Overview
This lecture covers the rock cycle, explaining how igneous, sedimentary, and metamorphic rocks transform into one another through geological processes, and introduces the concepts of weathering and erosion.
Types of Rocks & Their Origins
- There are three main types of rocks: igneous, sedimentary, and metamorphic.
- Igneous rocks form from the cooling of magma or lava.
- Sedimentary rocks form from sediments that are compacted and cemented.
- Metamorphic rocks form when existing rocks are altered by heat and pressure.
The Rock Cycle
- The rock cycle describes how rocks change from one type to another over time.
- Igneous rocks at Earth’s surface can be broken down by weathering and erosion to form sediment.
- Sediment is transported, buried, and lithified into sedimentary rocks.
- When rocks are subjected to high heat and pressure, they become metamorphic rocks, often during mountain building.
- Sedimentary and metamorphic rocks can also be broken down into sediment through weathering and erosion.
- Rocks in subducting slabs can return to the mantle, melt, and eventually re-form as igneous rocks through volcanic activity.
- The cycle is continuous and some mineral grains, like detrital zircon, have survived over 4.4 billion years.
Example: The Jack Hills Conglomerate
- The Jack Hills Conglomerate in Australia contains detrital zircon grains over 4.4 billion years old, showing the rock cycle’s longevity.
The Processes in the Rock Cycle
- Magma cools to form igneous rock.
- Igneous, sedimentary, or metamorphic rock can melt to become magma again.
- Weathering and erosion break down rocks into sediment.
- Sediments compact and cement to become sedimentary rock.
- High temperature and pressure convert rocks into metamorphic rock.
- The cycle repeats indefinitely.
Key Terms & Definitions
- Rock Cycle — the set of processes by which rocks transform between igneous, sedimentary, and metamorphic forms.
- Weathering — the breakdown of rocks at Earth’s surface by physical or chemical means.
- Erosion — the removal and transport of weathered rock material.
- Lithification — the process by which sediments compact and cement together to form sedimentary rock.
- Detrital Zircon — a durable mineral grain found in sedimentary rocks, known for its geological age.
Action Items / Next Steps
- Prepare to learn about the details of weathering and erosion in upcoming sessions.