GEOL 102 1st Edition Lecture 4Outline of Last Lecture I. Absolute DatingII. The Age of the EarthIII. Landscape EvolutionOutline of Current Lecture I. Landscape Evolution TheoriesII. Water and the Hydrologic CycleCurrent LectureI. Landscape Evolution TheoriesGrove Karl GilbertInteractions between process and formHilltops tend to be convexRiver profiles tend to be concaveLandscapes tend to erode at a ‘steady’ rateWilliam Morris DavisGeographical cycle: highly influential paradigm Mountains are uplifted and then decline through timeThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Young -> Mature -> OldStage 1: high mean elevation, low reliefStage 2: high elevation and relief as valleys catch upStage 3: valleys widen laterally, hill slopes degradeStage 4: featureless plain has been formed (peneplain)II. Water and the Hydrologic Cycle70% of the Earth’s surface is covered with waterHydrosphere: 1.36 billion cubic kilometers Ocean bottom to the troposphere is fifteen kilometers of elevationWater is a major constituent of life: ~60% of plants and animals is waterWater’s origin on Earth’s surfaceThe amount of water has been relatively constant throughout historyDirect evidence: ~4 billion year old sedimentary rocksMeteoric source of water1. Carbonaceous chondrites are ~20% water2. Heat released water vapor during the planet’s formation3. Other gases are released: primitive atmosphere4. After accretion slows (4.5 billion years ago) Earth’s surface begins to cool5. Liquid water accumulates on the surface6. Meteor bombardment continued until 3.5 billion years agoProperties of Water Atomic structure: 2 hydrogen atoms and one oxygen atomBondsMolecular: strong, covalent bonds hold atoms togetherHydrogen: weak bonds that act between water moleculesPolarityResults from unusual angleGenerates hydrogen bondsGas to liquid transitionHydrogen bonds form (and break and re-form)As temperature of liquid water drops1. Clusters of water molecules increase2. Packing and order increases3. Time spent in bond increasesFrozen Water (Ice)Bonding angle increases and density decreasesGeometry change to hexagonal patternImplicationsFrozen water floatsSolid form is less dense than liquid (expands by 9%)Critical to ocean and lake circulationLiquid water has a high heat capacityCan absorb or lose lots of energy without a large change in temperature Large bodies of water can absorb lots of radiationLatent heat of melting and vaporizationHeat is released when water freezes or vapor condenses Water exists in three phases on Earth’s surfaceKeeps temperature on Earth fairly stableWater exists as a liquid over much of the EarthWater is a universal solvent Many compounds dissolve due to attraction Surface tensionAdhesive tendencyWater molecules adhere to each other along