and now they made a big comeback, although a lot of the bison we see, are crossed with beefalos. they are there is a genetic mix there. a sense of how important bones were to the fertilizer trade. a quick scientific foray. soil science is also critical to the story. i won't bore you with too many details. coming into the 19th century, scientists believed in the humus theory of soil fertility, the idea that it was fertile because of the organic matter and manure s that breakdown into it. this is a model of soil fertility that i think anyone is spent time doing organic farming would be familiar with. it made a bit of a return. chemist,man, a german insteade this and opted for a reductive soil chemistry that began to argue that fertile soils relied upon a couple critical nutrients. potassium, phosphorus. there will be a three number ratio, the ratio of those three elements. he is one of the ones that encourages us to think of fertilizer as more like vitamins then food. theory saw soil as something that needed to be fed. but no, it needed in fusions of these chemical, mineral element