Our Changing Planet

Our Changing Planet

1. Structure of the Earth

   • The Earth is almost spherical with a diameter of about 128000 km
   • At the surface is a thin, solid crust
   • Crust = a very thin layer that varies in thickness between about 5km and 70km
   • The mantle is under the crust and is about 3000km thick - Goes halfway to the centre of the earth
   • The mantle almost entirely solid but parts of it can flow very slowly
   • The core is about half the diameter of the earth
   • The core has a high proportion of magnetic metals, iron and nickel - It has a liquid outer part and a solid inner part
   • The atmosphere surrounds the earth
   • Most of the air within 10km of the surface and most of the atmosphere is within 100km of the surface
   • All of the raw materials and other resources that we depend on come from the crust, the oceans and the atmosphere
   • This means the resources available to us are limited

2. The Restless Earth

   • Scientists now believe the Earth's crust and upper part of the mantle is cracked into massive pieces called tectonic plates
     • Tectonic Plates
   • Tectonic plates move a few centimetres a year because of convection currents in the mantle beneath them
   • The convection currents are caused by energy released by the decay of radioactive elements heating up the mantle
   • Where the plates meet, huge forces build up
   • Eventually, rocks changing shape or moving suddenly causing earthquakes, volcanoes or mountains to form
   • Scientists still do not know enough about what is happening inside the Earth to predict exactly when and where earthquakes or volcanic eruptions will happen
   • Alfred Wegener put forward the idea of 'Continental Drift' in 1915
     • Alfred Wegener - Continental Drift
   • Other scientists at the time did not accept his ideas, mainly because he could not explain why the continents moved
   • They believed the earth was shrinking as it cooled - In the 1960's scientists found new evidence and the theory of plate tectonics was developed

3. The Earth's Atmosphere in the past

   • Scientists think that the Earth was formed about 4.5billion years ago
   • In the first billion years, the surface was covered in volcanoes that released Carbon Dioxide, water vapour and Nitrogen
   • As the earth cooled, most of the water vapour condensed to form the oceans
   • Some scientists believe there was also nitrogen, and possibly some methane and ammonia
   • In the next two billion years, bacteria, algae and plants evolved
   • Algae and plants used carbon dioxide for photosynthesis and this released oxygen into the atmosphere
   • As the number of plants increased, the amount of carbon dioxide in the atmosphere decrease and the amount of oxygen increased

4. Life on Earth

   • The plants that produced the oxygen in the atmosphere probably evolved from simple organisms like plankton and algae in the ancient oceans
   • But we do not know how the molecules of the simplest living things were formed
   • Many scientists have suggested theories of how life began, but no one knows for sure because there is not sufficient evidence
   • In 1952 two scientists, Miller and Urey, did an experiment based on what scientists at that time thought was the early atmosphere
     • Miller & Urey
   • They used a mixture of water, ammonia, methane and hydrogen and a high voltage spark to simulate lightening
   • After a week, they found that amino acids (the building blocks for proteins) had ben produced
   • One other theory suggests that these organic molecules formed a 'primordial soup' and that the amino acids in this mixture combined to make proteins from which life began

5. Gases in the Atmosphere

   • Plants took up much of the carbon dioxide in the Earth's early atmosphere
   • Animals ate the plants and much of the carbon dioxide ended up in plants and animal remains as sedimentary rocks and fossil fuels (the CO2 formed sedimentary rocks)
   • Limestone was formed from the shells and skeletons of marine organisms
   • Fossil fuels contain carbon and hydrogen from plants and animals
   • Carbon Dioxide dissolves in the oceans and some probably formed insoluble carbonate compounds that were deposited on the seabed and became sedimentary rock
   • By 200 million years ago, the proportions of gases in the atmosphere had stabilised and were much more the same as hey are today
   • The atmosphere is now almost four-fifths nitrogen and just over one-fifth oxygen
   • Other gases including carbon dioxide, water vapour and nobelium's gases make up about 1% of the atmosphere
   • Separating the gases in air
     • The gases in the air have different boiling points and so can be separated from liquid air by fractional distillation
     • Fractional distillation of liquid air is done industrially to produce pure oxygen and liquid nitrogen, which have important uses
     • The air is cooled below -200c and fed into a fractional distillation column
     • Nitrogen is separated from oxygen and argon, and further distillation is used to produce oxygen and argon

6. Carbon Dioxide in the atmosphere

   • For about 200 million years the amount of Carbon Dioxide in the atmosphere has remained the same
   • This is evades various natural processes that move carbon dioxide into and out of the atmosphere had achieved a balance
   • These processes involve carbon compounds in plants, animals and the oceans an rocks
   • The organic carbon cycle shows some of these processes
   • Carbon dioxide dissolves in water, particularly the oceans, and reactions of inorganic carbonate compounds are also important in maintaining a balance
   • In the recent pasts, the amount of carbon dioxide that human activity has released into the atmosphere has increased dramatically
   • This has been mainly caused by the large increase in the amount of fossil fuels that we burn