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KS4 Changes to the Earth and atmosphere © Boardworks Ltd 2003 The Atmosphere © Boardworks Ltd 2003 In the beginning • The Earth was formed about 4500 million years ago. • The very first atmosphere mainly consisted of hydrogen and helium gases. • Frozen giant planets like Saturn and Jupiter still have atmospheres like this but on the warmer, smaller Earth these light gases were largely lost into space. Jupiter Saturn © Boardworks Ltd 2003 The early atmosphere • During the first billion years on Earth there was intense volcanic activity. This produced the next early atmosphere. • It would have contained large quantities of carbon dioxide (CO2), along with methane (CH4) , and ammonia (NH3). • This is rather like the atmosphere on Mars and Venus today. • The Earth’s atmosphere would also have contained water vapour which condensed to form the oceans. Mars Venus © Boardworks Ltd 2003 Oxygen levels increase • Carbon dioxide reacted with rocks and much became trapped in them. • The evolution of algae some 3000 million years ago, and subsequently plants which successfully colonised the Earth’s surface, led us towards the present atmosphere. • Their photosynthesis replaced carbon dioxide with oxygen. • Over a period of time billions of tonnes of carbon dioxide became locked up in fossil fuels. Earth Photosynthesis increased oxygen levels © Boardworks Ltd 2003 Nitrogen makes an appearance • As oxygen levels rose atmospheric ammonia (NH3) reacted with oxygen(O2) to form water(H2O) and nitrogen (N2) • Also, living organisms, including denitrifying bacteria, broke down nitrogen compounds releasing more nitrogen into the atmosphere. • And so the atmosphere headed towards a composition that has remained fairly constant for the last 200 million years. 21% 1% Nitrogen Oxygen Other 78% © Boardworks Ltd 2003 Ozone – a vital filter • Oxygen normally exists as pairs of atoms (O2). • Oxygen can, however, turn into another form that has three atoms joined together. This is ozone (O3). • As oxygen levels rose, so did the amount of ozone. • This layer of ozone in the atmosphere filters out harmful ultraviolet rays from the sun. This will have allowed new organisms to evolve and survive. 3O2 Oxygen 2O3 ozone Harmful UV rays stopped with ozone layer Earth Harmful UV rays reach Earth’s surface without ozone layer © Boardworks Ltd 2003 Activity Copy the timeline and arrange the blue boxes in appropriate places along the line. 4500 million No gases 3000 million H2O N2 O2 2000 million 1000 million CO2 NH3 CH4 500 million Volcanoes Algae 200 Now million H2 and He Plants © Boardworks Ltd 2003 Answer No gases Volcanoes 4500 million 3000 million H2 and He Plants Algae 2000 million CO2 NH3 CH4 1000 million 500 million 200 Now million O2 N2 H2O All positions are approximate © Boardworks Ltd 2003 Activity 1. What was the main gas in the atmosphere around 3500M years ago? Carbon dioxide 2. Where did this gas come from? Volcanoes 3. What process led to reduction in CO2 levels? Photosynthesis 4. What gas protects life from harmful UV radiation? Ozone 5. What % of the present atmosphere is oxygen? 21% © Boardworks Ltd 2003 Activity 1. How long ago was the atmosphere 75% CO2? Approx 4,000M 2. How long ago were the CO2 and N2 levels in the atmosphere equal? Approx 3,300M 3. How long ago was the atmosphere 50% nitrogen? Approx 2,000M 100% Composition percentage Use the graph to estimate the answers. carbon dioxide nitrogen 50% oxygen 0% 5000 3000 now 0 Time (millions of years) © Boardworks Ltd 2003 Activity Find the words in the word-search Write a sentence about how each has played a part in the evolution of the Earth’s atmosphere. P D E C O I T R N A F V Q M Z H E L I U M I O J W M B B K J O I Q E T M Q X Z V C B P F X T W R M E Y Z O A H K A N Y O O T Q T X L R Q L C G E G G Z S C H C B U Q G R T L E F K O Y A O M X Y O T U N N M I D N N S E U Y O E N J R T R O D E T W Z Q P E A M M O N I A K J H Y W M X T M G W O K I J Q S E B R E G E A X V W O B Z V W S T H N V I U M Y B N E L F J I H R D Z V P V K M W W R D R S E Q R X W K O N Z B P I P K Ammonia Carbon dioxide Helium Hydrogen Methane Nitrogen Oxygen Ozone Photosynthesis Volcano © Boardworks Ltd 2003 © Boardworks Ltd 2003 © Boardworks Ltd 2003 Carbon dioxide and temperature Over millions of years the carbon cycle has maintained a constant, low percentage (approx. 