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Earth: Portrait of a Planet, 3rd edition Chapter 1 Cosmology and the Birth of Earth 2008, by Stephen Marshak © W. W. Norton & Company Our Island in Space We pass our lives on our one planet Earth. Earth may seem endless; it isn’ ’t. isn isn’t. Viewed from space, Earth is a small, shiny globe. It is truly our island oasis in space. Cosmology and the Birth of Earth 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. ever ever-changing. It has a long and complex history. 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? Cosmology Study of the structure and evolution of the Universe. Cosmology is a complicated science. Cosmology These ideas are often culturally determined. Commonly include supernatural forces. Requires thinking in unfamiliar scales of space and time. Spatial scales. Ideas about the Universe have a rich history. The Western tradition applies scientific discovery. 21 meters), to DAttometers (10--21 D10s of billions of light years (9.4622 meters +). Temporal scales. 21 seconds), to DAttoseconds (10--21 D10s of billions of years (3.1517 seconds +). PowerPoint slides prepared by Ronald L. Parker Earlham College, Department of Geosciences Richmond, Indiana [email protected] 1 Earth: Portrait of a Planet, 3rd edition Chapter 1 Cosmology and the Birth of Earth 2008, by Stephen Marshak © W. W. Norton & Company 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. Earth ’s Changing Place Earth’s 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. (100 (100-170 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. Sir Isaac Newton (1642-1727) devised… (1642 (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. PowerPoint slides prepared by Ronald L. Parker Earlham College, Department of Geosciences Richmond, Indiana [email protected] Movement in the heavens was attributed to deities. The Renaissance A rebirth of rational thinking in 15th--century 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. didn didn’t Planetary orbits weren’ ’t circular. weren weren’t Not all bodies orbited Earth. The Enlightenment 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. 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. 2 Earth: Portrait of a Planet, 3rd edition Chapter 1 Cosmology and the Birth of Earth 2008, by Stephen Marshak © W. W. Norton & Company Earth ’s Rotation Earth’s How do we know that Earth rotates about Polaris? Clearly visible in a time-lapse photograph of the night sky. time time-lapse Foucault’ ’s pendulum (1851) proved Earth’ ’s rotation. Foucault Earth Foucault’s Earth’s Earth ’s Circumference Earth’s Eratosthenes calculated ~25,000 miles in ~ 200 B.C.E. 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’ Earth’s Earth’s circumference. He was correct!! Distances from Earth The dimensions of the Universe are staggering! We must consider huge expanses of space and time. 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. The speed of light (c c) is 186,000 miles/s (300,000 km/s). ((c) 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 end of visible Universe is > 13 billion light years away You are HERE! Modern View of the Universe Current concepts differ wildly from 100 years ago. Questions The vastness of the Universe is almost incomprehensible. Andromeda, the next galaxy, is 2,500,000 light years away. 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. The Universe contains more than a billion galaxies. PowerPoint slides prepared by Ronald L. Parker Earlham College, Department of Geosciences Richmond, Indiana [email protected] 3 Earth: Portrait of a Planet, 3rd edition Chapter 1 Cosmology and the Birth of Earth 2008, by Stephen Marshak © W. W. Norton & Company The Doppler Effect Waves compress or relax with relative motion. Applies to waves of both sound and light. The Doppler Effect 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). lower). This is commonly heard as cars whiz by on a road. Visible wavelengths range from 400 to 700 nanometers. 400 nm – Blue = Higher frequency 700 nm – Red = Lower frequency The Doppler Effect The Expanding Universe A moving star displays DopplerDoppler-shifted Doppler-shifted light. Light from an approaching star is compressed. This causes a shift to higher frequencies, so that… 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. Light waves behave like sound waves. Visible light is electromagnetic radiation. Light from distant galaxies appeared ““red red shifted.” 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. 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. The Modern Universe PowerPoint slides prepared by Ronald L. Parker Earlham College, Department of Geosciences Richmond, Indiana [email protected] 4 Earth: Portrait of a Planet, 3rd edition Chapter 1 Cosmology and the Birth of Earth 2008, by Stephen Marshak © W. W. Norton & Company 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. nucleosynthesis. The Universe continued to… to… After the Big Bang 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… in… Temperature. Density. Rate of rotation. Expand. Cool. Decrease in density. After the Big Bang Condensed nebulae formed flattened accretion discs. Heat and mass from collapse ignited nuclear fusion. generation stars consumed H2 fuel rapidly. These 1st--generation As the stars became H2 starved, they initiated… initiated… With expansion and cooling, atoms began to bond. Nucleosynthesis Stars are truly ““element element factories.” factories.” Big bang nucleosynthesis formed lighter elements. Heavier elements are from stellar nucleosynthesis. nucleosynthesis. Elements with atomic #s > 26 form during supernovae. Collapse and heating. Heavy element production. Catastrophic explosion (supernova). Atomic #s 1, 2, 3, 4 and 5 (H, He, Li, Be, and B). Atomic #s 6 - 26 (C to Fe). Nucleosynthesis The mass of a star governs its element production. Smaller-mass stars (like the Sun). Smaller Smaller-mass ““Burn” Burn” Burn” slowly. Live longer (10 Ga). Ga). Create lighter elements up to carbon (C). 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. Larger-mass stars (10-100x the mass of the Sun). Larger (10 Larger-mass (10-100x ““Burn” Burn” Burn” rapidly. Are shorter lived (10s of Ma). Create heavier elements up to iron (Fe). PowerPoint slides prepared by Ronald L. Parker Earlham College, Department of Geosciences Richmond, Indiana [email protected] 5 Earth: Portrait of a Planet, 3rd edition Chapter 1 Cosmology and the Birth of Earth 2008, by Stephen Marshak © W. W. Norton & Company The Solar System The Planets: An Overview Two groups of planets occur in the solar system. Terrestrial (Earth-like) - Small, dense, rocky planets. (Earth (Earth-like) Mercury, Venus, Earth, and Mars. Jovian (Jupiter-like) - Large, low-density, gas-giant planets. (Jupiter low gas (Jupiter-like) low-density, gas-giant Jupiter, Saturn, Uranus, and Neptune. Earth shares the solar system with 7 other planets. Planet – A precise definition developed in 2006. A planet… 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. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak The Solar System Our solar system also includes… includes… The Sun – An average star. Asteroids – Rocky or metallic fragments. Comets – Fragments of ice orbiting the Sun. Kuiper Belt and Oort Belt objects. 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. Planetary systems have been found near other stars. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak 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. Chapter 2: Journey to the Center of the Earth Particles coalesce to form planetesimals. Chapter 2: Journey to the Center of the Earth Solar System Formation Planetesimals accumulate into a larger mass. An irregularly-shaped protoirregularly-shaped irregularly proto-Earth 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. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth PowerPoint slides prepared by Ronald L. Parker Earlham College, Department of Geosciences Richmond, Indiana [email protected] Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth 6 Earth: Portrait of a Planet, 3rd edition Chapter 1 Cosmology and the Birth of Earth 2008, by Stephen Marshak © W. W. Norton & Company Solar System Formation Soon, a small planetoid collides with Earth. Debris forms a ring around the Earth. The debris coalesces and forms the Moon. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the 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. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the 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° 3° of the Sun's equator. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 2: Journey to the Center of the Earth PowerPoint slides prepared by Ronald L. Parker Earlham College, Department of Geosciences Richmond, Indiana [email protected] 7
