Which type of crustal material is the least dense?
a. Oceanic crust
b. Continental crust
The correct answer and explanation is :
The correct answer is:
b. Continental crust
Explanation:
The Earth’s crust is divided into two main types: oceanic crust and continental crust, each with distinct properties in terms of composition, thickness, and density.
Density Differences
- Oceanic crust is primarily composed of basalt, a dense and dark-colored volcanic rock rich in iron (Fe) and magnesium (Mg). Its density ranges from 3.0 to 3.3 g/cm³.
- Continental crust is mainly made of granite, a lighter-colored rock that contains more silica (SiO₂) and aluminum (Al). Its density is lower, typically around 2.7 to 2.8 g/cm³.
Because granite has a lower density than basalt, the continental crust is less dense than the oceanic crust.
Why Does Density Matter?
- The lower density of the continental crust causes it to “float” higher on the Earth’s mantle compared to the denser oceanic crust.
- This is why continents rise above sea level while oceanic crust forms the ocean floors.
- When oceanic and continental crusts collide (subduction zones), the denser oceanic crust is forced beneath the lighter continental crust, eventually sinking into the mantle and melting.
Thickness and Composition
- Oceanic crust is thinner (5-10 km thick) but denser.
- Continental crust is thicker (30-70 km thick) but less dense.
In summary, continental crust is the least dense type of crustal material, which is why it forms the landmasses that rise above the oceans.