Respuesta :

  the  sea  floor record  the  magnetic  reversals  over time  by Iron  rich  mineral  in   lava   cools. then  crystallize  finally  land  record  earth  magnetic  polarity.  Evidence  suggest  that  the  magnetic  field  has  periodically reversed it  polarity  in  the past. When  reverse  patches grow  to  a  point  that  they  dominate  the rest  of  the  core  earth  overall  magnetic  field  flips.
When new seafloor is created by upwelling magma at the mid-ocean ridges, the magnetic minerals orient themselves to the magnetic orientation of Earth at the time of their solidification in the rock matrix. Thus, the history of magnetic reversals are recorded in the rock.