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Chapter 1 Cosmology and the Birth of Earth. LECTURE OUTLINE. earth. Portrait of a Planet Third Edition. ©2008 W. W. Norton & Company, Inc. Cosmology and the Birth of Earth. Prepared by Ron Parker, Earlham College, Department of Geosciences Richmond, Indiana. Our Island in Space.

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Chapter 1 Cosmology and the Birth of Earth

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Chapter 1

Cosmology and the Birth of Earth

LECTURE OUTLINE

earth

Portrait of a Planet

Third Edition

©2008 W. W. Norton & Company, Inc.


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Cosmology and the Birth of Earth

Prepared by

Ron Parker,

Earlham College, Department of Geosciences

Richmond, Indiana


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Our Island in Space

  • We pass our lives on our one planet Earth.

  • Earth may seem endless; it isn’t.

  • Viewed from space, Earth is a small, shiny globe.

  • It is truly our island oasis in space.


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Our Island in Space

  • The Earth is a very special and unique planet.

    • Its temperature, composition and atmosphere favor life.

    • It is dynamic and ever-changing.

    • It has a long and complex history.


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Cosmology

  • Conscious thought distinguishes humans.

    • Developed across thousands of generations.

    • Lends us curiosity, insight, and the ability to learn.

  • As a result, we seek to explain our surroundings.

    • Where do we come from?

    • Where do we fit in the Universe?

    • Why are we here?


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Cosmology

  • Study of the structure and evolution of the Universe.

  • Cosmology is a complicated science.

    • Requires thinking in unfamiliar scales of space and time.

      • Spatial scales.

        • Attometers (10-21 meters), to

        • 10s of billions of light years (9.4622 meters +).

      • Temporal scales.

        • Attoseconds (10-21 seconds), to

        • 10s of billions of years (3.1517 seconds +).


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Cosmology

  • Ideas about the Universe have a rich history.

    • These ideas are often culturally determined.

    • Commonly include supernatural forces.

  • The Western tradition applies scientific discovery.


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Science

  • The systematic analysis of natural phenomenon.

  • Has evolved as the most significant human development for understanding the natural world.

  • Rationally explains cosmological evolution.

  • Scientific understanding can evolve and change.


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Earth’s Changing Place

  • 3,000 years ago, humans knew the heavens well.

    • They knew that stars were fixed relative to other stars.

    • They knew that stars moved predictably across the sky.

    • They saw retrograde motion separating planets from stars.

    • They did not think of Earth as a planet, however.

  • Movement in the heavens was attributed to deities.


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An Evolving Image of Earth

  • The ancients thought the Universe was geocentric.

    • Heavenly bodies circle around a motionless central Earth.

    • Proven by Ptolemy (100-170 C.E.), the idea was still wrong.

    • Yet it held as doctrine for 1,400 years during the dark ages.

    • It became religious dogma supporting the importance of Earth in the scheme of heaven.


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The Renaissance

  • A rebirth of rational thinking in 15th-century Europe.

    • Copernicus – Published evidence for heliocentricity.

    • Kepler – His elliptical planetary orbits refuted Ptolemy.

    • Galileo – Observed moons orbiting Jupiter.

  • These ideas were considered to be heresy.

    • Earth didn’t center the Universe.

    • Planetary orbits weren’t circular.

    • Not all bodies orbited Earth.


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The Enlightenment

  • Sir Isaac Newton (1642-1727) devised…

    • The Law of Universal Gravitation.

    • The Three Laws of Motion.

    • The mathematics of change (calculus).

  • He proved that natural law governs natural events.

  • Geocentricity faded away.


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Earth as a Sphere

  • A flat Earth was dispelled by ~ 250 B.C.E.

  • Abundant evidence suggested a spherical Earth.

    • A curved shadow crossed the Moon during eclipses.

    • Only the tops of distant sailing ships were visible.

  • In 1520, Magellan circumnavigated this sphere.


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Earth’s Rotation

  • How do we know that Earth rotates about Polaris?

    • Clearly visible in a time-lapse photograph of the night sky.

    • Foucault’s pendulum (1851) proved Earth’s rotation.


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Earth’s Circumference

  • Eratosthenes calculated ~25,000 miles in ~ 200 B.C.

