1. The Early Atmosphere

2. Where did our atmosphere come from? Earth was formed around 4600 million years ago. We don’t know exactly, but the atmosphere was probably made up of hydrogen and helium. The Earth was a ball of molten rock. This probably caused the atmosphere to boil away into space.

3. The Earth was so hot that it probably remained molten for millions of years. Gradually, as it cooled, a solid crust formed. Molten rock often burst through this thin crust. Volcanoes were now erupting all over the Earth’s surface. They poured out lava and a mixture of gases – just as they do now. These gases formed the Earth’s atmosphere. The gases included ammonia (NH 3 ), carbon dioxide (CO 2 ), methane (CH 4 ) and steam (H 2 O). The atmosphere – around 4000 million years ago: mainly carbon dioxide lots of water vapour small amounts of methane, nitrogen and ammonia. Questions: 1.Give two differences between the Earth’s early atmosphere and the atmosphere we have today. 2.Explain why animals would not be able to survive in the Earth’s early atmosphere. The atmosphere – around 4000 million years ago: mainly carbon dioxide lots of water vapour small amounts of methane, nitrogen and ammonia.

4. Questions: 1.Give two differences between the Earth’s early atmosphere and the atmosphere we have today. 2.Explain why animals would not be able to survive in the Earth’s early atmosphere.

5. The Earth continued to cool. As it did so, the water vapour condensed and fell as rain. Hollows in the Earth’s crust filled up with this rainwater – these became our oceans.

6. Around 3000 million years ago, probably in the new oceans, the first living organisms evolved. These continued to evolve into simple plants like algae. The algae used up carbon dioxide in a process called photosynthesis and produced the Earth’s first polluting gas – OXYGEN. Gradually, the Earth’s atmosphere changed until about 200 million years ago the atmosphere reached the mixture we have today.

7. 3. From where did the early atmosphere originate? 4. What were the main components of the original atmosphere?

8. 5. What other substances were found in the atmosphere? 6. Name the Earth’s first ‘polluting’ gas. 7. What produced this polluting gas? 8. Explain why this gas is classed as being ‘polluting’.

9. What changes have taken place? The level has decreased dramatically. How? The carbon dioxide dissolved in the new oceans. It then concentrated into the shells of sea creatures as the compound calcium carbonate. Eventually these shells have become compacted together over millions of years to form limestone – a sedimentary rock. carbon dioxide

10. 9. Name the gas in the atmosphere that has seen the biggest (and quickest) change over time. The level has slowly increased. How? As more and more plants evolved, the process of photosynthesis increased. The plants use up carbon dioxide and produce oxygen. oxygen 10. Explain how this change came about.

11. 11. Name the gas in the atmosphere that has slowly increased over time. 12. Explain how this change came about.

12. Some of this new oxygen turned into ozone (O 3 ). This gas is found in the ‘ozone layer’ between around 15000 and 40000 km above sea level. Ozone is important since it filters out harmful ultraviolet radiation from the sun. Ultraviolet radiation can cause some skin cancers and cause cataracts to form in the eyes. Ozone