Chapter 2 Origins

1. Chapter 2 Origins • Formation of Universe, Solar System and Earth • Creation of Oceans

2. 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

3. The Big Bang Theory is the dominant scientific theory about the origin of the universe. According to the big bang, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions.

4. 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.

5. Origin of a Galaxy • Huge rotating aggregation of stars, dust, gas and other debris held together by gravity.

6. Origin of the Solar System • Rotating cloud of gas from which sun and planets formed • Initiated by “supernova” = exploding star

7. 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

8. Moderate Size Stars (Our Sun): C & O Large Stars (more, H & He): Fe Supernova: Heavier Elements Formed

9. Origin of the Solar System • Rotating cloud of gas from which sun and planets formed • Initiated by “supernova” = exploding star

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. 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 system. Hydrogen and helium remain gaseous, but other materials can condense into solid “seeds” for building planets. The seeds of 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. Terrestrial planets are built from metal and rock. Solid “seeds” collide and stick together. Larger ones attract others with their gravity, growing bigger still. 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). Not to scale

11. Early Earth • Accretion (Gaining material) • Differentiation (Separating based on density  density stratification) • Evidence of water- 3.9*109 yrs ago

12. 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, and the crust.

13. How did water and water vapor form on early Earth? • The Sun stripped away Earth’s first atmosphere • Gases, including water vapor, released by the process of outgassing, replaced the first 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.

14. Sources of Water • Mantle rocks • Evidence from meteorites • Release through volcanic activity • Outer space • Evidence from Dynamics Explorer

15. 100 Methane, ammonia 75 Atmosphere unknown Concentration of Atmospheric Gases (%) Nitrogen 50 Water 25 Oxygen Carbon dioxide 0 1 3 4.5 4 2 Time (billions of years ago) Fig. 2-11, p. 49 The evolution of our atmosphere initial rise of O2 2.7 b. y. ago – but conclusive evidence is from 2.3 b. y. ago Early atmosphere quite different from today’s

16. Life probably originated in the ocean Fossil of a bacteria-like organism (with an artist’s 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.

17. Billions of years ago Billions of years ago Big bang 13 Earth forms 4.6 Millions of years ago Ocean forms 4.2 11 First galaxies form First animals arise 3.8 800 Oldest dated rocks 3.6 First evidence of life Past Solar nebula begins to form Millions of years ago 66 First fishes appear 510 5.5 End of dinosaurs Oxygen revolution begins 2 Earth forms 4.6 50 First marine mammals Pangaea breaks apart 210 Ocean and atmosphere reach steady state (as today) 0.8 End of dinosaurs Humans appear 0 3 66 Today Today Today Today Today Sun's output too low for liquid-water ocean Age and Time – Past and Future Future 3.5 The sun swells, planets destroyed 5 Billions of years in the future Fig. 2-15, p. 51

18. 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

19. Radioactive Decay Series Parent Isotope Stable Daughter Product Currently Accepted Half-Life Values Uranium-238 Lead-206 4.5 billion years Uranium-235 Lead-207 704 million years Thorium-232 Lead-208 14.0 billion years Rubidium-87 Strontium-87 48.8 billion years

20. The future of Earth • How long can Earth exist? • 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.

21. 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.