I also missed this nice piece on Slate, where Sam Kean is blogging the Periodic Table. This episode was about nitrogen and nitrates, and then about phosphorus, and how we are probably running out of it. I have heard various estimates of when easily accessible resources will be finished, from 100 years to 30. Kean goes for 30. And sensibly, he arrives at the only possible conclusion as to where we will find replenishment: in the toilet.
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