Silica and Magnesium
Explanation
The Earth's crust is chemically classified based on the dominance of specific mineral elements. The terms 'Sial' and 'Sima' were historically introduced by geologist Edward Suess to distinguish between the composition of the continental and oceanic crusts.Detailed Analysis:
- Sima: The term is an acronym derived from the first two letters of Silica and Magnesium. It refers to the layer of the Earth's crust that is dominated by basaltic rocks rich in these elements. This composition is characteristic of the oceanic crust and the lower continental crust.
- Sial: In contrast, the upper layer of the continental crust is known as 'Sial' (Silica and Aluminium), which is granitic in nature.
- Density Difference: Sima (approx. 3.0 g/cm³) is denser than Sial (approx. 2.7 g/cm³). This density difference is a fundamental concept in understanding isostasy and plate tectonics.
Key Takeaway: 'Sima' stands for Silica and Magnesium, representing the denser, basaltic rock layer that primarily constitutes the oceanic crust.