Lecture 2.1 The rock cycle

Earth Materials and Processes

• Earth processes are reliant on the properties of minerals and rocks.

• Key events influenced by rocks and minerals:

  • Volcanic eruptions

  • Mountain building

  • Weathering and erosion

  • Earthquakes

• Understanding earth materials is crucial for comprehending geological phenomena.

Clues from Rocks

• Rocks provide insights regarding their formation environments:

  • Rocks made from shell fragments indicate a marine origin.

  • Other rocks hint at volcanic events or mountain building.

• Rocks tell the story of Earth’s history through their composition and formation environment.

The Rock Cycle

• The rock cycle explains the transformation of rock types and is driven by:

  • Earth's internal heat engine (mantle movement)

  • Hydrological cycle (surface water movements powered by the sun)

• Active rock cycle is facilitated by:

  • A hot core that drives mantle convection

  • Presence of a relatively thick atmosphere and liquid water on Earth

• The rock cycles through several forms, allowing its components to change constantly.

Starting with Magma

• Magma is molten rock formed under high temperatures (800-1300 °C).

• Magma cooling leads to:

  • Intrusive igneous rock when cooled slowly underground.

  • Extrusive igneous rock when erupted and cooled quickly.

• Intrusive igneous rock must be uplifted and exposed for further transformation.

Weathering to Sedimentary Rock

• Exposure to weathering (physical and chemical) leads to:

  • Erosion and transport of small rock fragments.

  • Accumulation and deposition of sediments in various environments (rivers, lakes, oceans).

• Sediments undergo lithification, turning into sedimentary rock through:

  • Deposition: Accumulation of sediment when forces driving transport are overcome.

  • Compaction: Pressure from above materials forces grains tighter, expelling water.

  • Cementation: Minerals from groundwater act as glue, bonding sediment grains.

Formation of Metamorphic Rocks

• Metamorphic rocks formed under:

  • High temperature and pressure conditions that alter the material composition.

• The rock cycle illustrates that:

  • Both igneous and sedimentary rocks can be transformed into metamorphic rocks.

  • Metamorphic rocks can revert to magmatism, begin the cycle anew.

• Changes in rocks take extensive time, often millions of years, to occur.

Comparisons of Rock Types

• Igneous Rock

  • Forms either extrusively on the surface or intrusively beneath the surface.

• Sedimentary Rock

  • Created from accumulated and lithified sediments.

• Metamorphic Rock

  • Results from applying heat and pressure to existing rocks, capable of melting back to magma.

The Complexity of the Rock Cycle

• Pathways of transformation within the rock cycle:

  • Any rock type can transition into another through various processes.

  • Illustrates the interconnected nature of different rock types.

• The cycle presents multiple pathways; understanding these processes is essential for grasping geological changes.