Chapter 1 Cosmology and the Birth of Earth

1. Chapter 1 Cosmology and the Birth of Earth LECTURE OUTLINE earth Portrait of a Planet Third Edition ©2008 W. W. Norton & Company, Inc.

2. Cosmology and the Birth of Earth Prepared by Ron Parker, Earlham College, Department of Geosciences Richmond, Indiana

3. 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.

4. 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.

5. 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?

6. 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 +).

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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!!

16. 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

17. 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!

18. 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.

19. 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.

20. 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.

21. 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

22. 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.

23. 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.

24. 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.

25. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth The Modern Universe

26. 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.

27. 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.

28. 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).

29. 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.

30. 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).

31. 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.

32. 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.

33. 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.

34. 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.

35. 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.

36. 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.

37. 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.

38. 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.

39. 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.

40. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth Solar System Formation Synopsis

41. 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.

42. 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.