Science Olympiad Dynamic Planet Practice Test

What is the primary substance found in magma that forms Earth's crust and mantle?

1. Calcium

2. Silica

3. Iron

4. Sodium

The correct answer is: Silica

The primary substance found in magma that contributes significantly to the formation of Earth's crust and mantle is silica. Silica, or silicon dioxide (SiO2), is a major component of most igneous rocks, which are derived from cooled and solidified magma. In the context of geology, magma is composed of a variety of elements and compounds, but silica is the most abundant and crucial for determining the characteristics of the resulting rock. For instance, the viscosity, melting point, and overall behavior of magma during volcanic activity are heavily influenced by its silica content. High-silica magmas tend to be more viscous, leading to explosive volcanic eruptions, while low-silica magmas are more fluid and may result in less explosive lava flows. Silica also plays a critical role in the classification of rocks. Rocks with high silica content, such as granite, are typically found in continental crust, whereas lower-silica rocks, such as basalt, are prevalent in oceanic crust. This fundamental understanding of silica aids in recognizing the diverse geological processes that shape the Earth's crust and mantle.