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A primary question that can be asked about life:

A primary question that can be asked about life:. How did life originate? To ask this question using science (as opposed to other “ways of knowing”): What natural processes could account for the origins of life?. "We are Stardust". CHEMICAL EVOLUTION. Light energy. Heat. HO C H 2. OH.

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A primary question that can be asked about life:

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  1. A primary question that can be asked about life: How did life originate?To ask this question using science (as opposed to other “ways of knowing”):What natural processes could account for the origins of life?

  2. "We are Stardust"

  3. CHEMICAL EVOLUTION Light energy Heat HOCH2 OH H H O H H C C H C C O O H O O H O C H H H C C C H H O C C C O H H H O N H N H O HO OH H H C N Chemical Evolution • Early earth atmosphere and surface was composed of inorganic atoms and simple molecules. • Chemical evolution of these molecules produced the complex organic compounds that are the basis for life. 3. First carbon-carbon bonds 1. Simple molecules in atmosphere of ancient Earth 2. Reduced carbon- containing compounds

  4. The Structure of Atoms - Electron - - - Proton + + + Neutron - - - Hydrogen Carbon When the number of protons = the number of electrons: The positive and negative charges cancel each other out and the atom is electrically neutral

  5. The Structure of Atoms • Atomic and mass numbers indicate the identity of atoms Mass number = of protons + neurons He H 1 1 4 2 Be C N O F Ne Li 19 9 B 9 4 11 5 12 6 14 7 16 8 7 3 20 10 Atomic number = # of protons Na Mg Al Si P S Cl Ar 24 12 31 15 23 11 27 13 28 14 32 16 35 17 40 18 1 proton ≈ 1 dalton; 1 neutron ≈ 1 dalton

  6. The Structure of Atoms • All atoms of the same element have the same number of protons, but they may have different numbers of neutrons • Atoms of the same element with different numbers of neutrons are called isotopes • Example: • 12C • 14C

  7. Radioactive Isotopes allow us to determine the age of certain materials • Naturally-occurring radioactive materials break down into other materials at known rates. This is known as radioactive decay. • Once the rate of break down is known, geologists can estimate the length of time over which decay has been occurring by measuring the amount of radioactive parent element and the amount of stable daughter elements

  8. This graph shows how a sample of radioactive atoms decays with time. At the time a sample forms, the ratio of parent to daughter isotopes is 100:0. After the amount of time represented by one half-life passes, the ratio is 50:50; after two half-lives it is 25:75, after three half-lives it is 12.5:87.5, and so on.  Daughter isotope (gray) Parent isotope (red) 100 Percentage of parent isotopes remaining 50 25 13 6 0 1 2 3 4 Number of half-lives

  9. How electrons are distributed in an atom electron shells electron orbital 3 2 1 + the valence shell = electron = empty space

  10. Heat or light Ep (lower) ENERGY TRANSFORMATION IN AN ATOM Ep (higher) 1. An electron in an outer shell has a defined amount of potential energy, Ep- Ek 2. As the electron falls to a lower energy shell, its potential energy is converted to kinetic energy, Ek- 3. Once the electron arrives at a lower electron shell, the kinetic energy is converted to light or heat Energy is neither created nor destroyed; it simply changes form.

  11. Ions are atoms that have a charge Loss ofelectron Na+ Na+ Gain ofelectron Cl Cl Cl- Cl A sodium ion being formed Cation A chloride ion being formed Anion

  12. Ions of opposite charges are held together by ionic bonds Cl- Na+ Table salt is a crystal composed of two ions.

  13. Ionic solids dissolve readily in water d+ d- d- Na+ d+ Cl Cl- d+ d- d+ Water molecule

  14. Distribution of electrons in shells of these elements Hydrogen Helium Neon Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Phosphorus Sodium Chlorine Argon Magnesium Aluminum Sulfur Silicon The number of electrons in the valence shell of an atom determines its chemical reactivity.

  15. Sharing electrons between two atoms, in the form of a covalent bond, produces molecules. H H H H + Hydrogen atoms each have one unpaired electron H2 molecule has two shared electrons

  16. Water Oxygen Methane Ammonia Molecular formulas: NH3 CH4 O2 H2O H Structural formulas: N H O H C H H O O H H H H Ball-and-stick models: Space-filling models:

  17. How do chemical reactions occur? • Chemical reactions = the formation and breaking of chemical bonds: Reactant + Reactant  Products AB + CDAC + BD When the forward and back reactions occur at the same rate, the system is stable and is called a chemical equilibrium

  18. Chemical Reactions on Early Earth • It is thought that the early atmosphere was made of gases ejected from volcanoes • Volcanoes eject carbon dioxide, water, and nitrogen, along with some H2 and methane (CH4) • CO2 + H2O  H2CO3 (carbonic acid)

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