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Chapter 2 Chapter 2 OriginsOrigins

Formation of Universe, Solar Formation of Universe, Solar System and EarthSystem and EarthCreation of Creation of OceansOceans

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Formation of the UniverseFormation of the Universe

Big Bang, 13*10Big Bang, 13*1099 years ago years agoFormation of elementary particlesFormation of elementary particlesGravitational formation of dense Gravitational formation of dense

regionsregions1*101*1099 yrs later yrs laterfirst starsfirst stars

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The Big Bang Theory is the dominant scientific theory about the origin of the universe. According to the big bang, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions.

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Supporting Evidence for the Big Bang •Edwin Hubble discovered spreading of galaxies. •Cosmic background radiation (the glow left over from the explosion itself) discovered in 1964.

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Origin of a GalaxyOrigin of a Galaxy

Huge rotating aggregation of stars, dust, Huge rotating aggregation of stars, dust, gas and other debris held together by gas and other debris held together by gravity.gravity.

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Origin of the Solar SystemOrigin of the Solar System

Rotating cloud of gas from which sun Rotating cloud of gas from which sun and planets formedand planets formed

Initiated by “supernova” = exploding Initiated by “supernova” = exploding starstar

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Nuclear Fusion: The joining of atoms under tremendous temperatures and pressures to create atoms of a heavier element. In the Sun, four hydrogen atoms are fused to create each helium atom. Two of the hydrogen's protons become neutrons in the process

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Moderate Size Stars (Our Sun): C & O

Large Stars (more, H & He): Fe

Supernova: Heavier Elements Formed

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Origin of the Solar SystemOrigin of the Solar System

Rotating cloud of gas from which sun Rotating cloud of gas from which sun and planets formedand planets formed

Initiated by “supernova” = exploding Initiated by “supernova” = exploding starstar

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A nebula (a large, diffuse gas cloud of gas and dust) contracts under gravity. As it contracts, the nebula heats, flattens, and spins faster, becoming a spinning disk of dust and gas.

Star will be born in center.

Planets will form in disk.

Warm temperatures allow only metal/rock “seeds” to condense in the inner solar system.

Hydrogen and helium remain gaseous, but other materials can condense into solid “seeds” for building planets.

Cold temperatures allow “seeds” to contain abundant ice in outer solar system.

Terrestrial planets are built from metal and rock.

Solid “seeds” collide and stick together. Larger ones attract others with their gravity, growing bigger still.

The seeds of gas giant planets grow large enough to attract hydrogen and helium gas, making them into giant, mostly gaseous planets; moons form in disks of dust and gas that surround the planets.

Terrestrial planets remain in inner solar system.

Gas giant planets remain in outer solar system.

“Leftovers” from the formation process become asteroids (metal/rock) and comets (mostly ice).

Not to scale

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Early EarthEarly Earth

Accretion (Gaining material)Accretion (Gaining material)Differentiation (Separating based on Differentiation (Separating based on

density density density stratification) density stratification)Evidence of water- 3.9*10Evidence of water- 3.9*1099 yrs ago yrs ago

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The planet grew by the aggregation of particles. The planet grew by the aggregation of particles. Meteors and asteroids bombarded the surface, Meteors and asteroids bombarded the surface, heating the new planet and adding to its heating the new planet and adding to its growing mass. At the time, Earth was composed growing mass. At the time, Earth was composed of a homogeneous mixture of materials.of a homogeneous mixture of materials.

The result of density stratification: The result of density stratification: an inner and an inner and outer core, outer core,

a mantle, a mantle, and the crust.and the crust.

Earth lost volume because of gravitational Earth lost volume because of gravitational compression. High temperatures in the interior compression. High temperatures in the interior turned the inner Earth into a semisolid mass; turned the inner Earth into a semisolid mass; dense iron (red drops) fell toward the center to dense iron (red drops) fell toward the center to form the core, while less dense silicates move form the core, while less dense silicates move outward. Friction generated by this movement outward. Friction generated by this movement heated Earth even more.heated Earth even more.

Earth, Ocean and Atmosphere accumulated in layers sorted by density

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How did water and water vapor form on How did water and water vapor form on early Earth?early Earth?

The Sun stripped away Earth’s first atmosphereThe Sun stripped away Earth’s first atmosphere Gases, including water vapor, released by the Gases, including water vapor, released by the

process of outgassing, replaced the first process of outgassing, replaced the first atmosphere.atmosphere.