  • He measured shadows in deep wells 800 km apart.

    • Measurement taken at noon on the same day.

    • Syene – Shadow absent (directly overhead).

    • Alexandria – Shadow at 7.2o.

  • He calculated that 800 km was

    1/50th of Earth’s circumference.

  • He was correct!!


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Distances from Earth

  • The dimensions of the Universe are staggering!

  • We must consider huge expanses of space and time.

    • The speed of light (c) is 186,000 miles/s (300,000 km/s).

      • The Moon is 1.3 light seconds (~237,000 miles) away.

      • The Sun is 8.3 light minutes (~93 million miles) away.

    • A light year measures a distance of 5.87 trillion miles.

    • Alpha Centauri, the closest star, is 4.3 light years away.

    • The visible Universe is > 13 billion light years away


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Modern View of the Universe

  • Current concepts differ wildly from 100 years ago.

    • Earth is one of nine planets in the solar system.

    • The solar system is on an arm of the Milky Way galaxy.

    • Our Sun is one of 300 billion stars in this galaxy.

You are HERE!


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Modern View of the Universe

  • Current concepts differ wildly from 100 years ago.

    • The vastness of the Universe is almost incomprehensible.

    • Andromeda, the next galaxy, is 2,200,000 light years away.

    • The Universe contains more than a billion galaxies.


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Questions

  • Science is the basis for addressing hard questions.

    • How did the Universe form?

    • Do galaxies move with respect to each other?

    • Is the Universe expanding? Contracting?

    • How do we know anything about these matters?

  • The Doppler Effect permits us to detect star motion.


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The Doppler Effect

  • Waves compress or relax with relative motion.

  • Applies to waves of both sound and light.

    • The stopped train sounds the same to Anna and Bill.

    • The moving train sounds different to Anna and Bill.

      • Anna hears a higher pitch from compressed sound waves.

      • Bill hears a lower pitch from expanded sound waves.

      • As the train passed Anna, the pitch would drop (higher to lower).

      • This is commonly heard as cars whiz by on a road.


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The Doppler Effect

  • Light waves behave like sound waves.

  • Visible light is electromagnetic radiation.

    • Visible wavelengths range from 400 to 700 nanometers.

      • 400 nm – Blue = Higher frequency

      • 700 nm – Red = Lower frequency


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The Doppler Effect

  • A moving star displays Doppler-shifted light.

    • Light from an approaching star is compressed.

      • This causes a shift to higher frequencies, so that…

      • Stars moving toward Earth are shifted toward blue.

    • Light from a receding star is expanded.

      • This causes a shift to lower frequencies, so that...

      • Stars moving away from Earth are shifted toward red.


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The Expanding Universe

  • Light from distant galaxies appeared “red shifted.”

  • In 1929, Hubble recognized this as a Doppler shift.

    • He concluded that galaxies were moving away rapidly.

    • No galaxies were found to be moving toward Earth.

  • This led to the development of the Expanding Universe Theory, analogous to expanding bread.


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Big Bang

  • When did the expanding Universe begin?

    • The best answer so far? The big bang.

    • All of the mass and energy in the Universe was packed into a single small point.

    • It exploded 13.7 Ga and has been expanding ever since.


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Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 1: Cosmology and the Birth of Earth

The Modern Universe


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Big Bang

  • Rooted in the Laws of Physics.

  • Started as a rapid cascade of events.

    • Protons and neutrons formed within 1 second.

    • Hydrogen atoms formed within 3 minutes.

    • Hydrogen fused to form new light elements (He, Be, Li, B) via big bang nucleosynthesis.

    • The Universe continued to…

      • Expand.

      • Cool.

      • Decrease in density.


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After the Big Bang

  • With expansion and cooling, atoms began to bond.

    • Hydrogen formed H2 molecules - The fuel of stars.

    • Atoms and molecules coalesced into gaseous nebulae.

  • Gravity caused collapse of gaseous nebulae.

  • Collapse resulted in increases in…

    • Temperature.

    • Density.

    • Rate of rotation.


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After the Big Bang

  • Condensed nebulae formed flattened accretion discs.

  • Heat and mass from collapse ignited nuclear fusion.

  • These 1st-generation stars consumed H2 fuel rapidly.

