1. Earth’s Atmosphere Noadswood Science, 2011

2. Earth’s Atmosphere To know how the Earth’s atmosphere has changed over time Tuesday, May 05, 2015

3. Atmosphere Word-search Complete the Earth’s atmosphere word- search…

4. Oxygen Percentage How much oxygen is in the air? Has it always been this amount – how can we tell? The percentage of oxygen in the air can be measured by passing a known volume of air over hot copper, and measuring the decrease in volume as the oxygen reacts with it Copper + Oxygen  Copper oxide 2Cu + O 2  2CuO

5. Oxygen Percentage *There is some air in the tube with the copper turnings – the oxygen in this air will also react with the hot copper, causing a small error in the final volume recorded *It is also important to let the apparatus cool down at the end of the experiment, otherwise the final reading will be too high

6. Atmospheric Evolution The Earth was formed about 4.5 billion years ago – its early atmosphere was probably formed from the gases given out by volcanoes It is believed that there was intense volcanic activity for the first billion years of the Earth's existence – the early atmosphere was probably mostly carbon dioxide, with little or no oxygen There were smaller proportions of water vapour, ammonia and methane

7. Atmospheric Evolution As the Earth cooled down, most of the water vapour condensed and formed the oceans It is thought that the atmospheres of Mars and Venus today, which contain mostly carbon dioxide, are similar to the early atmosphere of the Earth VenusMars

8. Earth’s Atmosphere Evolution Earth’s atmosphere has changed drastically over the last 4 billions years… Carbon dioxideMethaneAmmoniaNitrogenOxygen Others 4 billion years agoPresent day2 billion years ago

9. Atmosphere Changes The proportion of oxygen went up because of photosynthesis by plants The proportion of carbon dioxide went down because: - ▫It was locked up in sedimentary rocks, such as limestone, and in fossil fuels ▫It was absorbed by plants for photosynthesis ▫It dissolved in the oceans The burning of fossil fuels is adding carbon dioxide to the atmosphere faster than it can be removed meaning the level of carbon dioxide in the atmosphere is increasing

10. Nitrogen As oxygen levels rose atmospheric ammonia (NH 3 ) reacted with oxygen (O 2 ) to form water (H 2 O) and nitrogen (N 2 ) 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

11. Ozone Oxygen normally exists as pairs of atoms (O 2 ) Oxygen can, however, turn into another form that has three atoms joined together – this is ozone (O 3 ) 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

12. Atmospheric Changes 4 billion years agoPresent day3 billion years ago2 billion years ago1 billion years ago Volcanic activity releases CO 2, methane, ammonia and water vapour into the atmosphere The water vapour condenses to form oceans Green plants evolve which take in CO 2 and give out oxygen Carbon from CO 2 becomes locked up in sedimentary rocks as carbonates and fossil fuels. Methane and ammonia react with the oxygen and nitrogen is released. Nitrogen is also produced as a result of denitrifying bacteria on nitrates from decaying plants Volcanic activity releases CO 2, methane, ammonia and water vapour into the atmosphere. Some of the oxygen is converted into ozone. The ozone layer blocks out harmful ultra-violet rays which allows for the development of new life

13. Earth’s Atmosphere Evolution The Earth's atmosphere has remained much the same for the past 200 million years The main gas is nitrogen and oxygen (the gas that allows animals and plants to respire and fuels to burn) is the next most abundant gas These two gases are both elements and account for about 99% of the gases in the atmosphere – the remaining gases, such as carbon dioxide, water vapour and noble gases such as argon, are found in much smaller proportions

14. Carbon Cycle

15. The levels of carbon dioxide in the atmosphere have not changed must over the last 200 million years – this is due to the natural carbon cycle in which carbon moves between the oceans, rocks and atmosphere…