Earth Sciences 1022A/B Lecture Notes - Lecture 8: Half-Life, Unconformity, Metamorphic Rock
19 Oct 2016
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Superposition: each bed is older than the one above, and younger than the one below (diagram in notes) Original horizontality: sediment is usually deposited horizontally. Cross-cutting relations: (diagram in notes: a fault is younger than the rock it cuts, a rock is younger than the rock it cuts. Inclusions: inclusions are older than the rock containing them (diagram in notes) Places where rocks are missing, or formed but later eroded away (diagrams in notes) Angular unconformity: between at and tilted, eroded beds. Nonconformity: between at beds or eroded igneous, metamorphic rock. Fossil succession: organisms evolved along distinct pathways through geologic time, left index fossils (occur on a global scale, restricted to a speci c time frame) (diagram in notes) Radioactive isotopes (parents) decay to daughters over time (diagram in notes) Time it takes to decay to half the amount of parent left is the half life of the isotope. Compare parent left with half life, gives time since rock formed.
