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.
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, and the page it comes from was read on 2026-08-27 to confirm it still says this.
This is not the kind of claim that goes out of date, which is why it was set as a puzzle rather than a fact with a shelf life.
Solve it yourself
This fact is a cryptogram here: 72 letters over 21 different ones, graded medium.
- SourceRoyal Society of Chemistry
- CollectionEarth Science Facts
- Difficultymedium
- Length72 letters, 21 of them different
Nearby in the collection
The facts either side of this one.
- Royal Society of Chemistrymedium, 75 letters
- NASAmedium, 76 letters
- NOAAhard, 73 letters
- NOAAmedium, 74 letters
About as hard as this one
Scored closest to it by the model behind our guide to solving cryptograms.
- NOAAmedium, 67 letters
- U.S. Geological Surveymedium, 79 letters
- NASAmedium, 74 letters
- U.S. Geological Surveymedium, 78 letters