6dc5455c____The_Coppermind___17th_Shard__Entry
[Chapter] 52 [Entry] 
Near the end, the ash began to pile up in frightening amounts. I've spoken of the special microbes that the Lord Ruler devised to help the world deal with the ashfalls. They did not "feed" on ash, really. Rather, they broke it down as an aspect of their metabolic functions. Volcanic ash itself is, actually, good for soil, depending on what one wishes to grow. Too much of anything, however, is deadly. Water is necessary for survival, yet too much will drown. During the history of the Final Empire, the land balanced on the very knife-edge of disaster via the ash. The microbes broke it down about as rapidly as it fell, but when there was so much of it that it oversaturated the soil, it became more difficult for plants to survive. In the end, the entire system fell apart. Ash fell so steadily that it smothered and killed, and the world's plant life died off. The microbes had no chance of keeping up, for they needed time and nutrients to reproduce.
The Hero of Ages/Epigraphs - The Coppermind - 17th Shard
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