Answer to Question 1
Answer: Magma forms only where unique circumstances exist that permit melting to occur in the mantle or lower crust. Partial melting of the mantle happens where rising mantle remains hot but is exposed to decreasing pressure at divergent plate boundaries and hot spots. Partial melting of the mantle also occurs due to the addition of water from metamorphic reactions during plate subduction at convergent plate boundaries.
Answer to Question 2
Answer: Combining field observation of rocks and modern processes with laboratory experiments revealed that certain graded sandstone beds interlayered with deep-water marine shale are the result of turbidity currents. Turbidity currents are mixtures of sediment and water that are denser than clear water and rush along the seafloor or lake bottoms. Solving some geologic problems requires integrating modern field observation and laboratory experimentation with study of ancient rocks and modern processes.
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Normal Faults Common at divergent plate boundaries
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Plate Tectonics
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Next-generation Illumina sequencing