Changes which take place and have taken place in the Earth's crust, biosphere and atmosphere are all studied in GCSE Science. This is the last of three quizzes on that topic and it looks in particular at carbon dioxide and the carbon cycle.
The Earth's atmosphere has undergone many dramatic changes since it was formed around four billion years ago - and it is still changing today. It has been much the same for the last 200 million years or so and provides the conditions needed for life as we know it on Earth. Recently, human activities have resulted in further changes in Earth's atmosphere. One of the gases that we send into the atmosphere is carbon dioxide. This is thought by many to be causing changes to the world's climate.
Most of the carbon dioxide we put into the atmosphere comes from burning fuels, making cement and countless other processes that we use to make our everyday products. Most scientists believe that the carbon dioxide produced by humans is causing the Earth to slowly warm up. We call this global warming and it is caused by the greenhouse effect. Carbon dioxide is one of the many greenhouse gases that trap heat in the atmosphere. This slowly raises the average temperature of the planet. If this warming continues, we may eventually reach a point where the effect is not reversible. Temperatures will rise to such an extent that all life on Earth, apart from extremophiles, will become extinct.
Under normal circumstances, there is only a small amount of carbon dioxide in the air. Most is locked away as hydrocarbon molecules in fossil fuels or as the carbonate ion in limestone, chalk and other 'carbonate' rocks. Carbon dioxide is taken from the air by photosynthesis and returned to the air by respiration. But burning large amounts of fossil fuels or making large quantities of cement 'unlocks' the carbon dioxide that was stored away millions of years in the past. This puts extra carbon dioxide into the air and so there is more than can be removed by photosynthesis. The situation is not helped by large scale felling of trees, the largest photosynthesisers, such as is happening in the tropical rainforests.