Chapter 4 – Origins of Cosmic Structures and Chemical Elements

1. Chapter 4 – Origins of Cosmic Structures and Chemical Elements

2. Steady State or Evolutionary Cosmology • Steady State Universe Theory is no longer accepted. • Evolutionary Universe (Big Bang) Theory describes the origin of the universe.

3. Figure 4.CO: Messier 104 (Sombrero galaxy) Courtesy of NASA/JPL-Caltech and The Hubble Heritage Team (STScI/AURA)

4. Inflation • The universe is expanding. Fig 4.1 pg 66 Courtesy of NASA/WMAP Science Team

5. Table 4.01: The first 100 seconds in the life of the universe

6. The First 380,000 Years • The temperature of the “plasma” was initially too hot for electrons to combine with protons. • Once the temperature cooled enough, atoms could form. • Occurred in the “epoch of recombination,” about 380,000 years after the Big Bang. • Radiation was released, now know as the cosmic microwave background (CMB) • The universe is ~13.7 billion years old.

7. First Lights and the Formation of Galaxies • The first stars appeared ~200 My after the Big Bang • Gravity brings stars together into galaxies • Galaxies are named according to their shape. • Each galaxy merger leads to the formation of more stars.

8. Formation of Stars and Chemical Elements • 4 H+ join to form He, releasing energy. • Stars live on this reaction 90%+ of their lives. • A red giant is a star that has exhausted its supply of H+ fuel. • The core begins to condense. • When the core reaches a critical mass, it collapses. • It can become a neutron star, or a black hole. • Supernova is the explosion.

9. Galactic Chemical Evolution • The most common atom is hydrogen, left over from the Big Bang. • Many biologically important atoms are created by burning of elements in stars. Fig 4.4 pg 71

10. Shape and Future of the Universe • The average density of the universe is close to critical density. • Evidence suggests the universe is flat. • It is likely to expand forever.

11. Figure 5.01: Stages during the condensation of the solar nebula into the solar planetary system

12. Origin of Earth's Atmosphere • First atmosphere • Hydrogen and Helium, blown away by powerful winds from Sun • Secondary Atmosphere • 4.2 – 3.8 Bya • Volcanic output • Water vapor, carbon dioxide, carbon monoxide, nitrogen, ammonia, methane, hydrochloric acid, and hydrogen sulfide • Methane may have been byproduct of single-celled microbes called methanogens.

13. Origin of Earth's Atmosphere • Liquid Water • Formed when Earth cooled • C02 absorbed into oceans • Reducing • Excess hydrogen compounds provided electrons to oxidizing agents

14. Oxygen • Currently makes up 21% volume of atmosphere • Began increasing 2.3 Bya • Due to aquatic and photosynthetic cyanobacteria • Initially reacted with ammonia and iron • Then surplus began accumulating in atmosphere

15. Table 5.01: Present composition of Earth's atmosphere

16. Origin of Earth's Structure • Earth has four major layers • Inner Core • Outer Core • Mantle • Crust Fig 5.2 pg 80

17. Earth's Core • As planetesimals coalesced to form the Earth • Collisions and radioactive decay increased temperature • Partially molten • Heavy material (iron, nickel) sank inwards • Core 2,090 km thick • Outer Core • Responsible for Earth's magnetic field • Magnetosphere • Shields planet from incoming radiation

18. Earth's Lithosphere - Mantle & Crust • Mantle • 2,900 km thick layer of rock • 80% of Earth's volume • Partly plastic, ductile • From heat of radioactive decay and compression • Crust • Floats on mantle • Separated by Moho (Mohorovicic) discontinuity • Continental Crust, Older • Oceanic Crust, Younger Fig 5.3 pg 80

19. Earth's Crust • Three types of Rocks • Igneous : formed from molten rock (magma) • Granite – magma cools deep in crust • Lava – magma deposited on surface • 65% of Earth's Crust • Sedimentary : Particles of eroded igneous and other rocks, volcanic dust. • Sandstone, Limestone • 8% of Earth's Crust • Metamorphic : Rocks that have been transformed by excessive heat, pressure or chemical interactions. • Marble, Slate • 27% of Earth's Crust

20. Table 5.02: Some basic facts and figures concerning Earth

21. Origin of the Moon • Big Splash Theory • Planetesimal the size of Mars crashed into Earth on oblique angle • Part of the planetesimal and debris from Earth rebounded in space, coalesced • Gravity held moon to Earth

22. Geological Dating • Relative Dating • Law of Superposition • Youngest layers of strata on top • Oldest layers of strata on bottom • Layers can be identified by fossils • Lengths of time can only be estimated • Phanerozoic Eon (Phanero, visible & zoon, life) Fig 5.5 pg 83

23. Table 5.03: Geological ages and associated organic events

24. Radiometric Dating • Isotopes • A form of an element • Variations in number of neutrons • Number of protons dependent on element • Decay over time, releasing energy • Radiometric Dating • Half-life of isotope, time required to transform ½ of material • Provides ability to determine specific age of some rocks Fig 5.6 pg 86

25. Table 5.04: Radioactive isotopes used in dating

26. Origin of the Continents: Continental Drift • Pangaea • Large super-continent that began to break apart 235 • Evidence: • Fit of Continents • Similarity of rocks and fossils • Palaeomagnetism Fig 5.9 pg 89 Fig 5.8 pg 88

27. Paleomagnetism • Ferrous material magnetizes in cooling magma records • Records location and direction of magnetic field • Record of Earth's poles used to reconstruct continents location and movement through geological time Fig 5.10 pg 90

28. Figure 5.11: Diagrammatic sections through an oceanic ridge

29. Plate Tectonics • Tectonic Plates • Eight major plates have been identified • Plates separate • Lava creates oceanic ridges is space between moving plates • Plates slide past each other along fault lines • Plates collide • Subduction of one, uplift of other results in mountain building • Pangaea broke up as tectonic plates began to move • Separation of landmasses influenced biological evolution Fig 5.12 p 92

30. Figure 5.14: The major geological plates and their boundaries (From Cosmos, Earth and Man: A Short History of the Universe by P. Cloud, 1978, Fig. 11, p. 82. Reprinted by permission.)

31. Figure 5.15a: Collision of two plates, both with oceanic lithospheres

32. Figure 5.15b: Collision of two plates, one oceanic and one continental

33. Figure 5.15c: Collision of two plates, both with continental lithosphere

34. Figure 5.16a: Prototheria (monotremes)

35. Figure 5.16b: Metatheria (marsupials)

36. Figure 5.16c: Eutheria (placentals)

37. Biological Consequences of Plate Tectonics • Separation of organisms that were previously associated, results in unique evolutionary pathways • Mammals • Hairy skin, mammary glands • Prototheria (montremes) • Duckbilled platapus • Metatheria (marsupials) • Kangaroos • Eutheria (placental mammals) • Dogs, cats, humans Fig 5.17 pg 96

38. Origin of the Planets • Condensation Theory, Nebular Hypothesis • Solar System formed from mass of dust and gas • Started to condense 5-5.6 Bya • Center began to heat, to form Sun 4.6 Bya • Accretion Disk • Surrounding early sun • Planetesimals formed from condensation • Protoplanets and Planets formed from collisions of planetesimals Fig 5.1 pg 77