Rock Cycle

Types of Rocks

There are three main rock types, with rocks changing between each type over millions of years. 

Igneous rocks are formed from the cooling of molten rock (magma & lava)

• Magma cools underground → forms intrusive igneous rocks (e.g., granite).
• Lava cools on the surface → forms extrusive igneous rocks (e.g., basalt).

Sedimentary rocks are created when sediments (particles from weathered rocks, organic material, or minerals) are compacted and cemented together. Examples: Limestone, Sandstone

Metamorphic rocks are formed when existing rocks are exposed to heat and pressure. Example: Marble

 

Rock Transformations

Rocks transform between the igneous, sedimentary, and metamorphic types through natural processes in the rock cycle, driven by Earth’s internal and external forces.

Weathering and Erosion → Break existing rocks into smaller pieces, which are transported and deposited as sediments.

Compaction and Cementation → Sediments form sedimentary rocks

Heat and Pressure → Alters igneous and sedimentary rocks into metamorphic rocks.

Melting → If subjected to extreme heat, rocks melt into magma, then cooling forms igneous rocks.

 

Secrets Rocks Reveal

By studying rocks, geologists uncover a continuous story of Earth’s physical and biological changes.

Earth’s Age & Evolution: Rocks reveal Earth’s age (4.5 billion years) through radiometric dating and trace the evolution of life with fossils and mass extinction events.

Climate & Environments: Sedimentary rocks and isotopic analysis reveal past climates, environments, and significant changes, such as ice ages and lush swamps.

Tectonic Activity & Disasters: Rocks record tectonic movements, volcanic activity, and natural disasters, such as asteroid impacts and ancient eruptions.

 

Fun Facts

Here are some interesting facts about rocks:

• Marble, a metamorphic rock, starts as limestone but is transformed under pressure.
• The Grand Canyon’s layers are a stunning example of sedimentary rocks showing Earth’s history.
• Igneous rocks like obsidian, known as volcanic glass, were used to make ancient tools.
• Sedimentary rocks often contain fossils, offering clues about ancient life and ecosystems.

 

Review

Let’s quickly recap what we learned about the rock cycle:

• What type of rock forms from cooling magma? Igneous
• Which process transforms sediments into sedimentary rocks? Compaction
• What type of rock changes under heat and pressure? Metamorphic
• Which processes break existing rocks into smaller pieces? Weathering & Erosion