Hoe and laser: what they have in common

1. Step 1. Hoe — evolved into — Plough. The plough mechanized loosening the soil with a hoe.
2. Step 2. Plough — is used in — Crop rotation. The three-field system with a heavy plough.
3. Step 3. Crop rotation — evolved into — Mineral fertilizer. Fertilizers solved the problem of fertility that crop rotation used to solve.
4. Step 4. Mineral fertilizer — is made of — Ammonia. Nitrogen fertilizers.
5. Step 5. Ammonia — is material for — Maser. The first maser ran on ammonia.
6. Step 6. Maser — evolved into — Laser. A laser is an optical maser.

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