Sea-Floor Spreading Chapter 9, Section 4 Chapter 9, Section 4 The Mid-Ocean RidgeThe Mid-Ocean Ridge Longest mountain chain in the world Longest mountain chain in the world It is almost entirely under water, but some areas do peak out of the ocean. It is almost entirely under water, but some areas do peak out of the ocean. Example – IcelandExample – Iceland

Sea-Floor Spreading As new rock emerges from the rift valley, older rock is pushed towards the edge of the ocean. As new rock emerges from the rift valley, older rock is pushed towards the edge of the ocean. o/animations/ch2.htm o/animations/ch2.htm o/animations/ch2.htm o/animations/ch2.htm

Molten Material – Pictures of molten material rising from the mid-ocean ridge have been taken. The molten material cools very quickly due to the contact with cold ocean water. hhhh tttt tttt pppp :::: //// //// wwww wwww wwww.... wwww wwww nnnn oooo rrrr tttt oooo nnnn.... cccc oooo mmmm //// cccc oooo llll llll eeee gggg eeee //// gggg eeee oooo //// eeee gggg eeee oooo //// aaaa nnnn iiii mmmm aaaa tttt iiii oooo nnnn ssss //// cccc hhhh hhhh tttt mmmm Evidence for S.F.S.

Magnetic Stripes in the ocean floor Earth’s magnetic poles (caused by the inner core spinning) have reversed themselves in the past. If they reverse again, our compasses will point south. hhhh tttt tttt pppp :::: //// //// wwww wwww wwww.... wwww wwww nnnn oooo rrrr tttt oooo nnnn.... cccc oooo mmmm //// cccc oooo llll llll eeee gggg eeee //// gggg eeee oooo //// eeee gggg eeee oooo //// aaaa nnnn iiii mmmm aaaa tttt iiii oooo nnnn ssss //// cccc hhhh hhhh tttt mmmm

Drilling Samples Scientist drilled the sea-floor to get rock samples. The older rocks were found far from the mid-ocean ridge. The younger rocks were found near the mid-ocean ridge.

Subduction at Deep-Ocean Trenches Subduction means to sink below. Subduction means to sink below. This allows the ocean floor to sink back into the mantle…a recycling of sorts. This allows the ocean floor to sink back into the mantle…a recycling of sorts. geo/egeo/animations/ch2.htm geo/egeo/animations/ch2.htm geo/egeo/animations/ch2.htm geo/egeo/animations/ch2.htm

Subduction and Earth’s Oceans The Pacific Ocean is SHRINKING !!! The Pacific Ocean is SHRINKING !!! More oceanic crust is subducted than is being produced, because there are more trenches.More oceanic crust is subducted than is being produced, because there are more trenches. The Atlantic Ocean is GROWING!!! The Atlantic Ocean is GROWING!!! More oceanic crust is being produced than subducted because there are fewer trenches.More oceanic crust is being produced than subducted because there are fewer trenches.