Earth’s atmosphere - step by step evolution

1 Earthlearningidea - s atmosphere - step by step evolutionUsing a physical model to show the development of our current atmospherePreparation: Using whatever materials are available, prepare balls of approximately 2cm diameter. This can betime-consuming but, once made, or assembled, they can be re-used many times. Suggestions are given in theResources list on page 4. You will need the following:- 74 green balls - water vapour 12 black balls - carbon dioxide 9 yellow balls - sulfur oxides 5 blue balls - nitrogen 3 red balls - oxygen 1 brown ball - argon 1 white ball - hydrogenAsk the pupils: Why is Earth s atmosphere important?

2 You could develop the discussion by using the followingsuggestions:- show that water is in the atmosphere by taking a glass bottle or jar from a refrigerator or boiling a kettle andholding a tile in the steam, to show that condensation is occurring; show that carbon dioxide is in the atmosphere by blowing into limewater to precipitate calcium carbonateturning the water milky; show a plant to prompt considerations of the end of the discussion, students should realise that the atmosphere is critical to life on Earth as we know the pupils to model the primeval atmosphere on Earth.

3 Tellthem that the gases in this early atmosphere are likely to besimilar to those produced by present day a sheet of A3 white paper, or in a tray, whichever is mostappropriate, place the following:-- 74 green balls - 74% water vapour- 12 black balls - 12% carbon dioxide- 9 yellow balls - 9% sulfur oxides- 5 blue balls 5% - nitrogen - 1 white ball (representing 0 4% hydrogen)- 1 brown ball (representing 0 2% argon)nitrogenhydrogencarbondioxideargon watervapoursulfuroxides o Primeval atmosphereDiscuss the composition of the atmospheretoday, as shown in the pie chart opposite. of other gases consists of hydrogen, ozone,neon, helium, krypton and xenon.

4 Water vapour isnot shown in this diagram because its amount in theatmosphere is the pupils: How will the atmosphere in theroom change if the room is sealed with everyoneinside?Through respiration, oxygen will diminish and carbondioxide and water vapour will of the atmosphere today nitrogen (78%)oxygen (21%)argon (0 9%)carbon dioxide(0 03%)other gases(0 07%) Earthlearningidea - the pupils to think about the composition of the currentatmosphere and to suggest how the primeval atmosphereevolved into it. Give them a sheet of A3 white paper divided intotwo sections, atmosphere and ocean, as shown in the diagramEvolving atmosphere following questions will help the pupils to place the colouredballs on the paper:- What happened to the water vapour?

5 Clue - Earth became cool enough for most of the water vapour tocondense as rain by 4000 million years ago. The primeval ocean was pupils should move all but one of the water vapour greenballs into the ocean. What happened to the carbon dioxide and sulfur oxides?Carbon dioxide and sulfur oxides are both soluble in rainfall sosome dissolved in the three carbon dioxide and two sulfur oxide balls to the evolving atmosphere should now look like the diagramEvolving atmosphere atmosphere 2nitrogenhydrogencarbondioxideargonwater vapoursulfuroxides o Evolving atmosphere 1nitrogenhydrogencarbondioxideargonwater vapoursulfuroxides o Evolving atmosphere 3nitrogenhydrogencarbondioxideargonwater vapoursulfuroxides o 4 6 - 5 billion years ago What effect did early bacteria have?

6 They evolved soon after the oceans early bacteria absorbed carbon and sulfur compoundsfrom the ocean water as they grew. When they died, they sank tothe ocean floor and the carbon and sulfur became locked up inocean-floor sediments. Add Ocean sediments to your diagramand move the balls as shown in Evolving atmosphere the pupils to compare the Evolving atmosphere 3 with thecomposition of the current atmosphere . What are the clear differences in the ratio of gases? What do they think happened?AtmosphereOceanAtmosphereOceanA tmosphereOceanOcean sedimentsEarthlearningidea - atmosphere 4nitrogenoxygencarbondioxideargonwaterva poursulfuroxides There is no oxygen in the evolving algae evolved in the oceans.

7 The early oxygenproduced by photosynthesis reacted with iron dissolved in seawater and precipitated out to form sea floor sediments, (fromabout billion years ago).The pupils should now put one red oxygen ball into the seafloor sediments. Where did the hydrogen go?Hydrogen is the lightest element; it rose into the upperatmosphere and was lost to space. The pupils should nowremove the white hydrogen ball. How did oxygen get into the atmosphere ?By 2 billion years ago, the iron in the oceans had absorbed all theoxygen it could, so free oxygen appeared in the atmosphere forthe first two red oxygen balls to the atmosphere - Evolvingatmosphere 4 What happened to the remaining carbon dioxide and sulfuroxides in the atmosphere ?

8 More and more became dissolved in the ocean and were thenlocked up in the ocean floor sediments. Move the black andyellow balls from the atmosphere into Ocean sediments .The final A3 sheet of paper should look like the one atmosphere is mostly nitrogen with oxygen and a little argonand has a similar ratio of gases to the current atmosphere . Theocean water has some dissolved carbon and sulfur oxides. Theocean floor sediments and the rocks that formed from themcontain carbon, sulfur and oxygen compounds. What about water vapour in the atmosphere ?Consider the water two green water balls from the ocean and return them tothe atmosphere as water vapour.

9 One could then condense andreturn to the ocean as back up:Title: Earth s atmosphere - step by step : Using a physical model to show the development of ourcurrent atmosphereTopic: This activity could be used in any lesson involvingdiscussions about the atmosphere or climate change andgreenhouse range of pupils: 14 - 18 yearsTime needed to complete activity: 30 minutes, longer with learning outcomes: Pupils can: construct a model of the primeval atmosphere ; suggest how our primeval atmosphere could have changed tobecome our current atmosphere ; realise that the amount of atmosphere around the Earth todayis considerably less than when there was a sedimentsOuter Earth todaynitrogenoxygencarbondioxideargonwat ervapoursulfuroxides atmosphere developed overthe last 1 billion yearsAtmosphereOceanOcean sedimentsEarthlearningidea - : This activity demonstrates the slowevolution from the primeval to today s up the activity: Pupils could investigate the atmospheres of ourplanetary neighbours, Mars and principles: Our current atmosphere contains 78% nitrogen,21% oxygen, argon and 0 03% carbondioxide.

10 The remaining 0 7% consists of hydrogen,ozone, neon, helium, krypton and xenon. Theamount of water vapour in the atmosphere isvariable, with a maximum of about 4%. The primeval atmosphere is likely to have beencomposed of the same gases that are derived frommodern volcanoes. Early water vapour condensed to form the oceans Carbon dioxide and sulfur oxides dissolved inwater and with early bacterial activity, much of itbecame locked into ocean floor sediments. Photosynthesis evolved and after early oxygen hadbeen absorbed by iron into ocean floor sediments, free oxygen escaped to the skill development: A pattern of evolution from the primeval atmosphereto our current atmosphere is developed.