Database results:
examBoard: Cambridge
examType: IGCSE
lessonTitle: The Rock Cycle
The rock cycle is one of Earth's most amazing processes. It shows how rocks aren't permanent but are constantly changing from one type to another. Just like water cycles through different states, rocks also transform through various processes over millions of years. Understanding the rock cycle helps us make sense of our planet's geological history and how landscapes form.
Key Definitions:
Form when molten magma or lava cools and solidifies. Examples include basalt, granite and obsidian. These are often the hardest rock types.
Form when particles of other rocks or organic materials are pressed and cemented together. Examples include sandstone, limestone and coal.
Form when existing rocks are changed by heat, pressure, or chemical processes. Examples include marble, slate and gneiss.
Igneous Rocks
Igneous rocks begin their journey deep within the Earth where temperatures are high enough to melt rock into magma. When this magma cools, it solidifies into igneous rock. This cooling can happen in two main ways:
When magma cools slowly beneath Earth's surface, large crystals have time to form, creating rocks with visible mineral grains like granite. These rocks only become visible at the surface after overlying rocks have been eroded away.
When magma erupts onto the surface as lava and cools quickly, small crystals form, creating fine-grained rocks like basalt. Some cool so rapidly they form volcanic glass (obsidian) with no visible crystals at all.
Sedimentary rocks tell stories about Earth's past environments. They form through a series of processes:
Sedimentary rocks cover about 75% of Earth's land surface but make up only about 5% of the Earth's crust by volume. The rest is mostly igneous rock!
Sedimentary Rocks
Made from fragments of other rocks. Examples include sandstone (from sand), shale (from mud) and conglomerate (from pebbles).
Form when minerals precipitate from solution. Examples include rock salt and some limestones.
Form from the remains of plants and animals. Examples include coal and some limestones containing fossils.
Metamorphic rocks start as other rock types that are then transformed by heat, pressure, or chemical processes usually deep within the Earth's crust. The original rock (called the parent rock) changes in mineral composition and texture without melting completely.
Occurs when rocks come into contact with hot magma or lava, causing them to "bake" and change. This typically affects a relatively small area around the heat source.
Occurs over large areas, usually due to the pressure and heat created when tectonic plates collide. This forms mountain ranges and can affect rocks across hundreds of square kilometres.
The famous White Cliffs of Dover in England are made of chalk, a type of sedimentary rock formed from the shells of tiny marine organisms that lived millions of years ago. When these organisms died, their shells sank to the seafloor and accumulated. Over time, these remains were compacted and cemented together to form chalk. The cliffs demonstrate how biological processes contribute to rock formation and how geological uplift can expose seafloor sediments above sea level.
The rock cycle shows how rocks can change from one type to another through various Earth processes. There's no fixed path rocks can transform in multiple ways:
The rock cycle is crucial for many reasons:
Humans interact with and sometimes disrupt the rock cycle in several ways:
We extract rocks and minerals for construction, manufacturing and energy production. This accelerates erosion and changes natural landscapes.
Building dams, roads and cities changes natural erosion patterns and sediment transport. Concrete production also involves heating limestone, artificially speeding up certain rock cycle processes.
The atoms in the rocks around you have likely been recycled through the rock cycle multiple times over Earth's 4.5-billion-year history. The carbon atoms in limestone might once have been part of ancient marine creatures, then metamorphosed into marble, melted into magma and eventually returned to the surface as part of an igneous rock!
The rock cycle has no beginning or end it's a continuous process that has been occurring since Earth formed. It demonstrates how our planet is dynamic rather than static, with materials constantly being recycled and transformed. By understanding the rock cycle, we gain insight into Earth's past and can better predict its geological future.
Remember these key points:
Log in to track your progress and mark lessons as complete!
Login NowDon't have an account? Sign up here.