The reason both of these are valid scientific hypotheses is because A) scientists with different educational backgrounds may put forth different hypotheses to explain the same data.
This approach in science is vital in making progress and has helped to explain many phenomena in the past. When scientists explain data using different approaches, they come to a more comprehensive conclusion.
The breakdown of earths crust into sediment is called weathering.
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it is caused by relaxation of smooth muscle cells that are in the vessel walls which in the large arteries.