Chapter 5, Lesson 2 What are mid-Ocean ridges? What is sea-floor spreading? What happens at Deep ocean trenches?

Question: What are mid-ocean ridges? The form long chains of mountains that rise up from the ocean floor. They have been mapped using sonar (sound waves) All of earths oceans have these ridges They are the longest mountain ranges on earth Formed from magma leaking out a seam in the crust

Question: What is sea-floor spreading? Mid ocean ridges are continually adding new crust to the ocean floor. This causes the sea floor to spread out. At the same time, older strips of rock move outward from either side of the ridge What is the proof? The ocean floor contains “pillow” shaped rocks only formed by molten material Magnetic minerals found there come from magma Drilling has been done which shows older rocks away from the ridge and newer rocks along the ridge

Question: What happens at deep ocean trenches? The oceanic crust bends down into deep canyons known as deep ocean trenches Subduction Cooler/older crust is very dense causing it to sink back into the earth to begin the rock cycle again. The process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle Because of this process the ocean floor is renewed about every 200 million years.