The Earth’s atmosphere has changed drastically over thousands of years and here we’re going to examine the early atmosphere and the presence of carbon dioxide,
The early atmosphere was made up mostly of carbon dioxide, along with smaller amounts of methane, ammonia, nitrogen and water vapour. Around 3.4 billion years ago, organisms similar to bacteria evolved which could break down chemicals around them to provide energy.
Later on, bacteria, algae and plants evolved which could harness the energy of the sun by carrying out a chemical reaction called photosynthesis, which produces oxygen.
The earliest living organism evolved to survive in conditions of little or no oxygen, so the oxygen produced by photosynthesis was toxic to them.
200 million years ago, the atmosphere stabilised and has remained much the same ever since. As well as nitrogen, the atmosphere contains approximately 21% oxygen and small amounts of other gases such as argon (0.9%) and carbon dioxide (0.04%). However, the levels of carbon dioxide are slowly increasing because of the carbon dioxide released upon burning fossil fuels.
Plants containing carbon were then eaten by animals, so the carbon was transferred to animal bone and tissue. As time passed, the dead bodies of these organisms built up at the bottom of the ocean, where they formed calcium carbonate (limestone) rock. Dead organisms which were crushed and heated by the Earth’s crust turned into fossil fuels.
Recently, we have burnt fossil fuels and released carbon dioxide into the air which was previously stored for billions of years – not all of the carbon dioxide can be recycled back into the environment, so carbon dioxide levels in the atmosphere are gradually rising.
As we burn fossil fuels, stored carbon dioxide is released into the atmosphere. The carbon dioxide is absorbed by the ocean. Reactions within the sea make soluble hydrogencarbonates and insoluble carbonates such as calcium carbonate.
Excess dissolved carbon dioxide decreases the pH of the ocean so that it is more acidic – eventually this reaches a level which can kill important marine organisms.
The ocean acts as a buffer because it can absorb this extra carbon dioxide. However the ocean is now struggling to cope with the increasing carbon dioxide levels – some coral reefs are starting to die because the carbon dioxide makes the water too acidic.