  • As the stars became H2 starved, they initiated…

    • Collapse and heating.

    • Heavy element production.

    • Catastrophic explosion

      (supernova).


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Nucleosynthesis

  • Stars are truly “element factories.”

  • Bigbang nucleosynthesis formed lighter elements.

    • Atomic #s 1, 2, 3, 4 and 5 (H, He, Li, Be, and B).

  • Heavier elements are from stellar nucleosynthesis.

    • Atomic #s 6 - 26 (C to Fe).

  • Elements with atomic #s > 26

    form during supernovae.


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Nucleosynthesis

  • The mass of a star governs its element production.

    • Smaller-mass stars (like the Sun).

      • “Burn” slowly.

      • Live longer (10 Ga).

      • Create lighter elements up to carbon (C).

    • Larger-mass stars (10-100x the mass of the Sun).

      • “Burn” rapidly.

      • Are shorter lived (10s of Ma).

      • Create heavier elements up to iron (Fe).


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Nucleosynthesis

  • When fuel dwindles, stars heat by inward collapse.

  • This leads to a cataclysmic explosion (a supernova).

  • The supernova creates heavier elements.

    • Uranium (atomic # 92) is the heaviest natural element.


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Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 1: Cosmology and the Birth of Earth

The Solar System

  • Earth shares the solar system with 7 other planets.

    • Planet – A precise definition developed in 2006. A planet…

      • Is a large solid body orbiting a star (e.g., the Sun).

      • Has a nearly spherical shape.

      • Has cleared its neighborhood of other objects.

      • Thus, Pluto, previously defined as a planet, is excluded.

    • Moon – A solid body locked in orbit around a planet.


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Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 1: Cosmology and the Birth of Earth

The Planets: An Overview

  • Two groups of planets occur in the solar system.

    • Terrestrial (Earth-like) - Small, dense, rocky planets.

      • Mercury, Venus, Earth, and Mars.

    • Jovian (Jupiter-like) - Large, low-density, gas-giant planets.

      • Jupiter, Saturn, Uranus, and Neptune.


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The Solar System

  • Our solar system also includes…

    • The Sun – An average star.

    • Asteroids – Rocky or metallic fragments.

    • Comets – Fragments of ice orbiting the Sun.

    • Kuiper Belt and Oort Belt objects.

  • Planetary systems have been found near other stars.


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Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 1: Cosmology and the Birth of Earth

Solar System Formation

The Nebular Theory

  • A 3rd, 4th or nth generation nebula forms 4.56 Ga.

    • Hydrogen and helium left over from the big bang.

    • Heavier elements produced by stellar fusion and supernovae.

  • The nebula condenses into an accretion disc.


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Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 1: Cosmology and the Birth of Earth

Solar System Formation

  • The ball at the center grows dense and hot.

  • Fusion reactions begin; the Sun is born.

  • Dust in the rings condenses into particles.

  • Particles coalesce to form planetesimals.


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Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 1: Cosmology and the Birth of Earth

Solar System Formation

  • Planetesimals accumulate into a larger mass.

  • An irregularly-shaped proto-Earth develops.

  • The interior heats and becomes soft.

  • Gravity shapes the Earth into a sphere.

  • The interior differentiates into…

    • a nickel-iron core, and

    • a stony (silicate) mantle.


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Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 1: Cosmology and the Birth of Earth

Solar System Formation

  • Soon, a small planetoid collides with Earth.

  • Debris forms a ring around the Earth.

  • The debris coalesces and forms the Moon.


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Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 1: Cosmology and the Birth of Earth

Solar System Formation

  • The atmosphere develops from volcanic gases.

  • When the Earth becomes cool enough,

    • moisture condenses and accumulates, and

    • the oceans are born.


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Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 1: Cosmology and the Birth of Earth

Solar System Formation

Synopsis


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Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 1: Cosmology and the Birth of Earth

Solar System Formation

  • The Nebular Theory of Solar System Formation is supported by the configuration of planets.

    • The orbital planes of the planets lie within 3° of the Sun's equator.


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This concludes the

Chapter 1

Cosmology and the Birth of Earth

LECTURE OUTLINE

earth

Portrait of a Planet

Third Edition

©2008 W. W. Norton & Company, Inc.


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