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

2. 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

3. 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.

4. Earth’s magnetic field
Bar magnet
Geographic North Pole is where the lines of longitude cross
Magnetic North Pole not at the same spot
Precession

6. 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

8. 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

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

12. Earth’s magnetic field
Is constantly moving
North Pole moves in a predictable manner (PRECESSION)

14. Earth Learning Idea
Polar wandering …..

15. 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

19. 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

21. 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

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

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

26. 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.

27. 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.

29. Magnetic stripes

30. Iceland ridge

31. Scientists probe links between magnetic polarity reversals and mantle processes

32. 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

33. Polar wandering curves

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

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

37. 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

38. Africa: South America Jigsaw fit

39. Fossil and rock patterns in the jigsaw

40. GL1 Jan 2006 Q3

41. GL1 Jan 2006 Q3

42. GL1 Jan 2006 Q3