How much of a resource can you use every year to maintain a sustainable production?
It would be resource size divided by the number of years for the resource to replenish itself.
Take an old growth forest in which the life cycle of a tree is 400years. That means we can’t take more than 100*1/400 = .25% per year.
For an oil reserve we can’t use more than 100 * 1/ 10^9 = 10^-7 = .0000001 % per year assuming it takes a billion years to produce an oil reserve.
Some resources must be recycled as more is not being produced such as minerals deposits, the earth only came with a fixed amount of silver or gold for instance, and some of that is being thrown into space as space junk or non-returnable planetary landers. There is only a tiny fraction of metoric material falling on the earth in any given year.
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