| The motions of the tectonic plates can be tracked back through time by examining the magnetic signatures of rock samples. The differences between the orientation of the Earth's magnetic field recorded in the rocks of a particular age and today's magnetic field are used to reconstruct the locations of the continents at that time. The simple maps which result show the outlines of today's continents and continental shelves, but do not allow for variations of sea level, so they are just an approximation of the Earth's past geography. |