F4 KI 2 d and e …. earth’s magnetic field ……

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Presentation transcript:

F4 KI 2 d and e …. earth’s magnetic field ……

F4 KI 2 d - specifications Some rocks contain a record of the direction of the Earth’s magnetic field at the time of their formation, known as remanent magnetism. This is linked to ferromagnetism in some iron minerals and their Curie temperatures

F4 KI 2 e - specifications Palaeomagnetism can be used to determine changes of latitude as different continents moved through geological time, indicating continental drift. Ocean floor magnetic anomalies indicate sea floor spreading.

Earth’s magnetic field https://www.youtube.com/watch?v=8llkHQtaOlg Bar magnet Geographic North Pole is where the lines of longitude cross Magnetic North Pole not at the same spot Precession http://www.youtube.com/watch?v=M9Gdm_OXKz4

Earth’s magnetism Liquid OUTER CORE generates the magnetic field for the Earth Earth’s magnetism is preserved in rocks Iron minerals in the rocks line up and preserve the direction of the magnetic field

How do rocks preserve the magnetic field? When rocks are molten, the iron minerals are free to move around As the rock starts to cool, these iron crystals ALIGN to the magnetic field of the time This is LOCKED in when the rock solidifies

Curie Point The temperature at which the iron minerals ALIGN in the molten rock Different for different rocks!

Earth’s magnetic field Is constantly moving North Pole moves in a predictable manner (PRECESSION) https://www.youtube.com/watch?v=0qHjtp4cdCA https://www.youtube.com/watch?v=Dw4Xhw4q4ec

Earth Learning Idea Polar wandering …..

Poles also FLIP Due to currents in the liquid outer core – the N/S can be flipped This has happened a lot in geological time It is recorded in rocks as normally magnetised rocks and reversely magnetised rocks

http://www.latimes.com/news/science/sciencenow/la-sci-sn-sun-magnetic-field-flip-20130807,0,7988373.story

http://www.bbc.com/earth/story/20141110-earths-magnetic-field-flips-more

Polar wandering Rocks which have the magnetic field preserved can be used to deduce their LATITUDE of formation and also point to where the N Pole was

Polar wandering As the plates move, the direction to the N Pole changes Graphs can be drawn which convert direction and distance into an easy to see pattern These are called POLAR WANDERING CURVES

Ages of solidified magma get older away from the mid ocean ridge (symmetrical pattern)

Age of crust is calculated (radioactive decay of minerals) See wall map….

http://www.bbc.co.uk/news/science-environment-26324968

Magnetic Stripes ·  After the Second World War geologists had the technology to study the sea floor.  They used ships and planes with magnetometers to measure the magnetic field above the ocean floor.  During the history of the Earth the direction of magnetic north has frequently changed/reversed.  Thus sometimes rocks are magnetised to the North and sometimes to the South.

Magnetic Stripes · It was found that rocks could be mapped as magnetic stripes parallel to the M.O.R. with alternating North and South magnetised rocks. These stripes were the same on either side of the M.O.R. i.e. they were mirror images. The rocks also got older as you moved away from the ridge.

http://www.nasa.gov/topics/earth/features/2012-poleReversal.html

Magnetic stripes

Iceland ridge

Scientists probe links between magnetic polarity reversals and mantle processes http://www.bbc.co.uk/news/science-environment-19514333

Palaeomagnetism Old magnetism Recorded in the rocks Pointer to where the magnetic pole was But – continents MOVE – plate tectonics So the rocks move with them Hence a movement track appears that the pole has moved, but it is really the rocks

Polar wandering curves

Magnetic Anomalies An ANOMALY is something we don’t expect to happen It is unusual and different to the expected data

Magnetic anomalies Something unexpected with the magnetic data Stripes in the sea floor

Diverging plate boundaries Symmetrical pattern of magnetic anomalies across ridge Mirror image heat flow (hot at ridge, cooling away from ridge) Thickness of ocean sediments gets thicker away from ridge Jigsaw fit

Africa: South America Jigsaw fit

Fossil and rock patterns in the jigsaw

GL1 Jan 2006 Q3

GL1 Jan 2006 Q3

GL1 Jan 2006 Q3