Unit 9 GCSE Chemistry

Earths early atmosphere

The earth was formed 4.6 billion years ago. One theory suggests that the early atmosphere came from intense volcanic activity. The atmosphere had a large amount of carbon dioxide, little or no oxygen and small amounts of other gases such as ammonia or methane. Volcanic activity also released water vapour which condensed when the earth cooled to form the ocean. Nitrogen was also released by volcanoes but due to being unreactive built up in the atmosphere.  

How oxygen increased

Plants make their own food via photosynthesis (carbon dioxide+water=oxygen+glucose) scientists believe algae evolved 2.7 billion years ago which built up the level of oxygen in the atmosphere eventually allowing animals to evolve 

How carbon dioxide decreased

carbon dioxide is a very soluble gas that dissolves readily in water, as the oceans formed  carbon dioxide dissolved and  formed soluble carbonate compounds meaning the amount in the atmosphere decreased. carbonate compounds were then precipitated as sedimentary rocks such as limestone  carbon dioxide was also absorbed from the oceans into photosynthetic algae and plants, many of these would be turned into fossil fuels (coal, natural gas and crude oil) 

Coal

Coal is a fossil fuel that is formed from trees in dense forest that had low lying wet areas. floods would collapse the trees and bury them in a way were oxidation is not possible. compression and heating over millions of years turns the wood into coal

Crude oil and natural gas

Crude oil and natural gas are also fossil fuels . they are formed when tiny animals and plants that are in the ocean die they go to the bottom of the ocean and are covered with sediments the lack of oxygen prevents oxidation occuring over millions of years heat and pressure turns the remains of the organisms into crude oil and natural gas 

Greenhouse gases

Greenhouse gases are gases in the atmosphere that retain heat from the sun in the atmosphere. the 3 main ones present in our atmosphere are: methane, carbon dioxide and water vapour. The sun radiates short wavelength infrared radiation at the earth some of this is absorbed and some the earth relfects. greenhouse gases however retain the heat the earth sends back in the atmosphere causing the temperature of the earth to rise-the greenhouse effect.  

Human activities+the greenhouse effect

Farming cattle and rice releases methane into the atmosphere. Burning fossil fuels in cars and power stations releases carbon dioxide in the atmosphere. Deforestation increases the amount of carbon dioxide in the atmosphere and decreases the amount that is taken out of the atmosphere via photosynthesis 

Climate change

Climate change is the change in the average global temperature of earth. climate change is an effect of global warming. Some other effects of Global warming include: glaciers and polar ice caps melting, sea levels rising