Answer to Question 1
Answer: The principle of superposition states that when rocks form at Earth's surface in layers, the lowest layer formed first and each successively higher layer is younger than the one below. The principle of original horizontality states that sedimentary layers are horizontal, or nearly so, when they are deposited. Non-horizontal layering indicates disruption of the beds at some time after deposition. The principle of cross-cutting relationships states that geologic features, such as dikes and faults, that cut across otherwise continuous rocks formed after the rocks that they cut across. The principle of inclusions states that objects enclosed by rock formed prior to inclusion within the rock.
Answer to Question 2
Answer: Relative ages establish the sequence of a series of events without establishing exactly when each event occurred. To establish relative age, items or events are placed in order of what happened first, what happened next, and what happened last. Absolute ages indicate exactly when an event took place. An absolute age is a specific age in years, or a statement that an event happened a particular number of years in the past.
A speculum used to hold the vagina open in order to visualize the cervix.
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The cascade of events by which the stroke-induced release of glutamate kills neurons.
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The Geologic Time Scale