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Earth and Space - The Earth’s Structure and Atmosphere

Grade 7Cambridge (IGCSE)

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Earth is composed of four distinct layers: the Crust (outermost solid layer), the Mantle (thickest layer, semi-solid/plastic rock), the Outer Core (liquid iron and nickel), and the Inner Core (solid iron and nickel due to intense pressure).

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The Earth's atmosphere is a mixture of gases. The primary components are Nitrogen (N2N_2) at approximately 78%78\%, Oxygen (O2O_2) at 21%21\%, Argon (ArAr) at 0.9%0.9\%, and Carbon Dioxide (CO2CO_2) at 0.04%0.04\%.

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The atmosphere is divided into layers based on temperature gradients: the Troposphere (where weather occurs), the Stratosphere (containing the Ozone layer, O3O_3), the Mesosphere, and the Thermosphere.

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Atmospheric pressure decreases as altitude increases because there are fewer air molecules per unit volume (VV) at higher elevations, resulting in lower density (ρ\rho).

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Tectonic plates are large slabs of the Lithosphere (crust and upper mantle) that move over the Asthenosphere due to convection currents generated by heat from the Earth's core.

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The Ozone layer in the Stratosphere protects the Earth by absorbing harmful Ultraviolet (UVUV) radiation from the Sun.

📐Formulae

P=FAP = \frac{F}{A}

ρ=mV\rho = \frac{m}{V}

Volume of Gas=Percentage100×Total Volume of Air\text{Volume of Gas} = \frac{\text{Percentage}}{100} \times \text{Total Volume of Air}

T(K)=T(∘C)+273.15T(K) = T(^{\circ}C) + 273.15

💡Examples

Problem 1:

A sample of air has a total volume of 500 cm3500\text{ cm}^3. Calculate the approximate volume of Nitrogen (N2N_2) in this sample.

Solution:

Volume of N2=78100×500 cm3=390 cm3\text{Volume of } N_2 = \frac{78}{100} \times 500\text{ cm}^3 = 390\text{ cm}^3

Explanation:

Since Nitrogen makes up 78%78\% of the Earth's atmosphere, we multiply the total volume by 0.780.78.

Problem 2:

Explain why the Inner Core remains solid despite temperatures exceeding 5000∘C5000^{\circ}C.

Solution:

The Inner Core is solid because the extreme pressure (PP) at the center of the Earth forces the iron and nickel atoms together, preventing them from melting into a liquid state.

Explanation:

The melting point of metals increases with increasing pressure. At the Earth's center, the pressure is high enough to keep the core solid.

Problem 3:

If the atmospheric pressure at sea level is 101,325 Pa101,325\text{ Pa} and the force exerted by the air on a surface is 202,650 N202,650\text{ N}, find the area of that surface.

Solution:

A=FP=202,650 N101,325 Pa=2 m2A = \frac{F}{P} = \frac{202,650\text{ N}}{101,325\text{ Pa}} = 2\text{ m}^2

Explanation:

Using the pressure formula P=FAP = \frac{F}{A}, we rearrange it to solve for Area (AA).

The Earth’s Structure and Atmosphere Grade 7 Notes & Examples