Sima Names the Rock Beneath the Ocean Floor
Sima is the dense lower crust of silicon and magnesium. Its name is a portmanteau.
Sima is a geological term for the dense lower layer of the earth's crust, which forms the ocean floors. The name is a portmanteau of its main elements, silicon and magnesium, coined alongside *sial* for the lighter continental crust of silicon and aluminium. Sima is denser, which is why continents float higher and why ocean crust subducts beneath them rather than the reverse. Both terms were coined by the Austrian geologist Eduard Suess in the early twentieth century.
- Dense lower crust. *The sima.*
- Sial — the lighter crust. *Sial.*
- Ocean floor rock. *Basaltic sima.*
- A portmanteau. *Silicon plus magnesium.*
- Eduard Suess — the coiner. *Suess.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | sima | The sima. |
| Related | sial | The sial. |
| Element | silicon | Silicon. |
| Element | magnesium | Magnesium. |
| Related | basalt | Basalt. |
- Ocean crust is sima.Geology.
- Sial is lighter.Contrast.
- The name combines two elements.Etymology.
Why continents sit higher
- Continental crust is granitic, lighter and thicker
- Ocean crust is basaltic, denser and thinner
- Both float on the denser mantle beneath
- The lighter crust rides higher, like a thicker raft
- At a collision, ocean crust dives under continental crust
A portmanteau of *silicon* and *magnesium*, coined by Eduard Suess alongside *sial*.
What is the difference between sima and sial?
Sima is the denser lower crust of silicon and magnesium forming ocean floors; sial is the lighter continental crust of silicon and aluminium.
Where does the name come from?
It combines the first syllables of silicon and magnesium, its two main constituents.