetic   (+) anomaly > ore deposits, mafic rocks   (+) anomalies

How We Know What’s Inside Earth Earth’s Interior Magnetism Magnetic anomalies are useful in finding buried magnetic objects > less magnetic   (-) anomaly > basins, craters, salt domes   (-) anomalies

Earth’s Interior Earth’s Interior WWW Solid Fe-rich Inner Core, liquid Fe-rich Outer Core, and a silicate-rich mantle & crust

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)

WWW Earth’s Interior Crust The lithosphere includes two different types of silicate CRUST: > Continental crust – Thicker (35 km avg.) & less dense (more buoyant; higher) > Oceanic crust – Thinner (7 km avg.) & more dense (less buoyant, lower)

WWW 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

WWW 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

WWW Links in this Lecture Earth’s Interior > 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