Earth’s Interior
Let’s get to the heart of the Earth
By the Lunar and Planetary
Institute
For use in teacher workshops
Image credit: NASA
Compositional
Crust
Mantle
Core
Image credit: USGS
Physical / Mechanical
Lithosphere
Asthenosphere
Mesosphere
What We Know - Crust
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Two types of crust:

Continental
30% of crust
 40 Km thick
 Oldest is 3.8 billion years (90%
solar system age; missing ~700
m.y.)

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Oceanic crust
5-10 Km thick
 200 Ma oldest; 100 Ma average

Image credit: USGS
What We Know - Mantle


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Density – between
crust and core
3.3 - 5.5 g/cm3
Samples from volcanic
eruptions, basalt
composition; lab
experiments
Image credit: John Lahr, USGS Open-File Report 99-132
What We Infer – Core


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No direct samples
Probably heavy stuff
Liquid outer
(molten iron), solid
inner (iron, nickel)
Image credit: John Lahr, USGS Open-File Report 99-132
What We Infer – Core

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Total density of Earth is ~5,500 km/g3
Avg. surface density is ~3,000 km/g3
Core must be very dense!
Why iron? Meteorites!
Earth’s Interior

How do we infer the properties of the core?
Seismic Waves
Earthquakes generate
three types of waves –
P, S, & surface waves
We will just concern
ourselves with P & S
waves
Image credit: USGS
Wave Types

Transverse (S) Waves –
particles move
perpendicular to direction
of disturbance; rock is
moved (sheared)
Image credit: USGS
Wave Types

Longitudinal (P) Waves
– push-pull waves;
particles move parallel to
direction of disturbance;
rock changes volume
(compressed & dilated)
Image credit: USGS
Earthquake Waves

P-waves (longitudinal) travel through liquids & solids

S-waves (transverse) do NOT travel through liquids;
solids only
Earthquake Waves Hint at Internal Layering


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
Websites
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Earthquake data
http://www.iris.edu/hq/
TERC’s Exploring Earth
FANTASTIC 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/investigation
s/es0402/es0402page04.cfm?chapter_no=investigation