Limestone can form whenprecipitates from water, or when sea shells or skeletons made ofaccumulate on the ocean floor. can form from skeletons of marine microorganisms that are made of silica, or when silica precipitates from water. Gypsum anddeposits can form in hot, dry climates when water trapped in closed basins evaporates.

1. crust 1 the metallic layer at the earth's center 2. inner core 3 the firm layer between the crust and the asthenosphere 3. lower mantle 2 the layer surrounding the inner core 4. asthenosphere 4 the semi-solid layer between the top layer and the upper mantle 5. upper mantle 5 the layer between the asthenosphere and lower mantle 6. top layer 6 the earth's outermost layer 7. outer core 7 the hottest part of the mantle