GCSE Chemistry – The Planet Earth

C1b 6.1 The Structure of the Earth

    • The Earth is made up of layers that formed millions of years ago, when heavy material sank to the centre of our planet, and lighter material floated up to the top
    • The crust and the uppermost part of the mantle make up the Earth’s lithosphere
    • The crust is the outermost layer, ranging from about 6km under oceans to 35km under continents
    • The mantle, found under the crust behaves like a solid but is able to flow very slowly
    • The core is made up of two parts: the outer core and the inner core. They are both made of nickel and iron and the outer core is a liquid whilst the inner core is a solid

C1b 6.2 The Changing World

    • The supercontinent Pangaea is believed to have existed until 250 million years ago
    • Around 100 million years ago, Pangaea split into two vast continents: Laurasia and Gondwanaland were formed
    • 50 million years ago, and the continents as we know them today had formed, and carried on drifting apart
    • These land masses move because the lithosphere is cracked into a number of large pieces called tectonic plates
    • It is due to convection currents which push these plates over the Earth’s surface that the plates move a few centimetres each year
    • Convection currents are there because radioactive decay causes vast amounts of energy to be produced. This heats up molten minerals in the mantle which expand. They become less dense and rise towards the surface and are replaced by cooler material
    • When tectonic plates meet, earthquakes and volcanoes can happen C1b 6.3 The Earth’s Atmosphere in the Past
    • The early atmosphere was compressed into large amounts of carbon dioxide, water vapour, methane and ammonia (NH3)
    • When the Earth’s surface cooled below 100oC, the steam condensed to form oceans
    • As the oceans absorbed the carbon dioxide, the carbon dioxide concentration in the atmosphere fell dramatically
    • 3000 million years ago, simple plant life developed and by photosynthesis happening, the carbon dioxide concentration further dropped and oxygen produced
    • In the absence of air, temperatures that were about combined with the pressure formed fossil fuels, further reducing the carbon dioxide concentration
    • Shell formations in the oceans reduced carbon dioxide levels even more
    • Ammonia was removed via nitrification of bacteria (as they evolved), turning ammonia into nitrates
    • Denitrifying of bacteria turned the nitrates into nitrogen
    • Oxygen and ammonia also reacted to form water vapour and nitrogen

CH4 + 2O2 → CO2 + 2H2O 4NH3 + 3O2 → 2N2 + 6H2O

C1b 6.4 The Earth’s Atmosphere Today

  • The atmosphere on our planet is roughly the same as it was 200 million years ago: – 78% nitrogen
21% oxygen
0.9% argon
0.04% carbon dioxide
trace amounts of other gases

C1b 6.5 The Carbon Cycle

    • The carbon cycle shows how carbon rotates between the rocks, the oceans, and the atmosphere
    • The oceans absorb excess carbon dioxide and produce it when it is needed – making them useful carbon dioxide ‘reservoirs’
    • Plants also take in carbon dioxide during the process of photosynthesis
    • Therefore, plants and the oceans play good carbon dioxide sinks
    • Carbon dioxide is released back into the atmosphere when animals and plants respire, as well as when dead animal bodies decompose