GEOL 102 1st Edition Lecture 3Outline of Last Lecture I. Continental DrifII. Compositional EarthIII. Observations of the SeafloorIV. Plate TectonicsOutline of Current Lecture I. Absolute DatingII. The Age of the EarthIII. Landscape EvolutionCurrent LectureI. Absolute DatingRadiometric Techniques (1950s): technology stemmed from WWII weapons programsNaturally occurring isotopes: elements with different atomic weight (protons and neutrons), its weight is different than a standard isotope and because of this, they are unstable, so they’ll decay and breakdown. They account for a tiny fraction of mass in rocks or organic material.Radioactive Decay:Parent isotopes decay into daughter isotopesThese 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.Decay begins when rock cools to lower than its blocking temperature and isotopes can no longer escape crystal latticeHalf-life: time needed for half of a group’s isotopes to decayThe key for determining age is to determine the ratio of parent isotopes to daughter isotopes, comparing this with the half-life, and from this you can tell the ageDendrochronology: tree ringsMagnetostratigraphy: normal and reversed polarity timelinesFission tracksCosmogenic radionuclides: isotopes from cosmic raysRhythmic dating: annual layers or sediments can be countedII. The Age of the EarthHutton: measured time through sedimentation calculation, proves Earth is at least 20 million years oldLord Kelvin: measured time through cooling calculations, proves Earth is at least 20 million yearsoldSalt accumulation in Earth proves Earth is at least 90 million years oldOldest rocks on Earth (in Australia) are zircon crystals in sedimentary rock, proves Earth is at least 4.3 billion years oldMoon rocks: 4.4-4.5 billion years old, formed originally as one with Earth, moon rocks are preserved since they are not consumed by plate tectonic activityIII. Landscape Evolution~30 km thick crust is roughly when the crust is considered continental crust, not oceanicContinental crust “floats” on denser mantle rocksIsostatic uplif: removing mass by surface erosion makes the crust more buoyant, the mantlepushed it up more Crustal thickness is required to maintain mountainous topography Hills are convex, valleys are concaveLandscape DescriptorsDrainage density: length of channels divided by drainage amountRelief: difference between elevation of ridges and elevation of valleysSlope: how steep an incline is, rise over