The Earth

8.1 The Earth and its atmosphere

Structure of the Earth (outside in):

• Crust — thin, solid outer layer.
• Mantle — hot, semi-molten rock; flows slowly.
• Outer core — liquid iron and nickel.
• Inner core — solid iron and nickel.

Atmosphere composition (clean dry air):

~78% nitrogen · ~21% oxygen · ~1% argon & CO₂ & water vapour

The crust + uppermost mantle are split into tectonic plates. Convection currents in the mantle move them very slowly. Where plates meet, you get earthquakes, volcanoes and fold mountains.

8.2 Sedimentary rocks

• Formed from layers of sediment (sand, mud, dead organisms) compressed and cemented together over millions of years.
• Often contain fossils and visible layers (strata).
• Examples: limestone, sandstone, chalk.

8.3 Igneous and metamorphic rocks

• Igneous: formed from cooled magma or lava. Interlocking crystals.
  • Cools slowly underground → big crystals (granite).
  • Cools quickly above ground → small crystals (basalt).
• Metamorphic: existing rock changed by heat and/or pressure (no melting).
  • Limestone → marble; mudstone → slate.

8.4 The rock cycle

Rocks transform from one type to another over geological time:

weathering → erosion → transport → deposition → compaction → sedimentary
(buried + heat/pressure) → metamorphic
(melted + cooled) → igneous
(uplifted + weathered) back to start

8.5 The carbon cycle

Carbon moves between living things, the air, the oceans and rocks.

• Photosynthesis: plants take CO₂ from the air → stored as glucose → made into plant tissue.
• Respiration (plants, animals, decomposers): releases CO₂ back to the air.
• Combustion: burning wood or fossil fuels releases CO₂.
• Feeding: carbon passes along food chains.
• Decomposition: dead material is broken down by microbes, releasing CO₂.

8.6 Global heating

• Burning fossil fuels and deforestation increase atmospheric CO₂.
• CO₂ and methane are greenhouse gases — they trap infrared radiation, warming the Earth.
• This extra warming is the enhanced greenhouse effect.

8.7 Climate change

Long-term shifts in global weather patterns. Effects:

• Melting ice caps → rising sea levels → coastal flooding.
• More extreme weather (heatwaves, storms, droughts).
• Habitats lost; species struggle to adapt.

8.8 Recycling

The Earth's resources are finite. Recycling means using materials again instead of extracting more raw material.

• Saves energy (often a lot — e.g. recycling aluminium uses ~95% less energy than extracting from ore).
• Reduces landfill and pollution.
• Conserves resources for the future.