Solved cryptogram
Oxygen is not simply a gas. By mass it is the main ingredient of the rock beneath your feet.
Earth Science Facts, sourced to Royal Society of Chemistry.
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What it means
Just under half the mass of the Earth's crust is oxygen, bound into silicates and other minerals rather than floating free. The free oxygen in the air is a small fraction of the planet's total and is a biological product: for the first couple of billion years there was essentially none of it, until photosynthesis began releasing it faster than rocks could absorb it.
The claim comes from Royal Society of Chemistry.
- SourceRoyal Society of Chemistry
- CollectionEarth Science Facts
- Difficultymedium
- Length72 letters, 21 unique
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