Based on density, Sial is lighter than Sima.
The Earth's crust has historically been described in terms of two primary layers based on their chemical composition and density: the Sial and the Sima.
Understanding Sial and Sima
- Sial is a term derived from its main components: Silicon and Aluminium. This layer is often associated with the continental crust.
- Sima is derived from its main components: Silicon and Magnesium. This layer is typically associated with the oceanic crust and the layer beneath the Sial.
Why is Sial Lighter than Sima?
As the reference states, Sial has a lighter density than the Sima. This density difference is primarily due to their differing chemical compositions.
- Sial contains a higher proportion of lighter elements like Silicon and Aluminium.
- Sima contains heavier elements such as Silicon and Magnesium, as well as increased amounts of iron.
The reference confirms this: "Sial is lighter than Sima due to increased amount of aluminium, and decreased amount of iron and magnesium in it."
Composition and Density Comparison
Here's a simplified look at the typical composition and relative density:
| Characteristic | Sial | Sima |
|---|---|---|
| Main Elements | Silicon (Si) and Aluminium (Al) | Silicon (Si) and Magnesium (Ma) |
| Density | Lighter | Denser |
| Key Feature | Higher Aluminium; Lower Iron/Magnesium | Higher Magnesium; Increased Iron/Magnesium |
| Location | Predominantly Continental Crust | Predominantly Oceanic Crust & Below |
The difference in density between Sial and Sima explains why continental landmasses (composed mostly of Sial) float higher on the denser Sima layer beneath them, which forms the base of the ocean floors and underlies the continents.
