[Richard_East]

https://web.mit.edu/12.000/www/m2016/finalwebsite/solutions/...

"Earth's phosphorus is being depleted at an alarming rate. At current consumption levels, we will run out of known phosphorus reserves in around 80 years, but consumption will not stay at current levels. Nearly 90% of phosphorus is used in the global food supply chain, most of it in crop fertilizers. If no action is taken to quell fertilizer use, demand is likely to increase exponentially."

[petre]

It's not like it leaves the atmosphere and gets blown into space like Helium. I'm sure it collects in bones, plants, gets washed into the sea and it's generally just spread around.