Water vapor in the atmosphere condensed into Water vapor in the atmosphere condensed into clouds.clouds.

After millions of years, the clouds cooled enough After millions of years, the clouds cooled enough for water droplets to form.for water droplets to form.

Hot rain fell and boiled back into the clouds.Hot rain fell and boiled back into the clouds. Eventually, the surface cooled enough for water Eventually, the surface cooled enough for water

to collect in basins.to collect in basins.

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Sources of WaterSources of Water

* Mantle rocksMantle rocksEvidence from meteoritesEvidence from meteoritesRelease through volcanic activityRelease through volcanic activity

* Outer spaceOuter spaceEvidence from Dynamics ExplorerEvidence from Dynamics Explorer

1515Fig. 2-11, p. 49

100Methane, ammonia

75Atmosphere

unknown50 Nitrogen

WaterCon

cent

ratio

n of

A

tmos

pher

ic G

ases

(%)

25Carbon dioxide Oxygen

04.5 4 3 2 1

Time (billions of years ago)

The evolution of our atmosphere

Early atmosphere quite different from today’s

initial rise of O2 2.7 b. y. ago – but conclusive evidence is from 2.3 b. y. ago

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Fossil of a bacteria-Fossil of a bacteria-like organism (with like organism (with an artist’s an artist’s reconstruction) that reconstruction) that photosynthesized photosynthesized and released oxygen and released oxygen into the atmosphere. into the atmosphere.

Among the oldest Among the oldest fossils ever fossils ever discovered, this discovered, this microscopic filament microscopic filament from northwestern from northwestern Australia is about Australia is about 3.5 billion years old.3.5 billion years old.

Life probably originated in the ocean

1717Fig. 2-15, p. 51

Billions of years ago13 Big bang

Billions of years ago

4.6 Earth forms

11 First galaxies form

4.2 Ocean forms Millions of years ago

3.8 Oldest dated rocks 8003.6 First evidence

of life

Solar nebula begins to form5.5 2 Oxygen

revolution begins

Millions of years ago 66

End of dinosaurs

First fishes appear

510

4.6 50 First marine mammals

Earth forms

0.8 Ocean and atmosphere

reach steady state (as today)

Pangaea breaks apart210

End of dinosaurs

Today 0 Today Today 66 Today 3 Humans appear Today

3.5

Sun's output too low for liquid-water ocean

5The sun swells, planets destroyed

Billions of years in the future

First animals arise

Age and Time – Age and Time – Past and FuturePast and Future

Future

Past

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Age and TimeAge and Time1 billion = 1,000,000,000 or 101 billion = 1,000,000,000 or 1099

Earth is 4.6 * 10Earth is 4.6 * 1099 years old years oldOceans are 4.2 * 10Oceans are 4.2 * 1099 years old years oldOldest rocks date from 3.8 * 10Oldest rocks date from 3.8 * 109 9 years agoyears agoFirst evidence of life dates from 3.6 * 10First evidence of life dates from 3.6 * 109 9

years ago years ago 1 million = 1,000,000 or 101 million = 1,000,000 or 1066

Ocean and atmosphere reach the state we Ocean and atmosphere reach the state we know today 800 * 10know today 800 * 106 6 years ago years ago

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Radioactive Decay SeriesRadioactive Decay Series

48.8 billion years Strontium-87 Rubidium-87

14.0 billion years Lead-208 Thorium-232

704 million years Lead-207 Uranium-235

4.5 billion years Lead-206 Uranium-238

Currently Accepted Half-Life Values Stable Daughter Product Parent Isotope

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The future of EarthHow long can Earth exist?

Our Sun will begin to die in 5 billion years.6 billion years from now the sun will enter the red giant phase and will engulf the inner planets.At that time, Earth will probably be recycled into component atoms.

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SummaryMost of the atoms that make up Earth, its ocean, and its inhabitants were formed within stars billions of years ago. Stars spend their lives changing hydrogen and helium into heavier elements. As they die, some stars eject the elements into space during cataclysmic explosions. The sun and planets, including Earth, condensed from a cloud of dust and gas enriched by the recycled remnants of exploded stars.

Earth formed by accretion – the clumping of small particles into a large mass. The mass heated as it grew and eventually melted. The heavy iron and nickel crashed toward Earth’s center to become its core; the lighter silicates and aluminum compounds rose to the surface to form a crust. Earth became density stratified – that is layered by density.

The ocean formed as soon as Earth was cool enough for water to remain liquid. Life followed soon thereafter.