Here's why:
* The rock cycle is a closed system: The processes within the rock cycle, such as weathering, erosion, melting, and cooling, only change the form of the existing rock material.
* Conservation of Mass: The fundamental law of conservation of mass states that matter cannot be created or destroyed, only transformed.
* Transformations: While rocks change form (sedimentary to igneous, igneous to metamorphic, etc.), the atoms that make up those rocks remain the same. They are just rearranged into different mineral structures.
Example:
* Sedimentary Rock: Sand grains (formed from weathering of igneous rocks) are cemented together to form sandstone.
* Igneous Rock: Sandstone is buried and melted to form magma. This magma cools and solidifies into granite.
* Metamorphic Rock: Granite is exposed to heat and pressure, transforming it into gneiss.
Throughout this process, the atoms that made up the original sand grains are still present in the final gneiss. They have just been rearranged through various geological processes.
