Earth's Structure Volumes and Composition

This question asks us to identify the incorrect statement among the given options about the Earth's structure and composition. Let's examine each statement to understand the key features of our planet.

Understanding Earth's Layers

The Earth is broadly divided into three main layers based on chemical composition:

• Crust: The thin, outermost rocky shell.
• Mantle: The thick layer beneath the crust, mostly solid but behaving like a very viscous fluid on geological timescales.
• Core: The innermost part, divided into a liquid outer core and a solid inner core.

Analyzing Volume Percentages

Let's look at the volume occupied by the mantle and core:

• Earth's Core Volume: Option 1 states the core occupies about 16% of Earth's total volume. This is very close to the accepted value, which is approximately 15% to 16% of the Earth's volume.
• Earth's Mantle Volume: Option 2 states the mantle occupies about 83% of Earth's total volume. The mantle constitutes the largest portion of the Earth by volume, estimated to be around 83% to 84%.

Based on these commonly cited figures, statements 1 and 2 are generally considered correct representations of the Earth's internal structure volumes.

Mantle Composition

Option 4 discusses the composition of the mantle. The Earth's mantle is primarily composed of silicate rocks that are rich in magnesium and iron. Peridotite is a dense, coarse-grained igneous rock that is believed to be the main constituent of the upper mantle. Therefore, the statement that the mantle is largely composed of peridotite is considered correct.

Continental Crust Density

Option 3 focuses on the average density of the continental crust. Let's analyze this:

• The Earth's crust is divided into continental crust (thicker, less dense) and oceanic crust (thinner, denser).
• The average density of the continental crust is typically cited as being around $2.7$ g/cm³ to $2.8$ g/cm³. While specific regions or depths might reach densities closer to $3.0$ g/cm³, the overall average is generally considered lower than this value.
• In contrast, oceanic crust has an average density of about $3.0$ g/cm³ or slightly higher.

Given that the statement specifies the *average* density of the *continental* crust as $3.0$ g/cm³, and standard geological data places this average slightly lower, this statement is the one that is NOT correct when compared to the widely accepted figures.

Conclusion

Based on the analysis of geological data regarding Earth's structure:

• The core volume is approximately 16%.
• The mantle volume is approximately 83%-84%.
• The mantle is largely composed of peridotite.
• The average density of the continental crust is generally accepted to be around $2.7$ g/cm³, not $3.0$ g/cm³.

Therefore, the statement "Average density of continental crust is $3.0$ g/cm³" is the one that is NOT correct.