Crop rotation and submarine: what they have in common

1. Step 1. Crop rotation — evolved into — Mineral fertilizer. Fertilizers solved the problem of fertility that crop rotation used to solve.
2. Step 2. Mineral fertilizer — uses — Sulfuric acid. Superphosphate is made with sulfuric acid.
3. Step 3. Sulfuric acid — is used in — Lead–acid battery. The electrolyte.
4. Step 4. Lead–acid battery — is part of — Submarine. Underwater, electric motors run on batteries.

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