Origin, Evolution

& Composition of the Earth

GS117 Lecture 2

January 10, 2000

C. Lithgow-Bertelloni

Excellent Lecture Notes on Solar System Evolution

Outline Origin & Evolution

o Earth's Place in the Solar System

o Our Universe o Beginning and Evolution of

the Universe The Big Bang

Cosmic Background Radiation

Inhomogeneity Birth of Stars Origin of Planets

o How did the Earth Form? Origin of the Solar

System Origin of the planets

o How did the Earth Grow & Differentiate? 

Bombardment  Insulation  Gravitational

Compression Radioactive Decay

o Present-Day Earth Structure of the Earth

o Chemical Layering Crust

Continental Oceanic

Mantle Core

o Mechanical Lithosphere Mantle Outer Core Inner Core

Plate Tectonics Primer o Definition

o Plate Boundaries

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Our Earth

Earth in the Solar System  

Density of terrestrial planets: 4.0-5.5 g/cm3 Density of outer planets: 0.6-1.7 g/cm3

Mass Distribution:

Sun 99.86% (1) Planets 0.135 % (9)

Satellites 0.004 % (32)

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Our Universe

From the Hubble Deep Field Experiment

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Beginning & Evolution

of the Universe

Thompson & Turk, 1999

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The Big Bang

Introduction to Cosmology

Cosmic Bacgkround Radiation

Uniform

Learn about the Big Bang & Cosmic Background Radiation COBE Educational Resources

The Big Bang

Cosmic Bacgkround Radiation

Inhomogeneity

 From NASA's DMR Experiment

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Birth of Stars

Dense Molecular Clouds

Birth and Death of StarsNext Slide

The Origin of Planets

Circumstellar Disks

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How did the Earth Form

Formation of the Solar System

Condensation from rotating cloud of dust (nebula)

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How did the Earth Grow

& Differentiate?

Planetary Formation

I. Bombardment

II. Insulation                                                = HOT START

III. Gravitational Compression

(IV. Radioactive Decay)

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Present-Day Earth I. Hot Start-Melting

II. Migration of dense material to center

III. Differentiated Earth

IV. Present-Day Earth is Still Hot: Why?

o Heat from bombardment and accretion still needs to be released-this is called PRIMORDIAL HEAT and is one of the two main sources of heat in the Earth's interior

o Radioactive Elements are still decaying and releasing energy, this is the second main source of heat in the Earth's interior-RADIOACTIVE DECAY of Th, U, K

V.Will it stay hot forever? NO!- It's been cooling down since its origin (4.5-4.6 billion years ago)

VI. How does it lose its heat?-Through Plate Tectonics

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Structure of the Earth

Interior of the Earth is layered (i.e. DIFFERENTIATED)-total radius 6371 km

Chemical Differentiation [Layers of different Chemical Composition]

o crust - two types: continental (0-70 km thick; ave 35 km), oceanic (0-20 km thick; ave 6-8 km)

o mantle- from (6-35 km depth to 2891 km depth) o core-Made of iron (from 2891 km depth to the center

6371 km) outer part liquid (2891 km to 5120 km) inner part solid (5120 km to 6371 km)

Mechanical Differentiation [Layers that react differently when you try to deform them]

o Lithosphere [Crust (oceanic or continental) + 70-100 km of coldest Mantle]-

COLD BRITTLE (BREAKS INTO BIG PIECES [TECTONIC PLATES]-and

gives rise to EARTHQUAKE & VOLCANIC ACTIVITY) o Rest of Mantle-

WARM

PLASTIC Flows and this flow drives plate tectonics

o Core- HOT LIQUID Moves as fast as ocean currents. Generates the Earth's

magnetic field

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Plate Tectonics Primer

This is how the geosphere loses its heat and how it expresses its dynamic nature

Plate Tectonics : the upper mechanical layer of the Earth (lithosphere) is broken into several rigid pieces, which we call plates, that move with respect to one another throughout the course of earth’s history. All

deformation occurs at the boundaries between plates. Explains distribution of earthquakes, volcanoes, mountains, rock types, etc. There are

three types of plate boundaries.

Three boundaries (all deformation occurs)

Divergent (material is created)-plates move away from each other

Convergent (material is consumed)- plates move towards each other

Transform (no creation, no consumption; plates slide past each other)- plates slide past each other