Earth’s InteriorEarth’s InteriorLet’s get to the heart of the EarthLet’s get to the heart of the Earth

By the Lunar and Planetary By the Lunar and Planetary InstituteInstitute

For use in teacher workshopsFor use in teacher workshops

Image credit: NASA

CompositionalCrustMantleCore

Physical / MechanicalLithosphere

AsthenosphereMesosphere Image credit: USGS

What We Know - CrustWhat We Know - Crust Two types of crust:Two types of crust:

ContinentalContinental 30% of crust30% of crust 40 Km thick40 Km thick Oldest is 3.8 billion Oldest is 3.8 billion

years (90% solar system years (90% solar system age; missing ~700 m.y.)age; missing ~700 m.y.)

Oceanic crustOceanic crust 5-10 Km thick5-10 Km thick 200 Ma oldest; 100 Ma 200 Ma oldest; 100 Ma

averageaverage

Image credit: USGS

What We Know - MantleWhat We Know - Mantle Density – between Density – between

crust and corecrust and core 3.3 - 5.5 g/cm3.3 - 5.5 g/cm33

Samples from Samples from volcanic volcanic eruptions, basalt eruptions, basalt composition; lab composition; lab experimentsexperiments

Image credit: John Lahr, USGS Open-File Report 99-132

What We Infer – CoreWhat We Infer – Core No direct No direct

samplessamples Probably heavy Probably heavy

stuffstuff Liquid outer Liquid outer

(molten iron), (molten iron), solid inner solid inner (iron, nickel)(iron, nickel)

Image credit: John Lahr, USGS Open-File Report 99-132

What We Infer – CoreWhat We Infer – Core Total density of Earth is Total density of Earth is

~5,500 km/g~5,500 km/g33

Avg. surface density is ~3,000 Avg. surface density is ~3,000 km/gkm/g33

Core must be very dense!Core must be very dense! Why iron? Meteorites!Why iron? Meteorites!

Earth’s InteriorEarth’s Interior How do we infer the properties of How do we infer the properties of

the core?the core?

Seismic WavesSeismic Waves

Earthquakes generate three types of waves – P, S, & surface waves

We will just concern ourselves with P & S waves

Image credit: USGS

Wave TypesWave Types

Transverse (S) Transverse (S) Waves – particles Waves – particles move move perpendicular to perpendicular to direction of direction of disturbance; rock is disturbance; rock is moved (sheared)moved (sheared)

Image credit: USGS

Wave TypesWave Types Longitudinal (P) Longitudinal (P)

Waves – push-pull Waves – push-pull waves; particles waves; particles move parallel to move parallel to direction of direction of disturbance; rock disturbance; rock changes volume changes volume (compressed & (compressed & dilated) dilated) Image credit: USGS

Earthquake WavesEarthquake Waves P-waves (longitudinal) travel through P-waves (longitudinal) travel through

liquids & solidsliquids & solids

S-waves (transverse) do NOT travel S-waves (transverse) do NOT travel through liquids; solids onlythrough liquids; solids only

Earthquake Waves Hint at Internal Earthquake Waves Hint at Internal LayeringLayering

P-waves (longitudinal) are able to travel through liquids (outer core)

S-waves (transverse) are NOT able to travel through liquids (outer core)

Image credit: LPI

WebsitesWebsites Earthquake dataEarthquake data http://www.iris.edu/hq/

TERC’s Exploring EarthFANTASTIC interactive lessons for students about Earth, visualizations, and more. In particular, explore how we have modeled Earth’s internal structure using seismic waves http://www.classzone.com/books/earth_science/terc/content/investigations/es0402/es0402page04.cfm?chapter_no=investigation