this is from a textbook,ET2020 wrote: ↑Sun Mar 01, 2020 6:57 am There was a question on an invitational test about residence time that I'm confused about. On the answer key, they subtracted the output of the element from the input in order to get "net input", then divided the total amount of the element by the net input to get residence time. I thought net input was supposed to be zero, since a nonzero net input implies a change in total amount, and that residence time is just total amount/total input. Am I missing something here, or did they just screw up?
"residence time, the average length of time an atom of an element spends in the ocean.
Residence time for a particular element may be calculated by this equation:
Residence Time = Amount of element in the ocean/Rate at which the element is added
to (or removed from) the ocean.
Additions of salts from the mantle or from the weathering of rock are balanced by subtractions of minerals being bound into sediments. Dissolved salts precipitate out of the water, and the
hard parts of living organisms containing silicon and calcium carbonate drift slowly down to the seabed. Some of these sediments are removed from the ocean and drawn into the mantle at subduction zones by the cycling of crustal plates. Input (from runoff and outgassing) equals outfall (binding into sediments) for each dissolved component."