There are children in the UK (and probably the US too) who think that food comes from grocery stores.

Most of you are smarter than that. You know that plant-based food grows out of the ground, and that animal-based food eats the plant-based food. You know that plant-based food needs oxygen and carbon dioxide and dirt to grow. Easy. You learned this in elementary school. Right? Nope, sorry.

Food comes from shit. Soil without shit in it is barren, sterile--you might as well try growing food on Mars if your soil lacks the shit it needs to produce healthy, thriving plants. Your soil might grow something, but probably not something you want to eat. Matt Damon knows the truth. 

These days, we add shit to soil via fossil-fuel based additions. The fertilizer you use in your garden and the fertilizer the farmer is using on his 400 acres of mono-crop corn is basically the same stuff. Fertilizer contains a mix of Nitrogen (N), Phosphorous (P), and Potassium or Kalium (K). Most plants we care about need a healthy amount of NPK to grow.

Brace yourselves now: I had to go do a ton of reading to understand what I'm about to write--you can bear with me for the four paragraphs of over-simplified science I condensed all that reading down to.

Most Nitrogen used in modern industrial farming comes from ammonia. The industrial production of ammonia is an energy-intensive process, requiring natural gas, significant heating, and significant cooling.

Industrial Phosphorous comes from a mineral that is extracted via mining and then converted to a usable salt via a sulfuric or phosphoric acid bath. This, too, is an energy-intensive process, inasmuch as creating the acid requires steady hot temperatures, as well as the industrial system needed to mine and transport large quantities of the basic minerals needed for these processes to occur. 

Potassium comes from Potash, which is a mineral that must be mined, usually from deposits deep under the surface, and then refined to separate the salt from the potassium.

The U.S. imports upwards of ten million tons of Nitrogen and five million tons of potash each year. Our imports of Phosphate, fortunately, are pretty minimal--we export a bunch of it. For reference, a small elephant can weigh about two tons. We're talking five million elephants of Nitrogen here, people.

What all that science stuff means is that we--meaning 'Merica--are in a world of hurt when it comes to sustainably producing our own food supply. It's true, fertilizer isn't made from petroleum products. We're not going to run out of fertilizer because we've run out of oil. What we are going to run out of is the ability to extract, refine, mix, and transport said fertilizer...because we've run out of oil.* And the pesticides, herbicides, fungicides, and so on that we must liberally apply to mono-crop fields that depend on those "ides" in order to ensure a decent crop yield. We also import a lot of food, though thankfully most of those imports aren't considered "staples."

Before many of the industrial processes of making fertilizer were invented, several of the modern(ish) nation states went bat shit over bat shit. Guano is a straight up super injection of NPK, without all the mining and refining (though there is definitely some nasty work and some transportation involved). Guano is still used in parts of the world, though not to the same extent it was in the 1800's. When industrial fertilizer took over from bat guano, we got a population growth that looks like this graph. Bat guano isn't going to sustain those kinds of population levels.

That leaves us in an interesting position where a significant portion of the global population may starve to death sometime in the next century. Famine: Not just for Africans anymore.

*Yes, this is a very simplistic way of looking at the situation.