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Home , Structure of Earth

Composition and Internal Structure of

Source: NASA

Density of Earth

„ = /Volume

„ What is the volume (or diameter) of the Earth?

„ How much does the Earth weigh?

Diameter of the Earth

7.2/360 = 787/C C=39,350 km (now 40,030 km) Diameter = 12,525 km (now 12,742 km)

Alexandria

7.2º light rays from sun

7.2º

Syene

1 Mass of the Earth Cavendish (1798) using Newton’s Laws

Force = mass × acceleration (Newton’s 2nd Law)

mEarth ×mbody F = mbody × g = G × r2 (Newton’s Law of Universal Gravitation)

G is universal gravitation constant (6.672 × 10-11 m3kg-1s-2) g is acceleration due to gravity on earth, measured by timing how long it takes a mass to fall in a vacuum (9.8 ms-2) Mass of Earth = 5.9742 × 1024 kg

Average Density of Earth

„ Diameter of the Earth = 12,742 km (7,920 miles ) „ Mass of the Earth = 5.974 ××101024 kg (13.15 ×10× 1024 lb) „ Density = 5.5 g/cm3

Earth is actually not a perfect sphere: it is slightly oblate (squished) being fatter across the equator ( 12756 km diameter) than at the North and South Poles (12714 km diameter)

Mean Atomic Wt of Planets

Anderson and Kovach (1967)EPSL

2 Internal structures of terrestrial planets

1. Drilling the Earth!

Well.. Only 1/3 of depth can be explored

2. Xenolith from Deep Earth () :“”

(play video clip >>)

3 3. Seismic Data

Analogy of Air/Water

Play Animation>>

Earth Interior

W. W. Norton

Seismic Data give strong evidence of Existence of Discrete Layers

Int.Int.--C06abC06ab

W. W. Norton

4 What about the deeper interior?

Int.Int.--C.10aC.10a

W. W. Norton

… another evidence of liquid outer core

Int.Int.--C.09C.09

W. W. Norton

Another layer? ->-> Yes, Inner Core!

5 Compositional Terms Physical Property Terms

(Butter!) (Liquid)

Inner Core

Outer Core Mantle (Liquid)

Crust

Chemical compositions

„ Crust ->-> from rocks near the surface „ Mantle ->-> from mantle xenolith „ Core ->-> from comparison with meteorite

6 Crust

1) – Thicker (~40 km) ––LowerLower Density – Mainly composed of comp’ n

2) – Thinner (~7km) – Higher Density – Mainly composed of comp’n

Mantle

„ : Rigid

„ (~100- (~100-400400 km): less Rigid Upper (butter(butter--oror waxwax--like,like, semimoltensemimolten)) Mantle „ (~400 -700 km) „ Lower Mesosphere (below ~700 km) Mantle

„ Compositional difference between Crust and Mantle is significant, but not as large as the difference with Core.

„ Two types of high P rocks ––EclogiteEclogite – Peridotite „ Which one is the dominant type in mantle? – Needs to satisfy seismic data – Needs to satisfy petrologic data „ Peridotite is the dominant rock type

7 Core Composition? How do we know? „ Outer Core ––FeFe + Ni – Lower Density (compared to Inner Core) – Liquid ( in mo tio n)

„ Inner Core ––FeFe + Ni – Higher Density – Solid

Clue comes from Meteorite!

„ It is believed that a certain type of meteorites has primordial chemical composition of the .

„ It is probably a valid assumption that the chemical composition of such meteorite is very similar to the composition of the Earth. „ Then, which element is enriched or depleted in the crust/mantle? „ Furthermore, what would be the composition of the Earth’s core?

8 /

In

Fe2O3: 30% NiO: 2.1% Zn: 0.05% Cr: 0. 4%

Major Core Constituents!

Important Terms „ Refractory elements – High condensation T – Ca, Al, U, Ti, REEs „ Volatile elements – LLdtiTow condensation T ––K,K, Rb „ Incompatible Elements ((KdKd<< 1) – LILE (Large Ion Lithophile Element) ƒ K, RbRb,, Ce,Ce, Sr,Sr, Ba – HFSE (High Strength Element) ƒ ZrZr,, Nb,Nb, Hf,Hf, REEs, Th,Th, U, Ta

What caused such layering?

““Rain--OutOut Model”

Need !! (for this process + plate tectonicstectonics))

9 Heat (Energy) Source #1: Bombardment 1. During the Early Stage of Solar System Formation 2. Primordial Process 3. Enough to melt the whole planet (Magma ) 4. Earth and other Planets were very Hot!

Heat (Energy) Source #2: Differentiation

„ Sinking of FeFe--NiNi fraction to the center of the Earth (and other Planets) release gravitational potential energy „ During the Early Stage of Solar System Formation „ Primordial Process

Heat (Energy) Source #3: Tidal Force „ When a body1 act on the gravity on body2, the gravitational field may not even on the body2 „ Distortion is commonly induced „ Internal Friction results in dissipation of its rotational kinetics into Heat

10 Heat (Energy) Source #4: Radioactive Decay

„ Spontaneous changes (decay) in atomic nuclei – Parent: an unstable radioactive isotope – Daughter: the isotopes resulting from the decay of a parent „ Provides important info to Geologists ––(1)(1) age dating – (2) heat budget calculation „ Still occurring

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