Magnetic reversals

Do your own fucking homework. Read your fucking textbook.

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>Asking for tech support or help with your homework.

>help with your homework.

>homework

>>77314
"Help", not "others will do it for you".
OP should post what he got so far so anons can correct or add new ideas.

Learn how to quote.

>>77314
>help
is not
>do it for me
We have no idea what notes you've been given on magnetism up to this point, nor how your text or teacher might link them to seafloor spreading.

>>77317
This is what I got so far.
The Seafloor Spreading Theory states that the alternating bands of rock resulted from the formation of new crust at the center of the mid-ocean ridge. The Mid-Atlantic Ridge occurs at a divergent boundary. Magma rises up through the gaps of the lithospheric plates and hardens. Over time the seafloor spreads out with new crust appearing along the boundary.
I don't know what it has to do with magnetism though.

File: Paleomagnetism.jpg (299KB, 1025x761px) Image search: [Google]

299KB, 1025x761px

>>77328
Geologist here. Yay! Cool stuff.

So. The poles of the Earth reverse every few hundred thousand years. We ... actually don't know why. It's weakening at the moment in the areas of South America so we think we're starting a new reversal.

Magma is rock that doesn't reach the surface of the Earth, it cools very slowly and so crystals can grow big. Lava is molten rock that reaches the surface and cools. Usually it weathers very quickly but sometimes lava is preserved in the rock record. Both magma and lava rocks are known as Igneous rocks.

Either way, lava or magma provides clues to Earth's paleo magnetism. We cannot do this process with the other types of rock, sedimentary or metamorphic rocks, just igneous.

When rock cools the crystals align to the magnetic poles. We can measure the magnetic orientation of any igneous rock on Earth and from that we can tell which direction was North when it cooled. Near the Mid Ocean ridges we tested the orientation of the poles when those rocks cooled and discovered they were in bands. These bands show both that the poles reverse and that the sea floor is spreading apart over time.

>>77340
Thanks. That helps a great deal. So for an answer in my own words, how's this?
By looking at samples of the crust in the ocean floor geologists found alternating stripes of igneous rock. Every other stripe had most of its magnetic molecules facing magnetic north. The remaining stripes contained magnetite molecules where the overall magnetism was in the opposite direction.

File: magnetite.jpg (580KB, 1024x768px) Image search: [Google]

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>>77345
Sounds good.

Although I would avoid the word 'magnetite' as it's an actual mineral type. We can use any igneous rock for paleomagnetism, not just magnetite. I'm guessing that was just a spelling error.