Separated and dating again
Episodes of global volcanic activity, rifting of continents, folding, and metamorphism are defined by absolute ages.
Since parent uranium atoms change into daughter atoms with time at a known rate, their relative abundance leads directly to the absolute age of the host mineral.
Where this occurs at the edge of a continent, as along the west coast of North and South America, large mountain chains develop with abundant volcanoes and their subvolcanic equivalents.
These units, called igneous rock, or magma in their molten form, constitute major crustal additions.
By contrast, crustal destruction occurs at the margins of two colliding continents, as, for example, where the subcontinent of India is moving north over Asia.
Great uplift, accompanied by rapid erosion, is taking place and large sediment fans are being deposited in the Indian Ocean to the south.
A coin, vessel, or other common artifact could link two archaeological sites, but the possibility of recycling would have to be considered.