0.03%) of carbon dioxide in the atmosphere. In 1860, the CO2 level was about 289 ppm (parts per million). Here is a table showing the CO2 levels over a recent 10 year period. Year 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 Carbon Dioxide (ppm) 333.68 335.55 337.14 338.38 340.25 341.82 343.18 344.26 345.99 347.96 What percentage change is this and does it matter? © Boardworks Ltd 2003 Greenhouse effect From air trapped in Antarctic ice, we have a good idea of CO2 concentrations going back 160,000 years. We also know the temperatures over the same period. The very warm interglacial period of 130,000 years ago was accompanied by CO2 levels of around 300 ppm. The previous great Ice Age had CO2 levels around 200 ppm. 200ppm CO2 300ppm CO2 Which label goes with each picture? © Boardworks Ltd 2003 Greenhouse effect Normally the Earth absorbs heat and emits heat at the same rate. Because of this the temperature remains constant. Certain gases, like CO2 and methane, act like a greenhouse. They let heat in but do not let it out. This means: the more CO2 there is, the hotter planet Earth is! balanced same Earth temp More CO2 And hotter hotter! hotter Earth © Boardworks Ltd 2003 The Earth’s Structure © Boardworks Ltd 2003 The Earth’s Structure Beneath the atmosphere the Earth consists of 3 main layers: © Boardworks Ltd 2003 The core The core extends to about half the radius of the Earth. It is made mostly from iron and nickel and is where the Earth’s magnetic field comes from. It is very dense. 5500 C The temperature is high and the outer core is molten. Towards the centre high pressure makes the inner core solid. 1300 km Intense heat is generated in the inner core by decay of radioactive elements like uranium. 1110 km 3000 km Inner Outercore core © Boardworks Ltd 2003 The mantle The mantle extends outwards from the core to the crust: a distance of about 2,900 km. It is mostly a semi-molten liquid upon which the Earth’s crust floats. The heat coming from the core generates convection currents in the viscous mantle that cause the crust above to move. 2900km Mantle © Boardworks Ltd 2003 The crust The crust is the thin layer of rock at the surface upon which we live. Eight elements make up over 98% of the Earth’s Crust – although they are virtually entirely in the form of compounds. 50 % 45 40 35 30 25 20 15 10 5 0 20-60 km O Si Al Fe Ca Na K Mg Crust © Boardworks Ltd 2003 What am I? • I am dense, very hot, made mostly of solid iron and nickel. Inner core • I’m iron and nickel too, but I’m liquid. Outer core • I’m really very thin and am mostly silicon, Crust oxygen and aluminium • I’m a viscous semi-solid with convection Mantle currents circulating in me. • I just hang around on the outside. Atmosphere © Boardworks Ltd 2003 Attach labels to the correct part of the diagram. Atmosphere Outer core Crust Mantle Inner core © Boardworks Ltd 2003 Plate Tectonics © Boardworks Ltd 2003 Tectonic plates • • • • The crust is made of about twelve plates. These are like big rafts floating on the semi-molten mantle. Convection currents within the mantle cause the plates to move. Although they only move about 2 cm/year this can have huge effects over long periods of time. © Boardworks Ltd 2003 © Boardworks Ltd 2003 Sea floor spreading When two oceanic plates move apart molten rock rises to the surface. sea floor spreading oceanic plate magma rising © Boardworks Ltd 2003 Continental Drift • • • On average, the plates only drift about 2cm/year. However 2cm multiplied by a million is a long way! Scientists think the continents were originally all together in a supercontinent called Pangaea. Over millions of years they have drifted to their present positions on the floating tectonic plates. Pangaea Millions of years © Boardworks Ltd 2003 Continental Drift © Boardworks Ltd 2003 Evidence for Continental Drift The theory is supported by several pieces of evidence. For example, if we consider Africa and South America there is: – The “jig-saw fit” – The similarities in the rock layers from Africa and South America. – Similarities in the type and age of fossils. – Evidence of related species that definitely did not swim the Atlantic Ocean! Jig Saw fit Similar rocks and fossils © Boardworks Ltd 2003 Plate boundaries © Boardworks Ltd 2003 Effects at Plate Boundaries When a continental plate and an oceanic plate meet, the effects include: plates juddering past each other producing earthquakes the continental plate buckles upwards whilst the oceanic plate subducts (goes underground) volcanoes result from the rising magma (melted oceanic plate) volcano oceanic plate magma rising continental plate © Boardworks Ltd 2003 Activity • Find the words and write a sentence about how each one has something to do with plate tectonics. – Drift – Earthquake – Fossil – Jigsaw – Magma – Pangaea – Plates – Subduct – Volcano K L E I D M P Z P E G F M X R K L V A V F O S S I L A R N R N Q V U F Q T Q G A Z A O B T H E A A D P P L D Q S S M E G D C C U J I G S A W C X A C S A K P P L L K N T M W E F V I E E O A W F N X A S © Boardworks Ltd 2003