C9

• oxides of nitrogen are formed when oxygen and nitrogen react in the heat of car engines. the dangers of this is that it can cause acid rain and respiratory problems
• lots of carbon dioxide from the early atmosphere is now 'locked up' in calcium carbonate rocks because 1. CO2 dissolved in water then formed metal carbonates before sinking to the bottom of the sea and forming sedimentary rock 2. plants absorbed CO2, then animals ate them plants so carbon became incorporated into bones so when animals died and sank to the bottom of the sea, they formed sedimentary rocks
• small quantities of other gases that were present in the early atmosphere were 1. nitrogen 2. water vapour 3. ammonia 4. methane
• recent human activities have increased the amount of methane by rice farming and cattle farming
• life first appeared 2.7 billion years ago and because of this, the level of oxygen in the atmosphere increased due to photosynthesis
• recent human activities increase the amount of carbon dioxide in the atmosphere by burning fossil fuels and deforestation
• the carbon dioxide levels in the atmosphere decrease to today's levels by 1. dissolved in oceans 2. photosynthesis 3. converted to fossil fuels 4. precipitated as insoluble metal carbonates
• three examples of greenhouse gases; 1. carbon dioxide 2. methane 3. water vapour
• oceans formed from water vapour condensing as the earth cooled
• since oxygen levels decreased, this caused the level of ammonia to decrease because it reacted with oxygen to form nitrogen and water
• the early atmosphere was mainly composed of carbon dioxide
• once oxygen levels increased, the level of methane decreased as it reacted with oxygen to form carbon dioxide and water
• possible effects of climate change: 1. sea levels rising 2. extreme weather 3. changes to ecosystems and habitats 4. polar ice caps melting
• water vapour, nitrogen and carbon dioxide originally came from volcanoes
• carbon footprint is the amount of carbon a product, process or person release into the atmosphere over its lifetime
• levels of nitrogen have gradually increased because they were very stable so any process producing nitrogen causes it to build up over time
• carbon monoxide is formed by incomplete combustion and it is dangerous because it is a colourless and odourless toxic gas
• scientists aren't particularly sure about the composition of the earth's early atmosphere because it occurred billions of years ago, so there's little evidence
• particulates are formed by incomplete combustion and the dangers are global dimming and respiratory problems
• the earth's early atmosphere is similar to mars and venus
• sulfur dioxide is formed when sulfur impurities in fossil fuels react with oxygen during combustion and the dangers are acid rain and respiratory problems
• two possible sources of water on earth are condensing water vapour and comets
• the composition of the modern atmosphere is 1. 80% nitrogen 2. 20% oxygen 3. 0.04% carbon dioxide 4. other gases such as argon and water vapour
• global warming is an increase in the overall global average temperature