Rocks and Fossils

Structure of the Earth – Modern Model  

- Crust → solid, made of different types of rock.  

- Mantle → solid but flows very slowly, extends halfway to Earth’s centre.  

- Outer Core → liquid, made of iron and nickel.  

- Inner Core → solid, mainly iron and nickel.  

- Temperature increases from crust to core (deep mines in South Africa ~60°C at 4 km depth).  

The Earth’s Crust  

- Made up of different types of rock.  

- Uses:  

  - Some rocks are used directly (building, construction).  

  - Metals extracted from ores.  

  - Rocks processed into cement and materials.  

- Rocks classified into three groups:  

  1. Igneous  

  2. Sedimentary  

  3. Metamorphic  

Igneous Rocks – Properties  

- Formed when magma cools and solidifies.  

- Hard, durable, non‑porous (no gaps between interlocking crystals).  

Examples:  

- Granite → large visible crystals, strong.  

- Basalt → tiny crystals (cooled quickly), hard, durable, used as railway ballast.  

  - Fun fact: Giant’s Causeway in Northern Ireland formed from basalt.  

Sedimentary Rocks – Properties  

- Formed from grains held together loosely.  

- Porous → spaces between grains filled with air or water.  

- Softer than igneous rocks, easier to scratch.