1. Fill in the blanks using words from the lesson. a. The rocks that make up the crust are relatively cold and ________________ b. S waves traveling through the crust and ________________ prove that these areas are not great reservoirs of molten rock. c. Seismic waves are refracted and _____________ at two distinct boundaries within the Earth. d. The mantle contains sixty-seven percent of the Earth's mass and eighty percent of its _________________________. e. A Danish scientist studying earthquake waves generated in _________________ discovered that P waves coming directly through the Earth speed up at a depth of 5140 kilometers. f. The mantle is composed of iron, _________________, aluminum, silicon and oxygen compounds. g. Sir Isaac Newton's explanation of __________________helped him determine that the rocks inside the Earth were denser than the rocks on the surface of the Earth. h. Scientists found that the travel time of earthquake waves differ greatly from predicted travel times if the Earth were of _______________ composition. i. The mantle lies between the ___________________ and the core and is divided into three regions. j. When the Earth was forming the ____________________ materials sank into the core and the lighter materials rose toward the surface. 2. Explain the composition of the earth. 3. Compare S (secondary) waves and P (primary) waves. Why do they travel at different speeds