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Formation of Planets and Earth Structure

Big Bang Theory

•  ~14 Ga •  All matter in one point •  Exploded •  Expanding still

From work of Einstein and Hubble

Food for thought

What is the shape of our solar system?

A.  Spherical (3-D): the Sun is in the center, the planets orbit in spherical shells.

B.  Disc shaped (3-D): fat in the center, tapering to planar at the edges. Sun in the middle.

C.  Planar ellipse (oval) that is almost circular (2-D)

Top view Edge view

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Consider H2O and the planets. Which of the following is correct? A.  Earth is the only planet with H2O on the surface. B.  Most of Earth’s H2O is in the oceans. C.  H2O was not originally present when the Earth formed, and

was added to the Earth early in it’s history.

Nebular Theory and formation of solar systems •  Clouds of gas/matter contract under the force of gravity. •  Gasses (moslty H and He) compress into dense balls = Star

–  Heat by compression to > 1x106 K –  Fuse heavier elements –  Emit light and HEAT

•  Supernova = exploded star •  Repeat process

Crab Nebula

A super nova

Nebular Theory

Look at the shape of these galaxies (not nebulae, but pretend)

Draw nebular theory

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How a super nova becomes a solar system

Terrestrial vs. Gaseous Planets

Accretion of Terrestrial Planets

•  Mercury, Venus, Earth, Mars + Asteroid belt •  Close to sun - HOT during accretion

–  Only refractory compounds are solid

•  Solar wind blows light particles away –  Planets too small to retain light elements

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Accretion of Jovian Planets

•  Jupiter, Saturn, Uranus, Neptune (not Pluto) •  Retention and accumulation of volatile compounds

–  Condense in cooler region - volatile compounds are solid –  Big Planets can ‘hold’ light elements (H, He) during solar wind

Where does water on Earth come from?

70% of Earth is covered with water. Problem: no water in the region of space where Earth formed. So, the material Earth formed from shouldn’t have contained water.

Where does the water on Earth come from? Planetesimals from beyond the snow line (meteorites) added water to Earth! Note, comets were not a major source of Earth’s water. Heterogeneous Accretion: Some

meteorites that collided with Earth near the end of its formation had ~18 wt% H2O locked up in minerals - this is ‘structural water’, not free molecular water. So, Earth’s water has been added (1) during accretion, and (2) after formation

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Relationships between planets: Why do the Inner Planets have lower

mass than outer planets? A.  They have greater density B.  They formed in a region where the

solar wind was strong. C.  They formed in a region where

temperatures were cold.

Relationships between planets: Why do the Outer Planets have lower

density than inner planets? A.  They have greater mass B.  They formed in a region where the

solar wind was strong. C.  They formed in a region where

temperatures were cold.

Origin of Earth’s Water

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Origin of Earth’s Core, and Mantle

Origin of Earth’s Moon

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Origin of the Moon!

Then, let’s look at Earth’s Structure

Let’s watch a summary of what we know

Topography of the Earth: Why are oceans deep? This is a fundamental observation about the Earth that hints at it’s structure

Ocean crust Continental Crust

The Hypsometric

Curve

There is something fundamentally different between Ocean Crust and Continents!

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Draw Earth’s Structure���1. Composition layers ���2. Mechanical layers

Composition vs. Mechanical layers of the Earth

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Now we can understand hypsometric curve

•  Ocean floor is ‘deeper’ than continents because –  Ocean lithosphere is thinner than

continental lithosphere –  Oceanic lithosphere is denser

than continental lithosphere –  Thus, due to relative buoyancy

the oceanic lithosphere does not ride as high on the asthenosphere compared to the continental lithosphere.

•  This is the concept of isostacy…

Isostasy: •  concept of isostacy…

–  Continental lithosphere sinks deeper and rides higher than oceanic lithosphere due to it’s thickness and lower density.

–  In this picture the thick board represents the continental lithosphere.

–  The thinner boards represent the oceanic lithosphere.

–  Note, if you remove the top of a continent, it ‘bobs’ up above the oceanic lithosphere.

Buoyancy Model What will happen if the thickness

of the block (ZA) is increased? A.  The base of the block will

sink deeper. B.  The top of the block will rise

higher C.  Both A and B D.  Nothing will happen, the

position of the block will not change.

ZBZA

ZU

model

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Archimedes’ Principle

More Examples of Isostasy:

Thick ice sinks deeper and rides higher than thin ice

More Isostasy:

Glacial isostatic rebound

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Now we understand this graph!

Why are the oceans deep relative to the continental surfaces? A.  The ocean water weighs down on the oceanic crust, causing

it to sink into the mantle. B.  Ice at high latitude on the continents ‘lifts’ the low-latitudes

up like a teeter-totter. C.  The continental lithosphere is thicker than the oceanic

lithosphere. D.  The oceanic crust is thin, so it floats lower on the mantle

Review questions

1.  How does temperature vary across the solar system? 2.  How does planet size and density change with distance from the sun? 3.  What caused the variation in planet size and density?

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Review questions 1.  How did the Moon form? 2.  How does the Moon differ from the Earth (size, mass, density, structure)? 3.  When did the moon form?

Review questions 1.  What does the hypsometric curve tell us about the Earth? 2.  How is the continental lithosphere different from the oceanic lithosphere 3.  What does the lithosphere ‘float’ on?

Ocean Crust

Continental Crust

Review questions 1.  What are the four elements that compose 90% of the Earth? 2.  What are the composition layers of the Earth? 3.  Where is most of Earth’s water stored? 4.  Compare and contrast the Lithosphere and the Mantle. 5.  Compare and contrast the Lithosphere and the Asthenosphere. 6.  Compare and contrast the Lithosphere and the Crust. 7.  What is Isostacy and how does it explain elevated continents and deep oceans?