WarmUp January 21 Write What You Know Write

Warm-Up January 21 • Write What You Know! – Write everything you know about the prompt below for five minutes, try for at least 3 -4 complete sentences. • On the ocean floors, where do you find older oceanic crust, and where do you find newer oceanic crust?

Sea-Floor Spreading Notes (Chapter 1. 4)

Sea-Floor Spreading • Mid-Ocean Ridge: – A landform found at oceanic divergent boundaries – An underwater chain of mountains – A place deep on the ocean floor that flourishes with bizarre life

Sea-Floor Spreading • Sea-Floor Spreading: – The sea-floor spreads apart along a mid-ocean ridge as new crust is added – Ocean floors move like conveyor belts, pushing the continents along with them

Sea-Floor Spreading • Evidence from Molten Material – Scientists have visited the mid-ocean ridge and observed rocks that form when lava cools rapidly underwater • Evidence from Drilling Samples – Drill samples show that rocks furthest away from mid-ocean ridge are older (rocks along the coasts), and rocks along the mid-ocean ridge are younger

Sea-Floor Spreading • Evidence from Magnetic Stripes – Earth’s magnetic poles switch over millions of years – Ocean floor rocks contain iron, which orients to the “North” pole when cooling from lava, forming magnetic stripes along the ocean floor

Sea-Floor Spreading • Deep-Ocean Trenches – A landform that occurs at ocean-continent convergent boundaries – A deep underwater trench that forms when the oceanic crust is subducted back into the mantle underneath the continental crust • Subduction – When oceanic crust sinks, melts, and is recycled back into the mantle