The Earth's Crust Is Named After Bread
A crust is the hard outer layer of bread. Geology borrowed the word for the thin solid shell of the planet.
A crust is a hard outer layer, above all of bread. Geology borrowed the image directly, and the proportion is right: the Earth's crust is thinner relative to the planet than the crust of a loaf is to the bread — around 35 kilometres under continents, against a radius of 6,371, which is roughly the thickness of an apple's skin. *To earn a crust* means to make a living, using bread as the whole of subsistence.
- The hard outside of bread. *A crusty loaf.*
- A pastry shell. *A pie crust.*
- The planet's outer layer. *The Earth's crust.*
- Earn a crust — to make a living. *Earning a crust.*
- Crusty — with a good crust, or bad-tempered. *A crusty old man.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | crust | A thick crust. |
| Plural | crusts | Cut off the crusts. |
| Adjective | crusty | Crusty bread. |
| Verb | encrust | Encrusted with salt. |
| Latin | crusta | A rind or shell. |
- The children left the crusts.Bread.
- The Earth's crust is thin and brittle.Geology.
- He earns a crust as a driver.Idiom.
The Earth in layers
- Crust — 5 to 70 km, thin and solid
- Mantle — about 2,900 km, hot rock that flows very slowly
- Outer core — liquid iron and nickel, the source of the magnetic field
- Inner core — solid, despite temperatures near the sun's surface
- Total radius — 6,371 km, so the crust is under one per cent
Old French *crouste*, from Latin *crusta*, a rind, shell or hardened surface. The geological sense dates from the 1500s.
How thick is the Earth's crust?
About 5 to 10 km under the oceans and up to 70 km under mountain ranges, against a radius of 6,371 km.
What does earn a crust mean?
To make a living. It is informal British usage, treating a crust of bread as bare subsistence.