Science Olympiad Dynamic Planet Practice Test

What is the primary composition of continental crust?

1. Rich in aluminum and silicon minerals

2. Dominated by basaltic rocks

3. Primarily made of ultramafic material

4. Composed of sedimentary deposits only

The correct answer is: Rich in aluminum and silicon minerals

The primary composition of continental crust is indeed rich in aluminum and silicon minerals, primarily in the form of granitic rocks. This composition is characterized by a higher concentration of lighter elements compared to the oceanic crust, which is mainly basaltic and denser. The minerals that dominate the continental crust include feldspar, quartz, and various other aluminum and silicon-rich minerals, which contribute to the lighter color and less dense structure of the continental crust. In contrast, basaltic rocks are more characteristic of oceanic crust, which primarily consists of denser materials that form under different geological conditions. Ultramafic materials, which contain a high percentage of iron and magnesium, are primarily found in the Earth's mantle rather than in the continental crust. Additionally, while sedimentary deposits do constitute a significant portion of the crust's surface landscape, the entire composition of continental crust includes igneous and metamorphic rocks as well, making it incorrect to say it is composed of sedimentary deposits only. Thus, the richness in aluminum and silicon minerals accurately describes the dominant features of continental crust composition.