How Were the Earth and its Oceans Formed? The Origin of the Universe –Cosmic background radiation and expanding universe support the Big Bang Theory (origin of Universe ~ 13.5 bya) The Origin of the Earth and the Solar System –Solar system formed from nebula in Milky Way galaxy, with Earth forming from accretion of matter ~ 4.5 bya (based on age of oldest rocks from Earth and moon rocks) –Density stratification of Earth: solid inner core (iron and nickel), molten outer core, heterogenous mantle, and relatively thin crust –Moon was likely the result of an early cosmic collision The Origin of the Oceans and the Early Atmosphere –Cooling and outgassing of planet led to precipitation of water vapor and the formation of an early atmosphere Most carbon dioxide diffused into the ocean, leaving an early atmosphere of nitrogen gas Photosynthesis led to accumulation of oxygen by 1.5 bya –Ocean salts from erosion, runoff, and hydrothermal vents

Figures 3-3 to 3-5

Figures 3-6 and 6.1a

Why is Water so Important for Life? Water is a Polar Molecule (with + and – ends) –Hydrogen Bond: attraction between partial positive H atom (of one molecule) and unbound electrons or partial negative atom (of a separate molecule) Properties of Water (favorable for life) –Good solvent: water is polar (negative and positive ends)  breaks ionic bonds and makes ions available for organisms (ex. calcium from calcium carbonate, sodium from sodium chloride) –Cohesive: molecules of water “stick together” (results from hydrogen bonds)  good medium for chemistry and high surface tension Top mm of ocean/lakes with highest abundance of photosynthetic microbes, many organisms can float on surface –High thermal capacity: resists temperature changes; stable for life –Unique density: becomes less dense upon freezing (ice floats); allows life to exist under ice when air is far below freezing Water is the Matrix of Life –Known to be on Mars (frozen) and Europa (moon of Jupiter)

Figure 6-7

Figures 6-8, 6-9, and 6-12

The Origin of Life: How? When? Where? From the Pre-biotic Soup to Proto-cells (Oparin-Haldane) 1.Formation of large organic compounds from “interstellar-type” compounds (amino acids formed from methane, water, ammonia, and hydrogen gas with electric spark as energy source - Stanley Miller, 1953) 2. Formation of organic polymers (biochemicals) from large organic compounds (some polymerize in presence of metal catalysts, but small yields) 3. Internalization of metabolites within lipid membrane (phospho- lipids and fatty acids spontaneously form hollow spheres in water, and internalize certain compounds) The Importance of RNA –RNA a simpler compound than DNA, can do cellular work (like an enzyme), and can evolve in response to selection –Ribosomal RNA is conserved in all living things; RNA nucleotides involved in the energy systems of all cells (ex., ATP)

Figure 3-8

The Origin of Life: How? When? Where? The Heterotroph Hypothesis: first living cells were likely heterotrophic vs. autotrophic (complex metabolism) The Fossil Record for Early Life –Oldest confirmed fossils of cells ~ 2 billion years old (stromatolites); older fossils (~ 3.5 billion years old) relatively controversial –Indirect indications of life (bioindicators) suggest life present by 3.5 billion years ago Graphite particles rich in carbon-12 from rocks in Greenland Banded iron formations (redbeds) suggest that oxygen gas reached ~ 15% of present-day level by 2.5 billion years ago (regarding formation of rust in presence of iron, water, and oxygen gas) Where did Life Originate? –Pre-biotic soup (“warm little pond” or “cold pond”?); water is the “matrix of life” (properties conducive for life) –Hydrothermal vents and springs: both home to ancient forms of microbes (chemosynthetic thermophiles) –Panspermia Hypothesis: first cells arrived via meteorite?

Is There Life in Outer Space? The Search for Life in Outer Space (astrobiology) –Existence of extra-terrestrial microbes thought to be more likely than in past, due to diversity of extremophiles on Earth (“life finds a way”), and presence of organic compounds, water, and energy sources in outer space (vs. “Goldilocks argument”) Bacteria omnipresent: found in all extreme environments on Earth –Temperature: -2 to 121°C (ice caps, hydrothermals; experimental evidence) –Pressure: up to 1600 MPa (experimental); microbes cultured from deep-sea and from crustal fluids –Dryness: endolithic microbes in deserts of Peru and Antarctica (0% humidity) –Salinity: 15-37% NaCl (soda lakes) –pH: as low as 0.7 (sulfur springs) and as high as 12.5 (soda lakes) –Locations of Interest: Mars (polar ice caps, recent evidence of more widespread water in past); Europa (Jovian moon – “snowball” with liquid beneath ice, likely volcanic activity and magnetic field) The Search for Intelligent Life in Outer Space –Search for Extra-Terrestrial Intelligence (SETI) Drake Equation: formulated by Frank Drake in 1961 as an estimate of the number of communicating civilizations in the Milky Way galaxy; estimates range from 1 to 1,000,000 (C. Sagan); Drake’s ~ 10 Listen for abnormal signals of extra-terrestrial origins via radio telescopes; digital signals sent out in 1974 and 1999; Voyager spacecraft (2) contain messages on discs (now beyond solar system); project allows individuals to help analyze data (noise)