Chapters 10 & 11- Geologic Time

Principle of uniformitarianism
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baked contactsan igneous intrusion cooks the invaded country rock- baked rock must have been there firstinclusionsalways older than the enclosing materialunconformitytime gap in the rock record; a period when no deposition occurred (but may have erosion)angular unconformity-rocks below the unconformity were tilted and folded before the unconformity developed -layers below the unconformity at a different orientation than layers abovenonconformity-sedimentary rocks overlie much older intrusive igneous and/or metamorphic rocks -igneous/metamorphic underwent cooling, uplift, and erosion and then sediments depositeddisconformity-parallel strata bounding nondeposition -due to an interruption in sedimentation (sea levels fall, then rises) -often hard to recognizegeologic column-composite stratigraphic column constructed from information around world= the geologic column -column divided in segments to represent time intervals=geologic times scaleeons-the largest subdivision of time (hundreds to thousands of Ma)phanerozoic-most recent eon -"visible life" -542 to 0 Mapaleozoic era-subdivision of phanerozoic eon -continents separate, sea levels rose and fell, continents rejoined to form Pangaea -Early: invertebrates with shell and jawless fish -middle: land plants and insects appear -end: land reptiles and treesmesozoic era-subdivision of phanerozoic eon -pangaea broke apart and atlantic ocean formed -dinosaurs prominent -during its cretaceous period: continents flooded, modern fish developed, mass extinction event wiped ou dinosaurscenozoic era-subdivision of phanerozoic eon -mountain building -various mammals -early humans appeared and evolved through the Pleistocene Ice Ageproterozoic-eon -"before life" -2.5 to 0.542 Ga -began 2.5 Ga -photosynthesis added oxygen to atmosphere -by the end of this eon, there were soft bodied marine invertebrates, and continental crust accumulated to supercontinentarchean-eon -ancient -3.8 to 2.5 Ga -began 3.85 billion years ago, when first continental crust that still remains formed -crust assembled out of volcanic arcs and hot spot volcanoes -atmosphere contained very little oxygen -first lifeforms appeared- bacteria and archaeahadean-eon -4.57 to 4.1 Ga -gravity pulled molten iron down to center of the Earth -planet was so hot that its surface was a magma oceanerassubdivisions of an eon (65 to hundreds Ma)periodssubdivisions of an era (2 to 70 Ma)epochssubdivisions of a period (0.011 to 22 Ma)life first appeared on earth3.8 billion years agonumerical age-age of rock in years -based on radioactive decay of atoms in minerals (radioactive decay proceeds at a known, fixed rate)how is numerical age measuredmeasured with isotopic dating techniquesisotopeselements that have varying number of neutronsstableisotopes that never changeradioactiveisotopes that spontaneously decayradioactive decay-half life-time for half of the unstable nuclei to decay -after one half life, half of the original parent remains -after 3 half lives, one-eight of the original parent remainsisotopic datinggives the time a mineral cooled below its closure temperature (when crystals cool enough to lock into lattice)start of the aging-cooling of magma or lava to solid, cool igneous rock -metamorphic rock temperatures drop below closure temp -sedimentary rocks cannot be directly datedage of the earth4.57 billion years ago based on correlation with meteorites and moon rocksoldest rocks on earths surface4.03 billion years agohumans occupy0.000001% of Earth history