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- mapping the ocean floor
- new ways to map invented in 1940s & 50s. sound waves allowed scientists to map large areas. Waves echo off the bottom- longer it takes sound waves to bonce back the deeper it is. translate into pict. Side-scan sonar waves use sound waves to produce a pict. of the ocean floor- picts show many features
- mid-ocean ridge
- a system of underwater mounatains with a deep creack running through them.-rift valleys
- mid-atlantic Floor
- runs along the floor of the Atlantic Ocean
- Rift Valleys
- places where lava erupts from the valleys along the mid-ocean ridges-creating a new ocan floor
- the scientist who developed the theory of the seafloor spreading moving and when?
- Harry Hess proposed in 1960s that less dense magma rose grom below the crust and forced its way up at mid-ocean ridges and rift valleys ..this molten material flows sideways carrying and pushing ocean floor ocean floor away from mid-ocean ridge cooling and creating a new ocean floor
- Rock ages
- in 1968 scientists aboard the Glomar Challange found the youngest rocks on the ocean floor were near mid-ocean ridges-farther from the ridges older the rocks
- What other evidence was found besides magnetic and rock ages
- life forms, giant tbe worms living on the ridges feeding off the chemical chemicals released from the valleys and ridges.
- Magnetic feild
- the earth's magnetic feild has a north and south pole. The feild is created as magnetic forces leave near the south Pole and enter the north Pole
- What happens if the poles reverse and how many times have they in the last _ years
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if poles reverse they leave north pole and enter south pole
reversed 9 times in last 3.5 million years - How is evidence found of the poles reversing?
- Igneous rocks forming along rift valleys and mid-ocean ridges register the earth's magnetic properties as the cool--Any changes or reversals will be registered in iron-bearing minerals
- magnetometer
- detects a strong magnetic reading when the polarity of a rock has the same polarity that the earth's magnetic feild presently has, normal polarties show up as peaks
- What did scientists find while using a magnetometer
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scientist found that rocks on the ocean floor showed many periods of reversals
reversals created matching stripes on either side of the mid-ocean ridge. - Magnetic Stripping
- shows the ocean floor is spreading formed at different times.. it is evidence to prove sea floor spreading.. showing the contenents can move
- Spreading Zones
- occur at mid-ocean ridges and rift valleys It is wehre oceanic crust is created and older crust is pushed away
- where do new rocks form and old rocks go
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mid-ocean ridges- new rocks
trenches- old rock subducted - Subduction
- process through which old oceanic crust is forced back into the earth at trenches
- How old are the oldest rock found on the ocean floor
- 250 million years
- How old are the oldest rocks found on continents?
- 3.6-3.9 billion years