Dating of the Seafloor Methods to date the seafloor: Fossils--these give the age of the sediment layer enclosing them. The lowest fossils, just above the pillow basalts, will give the age of the crust. This requires basalt dating methods to the basalts. Radiometric dating--this gives the age of igneous and metamorphic rocks, for the last time they were heated enough to reset the radiometric clocks.
This requires a sample of the sea floor basalt hard access, even if not deeply buried by sedimentswhich are frequently hydrothermally altered hard analysis.