Answer to Question 1A terrestrial sequence of magnetic reversal in volcanic deposits was dated radiometrically. These dates
were extrapolated to regions which were not dated, but showed the same pattern of normal and
reversed magnetic polarities. Ages of ocean-floor basalts lying within a zone of normal or reversed
polarity are dated by the ages of the fossils found in the sediments that directly overlie the basaltic
crust. These fossils have already been incorporated within a biostratigraphic zone.
Answer to Question 2With seafloor spreading, the continents and oceanic crust move together as part of large plates. The
plate is pushed by the formation of new ocean crust and pulled by the subduction of old ocean crust.
New crust forms due to seafloor spreading.