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

2. 2 Formation of the Universe  Big Bang, 13*10 9 years ago  Formation of elementary particles  Gravitational formation of dense regions  1*10 9 yrs later  first stars

3. 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. 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. 5 Origin of a Galaxy  Huge rotating aggregation of stars, dust, gas and other debris held together by gravity.

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

7. 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. 8 Moderate Size Stars (Our Sun): C & O Large Stars (more, H & He): Fe Supernova: Heavier Elements Formed

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

10. 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. Hydrogen and helium remain gaseous, but other materials can condense into solid “seeds” for building planets. Cold temperatures allow “seeds” to contain abundant ice in outer solar system. Terrestrial planets are built from metal and rock. Solid “seeds” collide and stick together. Larger ones attract others with their gravity, growing bigger still. 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 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. 11 Early Earth  Accretion (Gaining material)  Differentiation (Separating based on density  density stratification)  Evidence of water- 3.9*10 9 yrs ago

12. 12 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. The result of density stratification: an inner and an inner and outer core, outer core, a mantle, a mantle, and the crust. and the crust. 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. Earth, Ocean and Atmosphere accumulated in layers sorted by density

13. 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. 14 Sources of Water *Mantle rocks  Evidence from meteorites  Release through volcanic activity *Outer space  Evidence from Dynamics Explorer

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

16. 16 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. Life probably originated in the ocean

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

18. 18 Age and Time 1 billion = 1,000,000,000 or 10 9 Earth is 4.6 * 10 9 years old Oceans are 4.2 * 10 9 years old Oldest rocks date from 3.8 * 10 9 years ago First evidence of life dates from 3.6 * 10 9 years ago 1 million = 1,000,000 or 10 6 Ocean and atmosphere reach the state we know today 800 * 10 6 years ago

19. 19 Radioactive Decay Series 48.8 billion yearsStrontium-87Rubidium-87 14.0 billion yearsLead-208Thorium-232 704 million yearsLead-207Uranium-235 4.5 billion yearsLead-206Uranium-238 Currently Accepted Half-Life ValuesStable Daughter ProductParent Isotope

20. 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. 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.