Is it the biggest looming crisis that you have never heard of?
Since 1945, the world's population has tripled to seven billion, and feeding that population has relied increasingly on artificial fertilisers.
Phosphates, among the most important fertilisers, come from an ore that is in limited supply. It is mined, processed and spread on to our fields, whence it is ultimately washed away into the ocean.
So what will happen if one day we run out of the stuff?