Exposure dating uses the concentration of exotic nuclides (e.g.Cl) produced by cosmic rays interacting with Earth materials as a proxy for the age at which a surface, such as an alluvial fan, was created.The ocean plates spread and grow in opposite directions, so rocks that are equidistance from the center have the same magnetic polarity and age.That is, until they get subducted and recycled under less-dense oceanic or continental crust.(You may have heard this fact before, and while true, there is a logical explanation as to why.) Seafloor mapping, in its earliest, most primitive form, consisted of lowering weighted lines and measuring how far the sunk.This was done mostly to determine near-shore hazards for navigation.Geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves.Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is provided by tools such as palaeomagnetism and stable isotope ratios.
Both disciplines work together hand in hand however, to the point where they share the same system of naming rock layers and the time spans utilized to classify layers within a stratum.
By combining multiple geochronological (and biostratigraphic) indicators the precision of the recovered age can be improved.
Geochronology is different in application from biostratigraphy, which is the science of assigning sedimentary rocks to a known geological period via describing, cataloguing and comparing fossil floral and faunal assemblages.
It is the lasting remnant of an ancient ocean, the Tethys, that is shrinking as Africa and Europe collide in the Alpide orogeny.
At 280 million years, it still pales in comparison to the four billion-year-old rock that can be found on the continental crust.