Lecture Monday March 8, 2010 Radiocarbon is first produced in the atmosphere by collisions of neutrons with nitrogen atoms (nitrogen has 7 protons and 7 neutrons) Use radiocarbon dating->? 14 (top) C 6 (bottom)= radioactive = unstable produce by knocking out the particles in the nucleus 12 C 6= stable has 99% Radiocarbon produce in atmosphere. How do you date organics using carbon 14 dating= 1) beta counting (look at decay per min) 2) AMS dating measuring the ratio of the carbon 14 to carbon 13 to carbon 12 (all have 6 at bottom) can date little pieces. Radiocarbon dating useful for assigning ages to sediment that may incorporate organics during erosion? Radiocarbon dating useful for assigning ages to volcanic ash Radiocarbon dating is useful for capturing illegal contraband Next presentation (deformation) Permanent deformation of rock will occur when the applied stress exceeds the strength of the rock. Folding and faulting within the above bedrock are examples of permanent deformation. (similar to foam mattress press thumb let go takes a couple mins or sec go back to normal) like earth. Ex) rocks return to their original form Nonpermanent (elastic) deformation occurs in rock when weak stresses are applied. In such cases stress and strain are proportional. During the last glacial cycle (25,000-15,000 years ago) slide. Strandlines on Hudson bay= form due to wave erosion (storm) Northern great lakes are isostatically rebounding 5mm per year. Eventually it will be drained out to the Mississippi river. Two types of permanent deformation 1) brittle fracture (faulting) and 2) ductile fracture Control factors of ductile vs. brittle fracture deformation Temp Confining pressure (apply too much stress will break) Strain rate Lithology Time
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