 Now let's look at mankind's influence on the carbon cycle. Hundreds of millions of years ago huge quantities of living things died and were trapped in layers of rock. These formed our fossil fuels of coal, oil and natural gas. Sometimes they were trapped in mud deposits that got compressed into shale. Tiny pockets of natural gas in these shales are now being exploited by fracturing the deep down rocks in a process called fracking. The carbon dioxide released during respiration is cycled naturally. The same is the case if we burn wood and agricultural waste, even biogas given off from food we throw into rubbish tips and from sewage works. All this carbon has been recently captured from the atmosphere and we are simply returning it to be used again in the natural cycle. However when we burn fossil fuels the carbon in them has been underground for hundreds of millions of years and this adds new carbon dioxide to the atmosphere. You need to view the video on climate change environment 30 to explore the problems this is causing for our planet. Just as we use 90% of our food as a fuel and only 10% for building and repairing our bodies so with fossil fuels 90% are used as fuels and are combusted and only 10% are used to make things such as plastic. See the linked video on the uses of crude oil. If we burn household waste, including plastics, at least the oil has been used once or twice before it gets used as a fuel. Better still is to use the plastic as a resource for making new plastics by recycling. So there it is, the carbon cycle. Remember that carbon dioxide and oxygen dissolve in water so there is a similar cycle that keeps life working in the oceans too. Matter cannot be created so nature continually recycles. It's something that we are relearning to do. See the materials in the recycling video as well.