Chapter 1 Cosmology and the Birth of Earth

Chapter 1 Cosmology and the Birth of Earth LECTURE OUTLINE earth Portrait of a Planet Third Edition © 2008 W. W. Norton & Company, Inc. Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

Prepared by Ron Parker, Cosmology and the Birth of Earth Earlham College, Department of Geosciences

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. < Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: 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. = It has a long and complex history. Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

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? Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

Cosmology Study of the structure and evolution of the Universe. < Cosmology is a complicated science. < = Requires thinking in unfamiliar scales of space and time. 4 Spatial scales. a. Attometers (10 -21 meters), to a 10 s of billions of light years (9. 4622 meters +). 4 Temporal scales. a. Attoseconds (10 -21 seconds), to a 10 s of billions of years (3. 1517 seconds +). Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

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

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: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

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

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

The Renaissance < A rebirth of rational thinking in 15 th-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: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

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

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

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

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. 2 o. He calculated that 800 km was 1/50 th of Earth’s circumference. < He was correct!! < Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

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). 4 The Moon is 1. 3 light seconds (~237, 000 miles) away. 4 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 Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

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! Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

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

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

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. 4 Anna hears a higher pitch from compressed sound waves. 4 Bill hears a lower pitch from expanded sound waves. 4 As the train passed Anna, the pitch would drop (higher to lower). 4 This is commonly heard as cars whiz by on a road. Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

The Doppler Effect Light waves behave like sound waves. < Visible light is electromagnetic radiation. < = Visible wavelengths range from 400 to 700 nanometers. 4400 nm – Blue = Higher frequency 4700 nm – Red = Lower frequency Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

The Doppler Effect < A moving star displays Doppler-shifted light. = Light from an approaching star is compressed. 4 This causes a shift to higher frequencies, so that… 4 Stars moving toward Earth are shifted toward blue. = Light from a receding star is expanded. 4 This causes a shift to lower frequencies, so that. . . 4 Stars moving away from Earth are shifted toward red. Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

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

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

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

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… 4 Expand. 4 Cool. 4 Decrease in density. Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

After the Big Bang < With expansion and cooling, atoms began to bond. = Hydrogen formed H 2 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. Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

After the Big Bang Condensed nebulae formed flattened accretion discs. < Heat and mass from collapse ignited nuclear fusion. < These 1 st-generation stars consumed H 2 fuel rapidly. < As the stars became H 2 starved, they initiated… < = Collapse and heating. = Heavy element production. = Catastrophic explosion (supernova). Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

Nucleosynthesis Stars are truly “element factories. ” < Big bang 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. Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

Nucleosynthesis < The mass of a star governs its element production. = Smaller-mass stars (like the Sun). 4“Burn” slowly. 4 Live longer (10 Ga). 4 Create lighter elements up to carbon (C). = Larger-mass stars (10 -100 x the mass of the Sun). 4“Burn” rapidly. 4 Are shorter lived (10 s of Ma). 4 Create heavier elements up to iron (Fe). Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

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. Earth: Portrait of a Planet, 3 rd 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… 4 Is a large solid body orbiting a star (e. g. , the Sun). 4 Has a nearly spherical shape. 4 Has cleared its neighborhood of other objects. 4 Thus, Pluto, previously defined as a planet, is excluded. = Moon – A solid body locked in orbit around a planet. Earth: Portrait of a Planet, 3 rd 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. 4 Mercury, Venus, Earth, and Mars. = Jovian (Jupiter-like) - Large, low-density, gas-giant planets. 4 Jupiter, Saturn, Uranus, and Neptune. Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

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

Solar System Formation The Nebular Theory < A 3 rd, 4 th 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. Earth: Portrait of a Planet, 3 rd 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. Earth: Portrait of a Planet, 3 rd 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. Earth: Portrait of a Planet, 3 rd 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. Earth: Portrait of a Planet, 3 rd 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. Earth: Portrait of a Planet, 3 rd edition, by Stephen Marshak Chapter 1: Cosmology and the Birth of Earth

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

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