Unformatted text preview: Chapter 2 Origins
Formation of Universe, Solar System and Earth Creation of Oceans Origin of a Galaxy 1 Huge rotating aggregation of stars, dust, gas and other debris held together by 4 gravity. Formation of the Universe
Big Bang, 13*109 years ago Formation of elementary particles Gravitational formation of dense regions 1*109 yrs later first stars Origin of the Solar System
Rotating cloud of gas from which sun and planets formed Initiated by "supernova" = exploding star supernova" 2 5 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
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.
3 6 1 Moderate Size Stars (Our Sun): C & O Large Stars (more, H & He): Fe Supernova: Heavier Elements Formed Earth, Ocean and Atmosphere accumulated in layers sorted by density
The planet grew by the aggregation of particles. Meteors and asteroids bombarded the surface, heating the new planet and adding to its growing mass. At the time, Earth was composed of a homogeneous mixture of materials. Earth lost volume because of gravitational compression. High temperatures in the interior turned the inner Earth into a semisolid mass; dense iron (red drops) fell toward the center to form the core, while less dense silicates move outward. Friction generated by this movement heated Earth even more. The result of density stratification: an inner and outer core, a mantle,
7 and the crust. 10 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. Hydrogen and helium remain gaseous, but other materials can condense into solid "seeds" for building planets. Solid "seeds" collide and stick together. Larger ones attract others with their gravity, growing bigger still. Condensation Theory
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. Cold temperatures allow "seeds" to contain abundant ice in outer solar The seeds of system. Terrestrial planets are built from metal and rock. How did water and water vapor form on early Earth?
The Sun stripped away Earth's first atmosphere Earth' Gases, including water vapor, released by the process of outgassing, replaced the first outgassing, atmosphere. Water vapor in the atmosphere condensed into clouds. After millions of years, the clouds cooled enough for water droplets to form. Hot rain fell and boiled back into the clouds. Eventually, the surface cooled enough for water to collect in basins. 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). 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. Not to scale 8 11 Early Earth
Accretion (Gaining material) Differentiation (Separating based on density density stratification) stratification) Evidence of water- 3.9*109 yrs ago water- Sources of Water
* Mantle rocks Evidence from meteorites Release through volcanic activity * Outer space Evidence from Dynamics Explorer 9 12 2 The evolution of our atmosphere
100 Concentration of Atmospheric Gases (%) Methane, ammonia
initial rise of O2 2.7 b. y. ago but conclusive evidence is from 2.3 b. y. ago Age and Time
1 billion = 1,000,000,000 or 109 Earth is 4.6 * 109 years old Oceans are 4.2 * 109 years old Oldest rocks date from 3.8 * 109 years ago First evidence of life dates from 3.6 * 109 years ago 1 million = 1,000,000 or 106 Ocean and atmosphere reach the state we know today 800 * 106 years ago
Fig. 2-11, p. 49 13 16 75 Atmosphere unknown 50 Water Carbon dioxide 0 Nitrogen 25 Oxygen 4.5 3 4 Time (billions of years ago) 2 1 Early atmosphere quite different from today's Radioactive Decay Series Life probably originated in the ocean
Fossil of a bacteriabacterialike organism (with an artist's artist' reconstruction) that photosynthesized and released oxygen into the atmosphere. Among the oldest fossils ever discovered, this microscopic filament from northwestern Australia is about 3.5 billion years old. Parent Isotope Uranium-238 Uranium-235 Thorium-232
14 Stable Daughter Product Lead-206 Lead-207 Lead-208 Strontium-87 Currently Accepted Half-Life Values 4.5 billion years 704 million years 14.0 billion years 48.8 billion years
17 Rubidium-87 Billions of years ago 13 Big bang Billions of years ago 11 4.6 Earth forms Millions of Ocean forms years ago First galaxies 4.2 form 3.8 Oldest dated rocks 800 First animals arise 3.6 First evidence of life Solar nebula begins to form Earth forms Past
Millions of years 510 First ago 66 fishes End of dinosaurs Oxygen 2 appear revolution begins Pangaea 50 First marine breaks mammals Ocean and 210 apart 0.8 atmosphere End of reach steady dinosaurs state (as today) Humans appear 3 66 Today Today Today Sun's output too low for liquid-water ocean How long can Earth exist? The future of Earth 5.5 4.6 Today 0 Today 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. Age and Time Past and Future Future
3.5 The sun swells, planets destroyed 5 Billions of years in the future 15 Fig. 2-15, p. 51 18 3 Summary
Most 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.
19 Thinking Analytically
1. A light-year is the distance light can travel in one year. Light travels at 300,000 kilometers per second. Commercial television broadcasting began in 1939. Television signals travel at the speed of light. How far away would a space probe have to be before it could no longer detect those signals? 2. Can you think of any way an astronomer could detect a large planet orbiting a star without actually seeing the planet? (Hint how would a star move as the planet orbits it?) 20 4 ...
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- Spring '11
- Solar System, Gas Giant, Planet