we use fossils or ferromagneticminerals grains , the ramenent magnetisation tell us about the earth magnetic field , we can know the earth magnetic has changed during past , commen in these researches that use basalt that formed when lava congeals , ordinarly ,basalt contain hematite and magnetite, after lava congeals the rock continuous to cool ,when its tempreture drops to curie tempreture , the mineral magnetised by earth main field , these ramnent magntisation ramain at the same direction of earth field at curie tempreture , each grain become tiny magntic vector point to main field direction of its form , but in condition , not moved or tilted by tectonic plates because this alter ramnent magnetisation , by find all distribution of rocks specimens at same time , you can constructe the ancient magnetic field.
question : how can we know the time of magnetisation pf hand specimens ? easy , basalt usually contain some radioactive minerals like uranium and thorium , you can know the age of rock from these .... half live .....etc. usually the congeals of rocks is time close to its age of form
you can use sedimentary rocks , but know in your attention that sedimentary affected by weathering ....so oriented by earth field , know some geologic experience about magntism , you should firstly mark its place with arrows show the orientation , thin go to laboratory and use spinner magnitometer.......these magntometer removes induced
magnetization
alteration is very important to know....if the magntization affected easiky by other magntic fields you know that geologic event affected (alter) the main field.........small test to know that......raise the tempreture to curie tempreture , you can test the specimen and study the effect of thermal condition on ancient magnetism........from all these researches , geophysicists know that 1- the directin of earth magnetic field was reserved numerous times along age of earth......2-the magnetic poles position relative to varies continents has changed....... runcorn , one of pioneers of paleomagnetism , have said these (his researches is about magntic poles .........know from paleomagnetism data.
now let you with figues
change of earth magnetic field with age of earth
paleomagntism was used to know about plate tectonics...sea floor spreading....reversal of poles.
sea floor spreading
question : how can we know the time of magnetisation pf hand specimens ? easy , basalt usually contain some radioactive minerals like uranium and thorium , you can know the age of rock from these .... half live .....etc. usually the congeals of rocks is time close to its age of form
you can use sedimentary rocks , but know in your attention that sedimentary affected by weathering ....so oriented by earth field , know some geologic experience about magntism , you should firstly mark its place with arrows show the orientation , thin go to laboratory and use spinner magnitometer.......these magntometer removes induced
magnetization
alteration is very important to know....if the magntization affected easiky by other magntic fields you know that geologic event affected (alter) the main field.........small test to know that......raise the tempreture to curie tempreture , you can test the specimen and study the effect of thermal condition on ancient magnetism........from all these researches , geophysicists know that 1- the directin of earth magnetic field was reserved numerous times along age of earth......2-the magnetic poles position relative to varies continents has changed....... runcorn , one of pioneers of paleomagnetism , have said these (his researches is about magntic poles .........know from paleomagnetism data.
now let you with figues
change of earth magnetic field with age of earth
paleomagntism was used to know about plate tectonics...sea floor spreading....reversal of poles.
sea floor spreading