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Ecology and Earth Science - The Rock Cycle

Grade 7IB

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

🔑Concepts

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The Rock Cycle is a continuous process by which rocks change from one type to another over geological time through processes like weathering, erosion, melting, and metamorphism.

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Igneous Rocks: Formed from the cooling and solidification of molten rock. If it cools underground, it is intrusive (plutonic); if it cools on the surface, it is extrusive (volcanic). Common minerals include Silica (SiO2SiO_2).

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Sedimentary Rocks: Formed through the accumulation of sediments that undergo lithification (compaction and cementation). Examples include Limestone, often composed of Calcium Carbonate (CaCO3CaCO_3).

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Metamorphic Rocks: Formed when existing rocks are subjected to intense heat and pressure without melting. This causes physical and chemical changes, often resulting in foliation.

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Weathering and Erosion: Mechanical or chemical breakdown of rocks. Chemical weathering can involve the formation of carbonic acid: H2O+CO2ightarrowH2CO3H_2O + CO_2 ightarrow H_2CO_3.

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Density (ho ho): A physical property used to identify rocks, calculated as the ratio of mass to volume: ρ=mV\rho = \frac{m}{V}.

📐Formulae

ρ=mV\rho = \frac{m}{V}

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

CO2(g)+H2O(l)→H2CO3(aq)CO_2(g) + H_2O(l) \rightarrow H_2CO_3(aq)

CaCO3+H2CO3→Ca(HCO3)2CaCO_3 + H_2CO_3 \rightarrow Ca(HCO_3)_2

💡Examples

Problem 1:

A student finds a sample of Basalt (an igneous rock) with a mass of 150g150g and a volume of 50cm350cm^3. Calculate the density ρ\rho of the rock.

Solution:

ρ=150g50cm3=3.0g/cm3\rho = \frac{150g}{50cm^3} = 3.0g/cm^3

Explanation:

Density is calculated by dividing the mass of the rock by its volume. This value helps geologists identify the mineral composition of the sample.

Problem 2:

Describe the chemical weathering of Limestone when exposed to acid rain containing Carbonic Acid (H2CO3H_2CO_3).

Solution:

CaCO3(s)+H2CO3(aq)→Ca(HCO3)2(aq)CaCO_3(s) + H_2CO_3(aq) \rightarrow Ca(HCO_3)_2(aq)

Explanation:

The solid Calcium Carbonate (CaCO3CaCO_3) reacts with the acid to form Calcium Bicarbonate (Ca(HCO3)2Ca(HCO_3)_2), which is soluble in water, causing the rock to dissolve over time.

Problem 3:

If a tectonic plate exerts a force of 5.0×109N5.0 \times 10^9 N over an area of 2.0×106m22.0 \times 10^6 m^2 during the formation of metamorphic rock, calculate the pressure (PP).

Solution:

P=5.0×109N2.0×106m2=2500PaP = \frac{5.0 \times 10^9 N}{2.0 \times 10^6 m^2} = 2500 Pa (or 2.5×103Pa2.5 \times 10^3 Pa)

Explanation:

Pressure is the force applied per unit area. High pressure is a primary driver for the recrystallization of minerals in metamorphic rocks.