Effects of Photosynthesis
- Changes to the Earth’s atmosphere, oceans and rock deposition occur due to photosynthesis
- The first life forms emerged around 4 billion years ago
- At the time, there was no oxygen in the atmosphere
- About 3.5 billion years ago photosynthetic prokaryotes became the first organisms to carry out photosynthesis
- This began the release of oxygen into the atmosphere
- Millions of years later algae and plants evolved and also carried out photosynthesis
- Around 2.2 billion years ago, the oxygen concentration in the atmosphere reached 2%
- This is known as the Great Oxidation Event
- Other changes to the Earth occurred due to photosynthesis
- Minerals in the oceans were oxidised
- Photosynthetic bacteria released oxygen into the ocean
- When dissolved iron was oxidised it formed iron oxide which is a red precipitate that lies on the sea bed
- Over time a distinctive rock formation was produced - the banded iron formation. Layers of red iron oxide alternate with other mineral oxides
- Banded iron formations are the most important source of iron ores (and consequently our supply of steel)
- Methane and CO2 levels in the air fell, which resulted in an Ice Age
- Because methane and CO2 are important greenhouse gases
- Minerals in the oceans were oxidised
- By 600 million years ago, life had evolved into large multicellular organisms, many of which were photosynthetic (plants)
- This pushed the oxygen concentration of the air up to 20%, peaking at 35% 300 million years ago
- This contributed to the large size of the animals that roamed the Earth at that time
- The current atmospheric oxygen level is around 21%, due to increased human activity eg. burning of fossil fuels, deforestation which remove oxygen from the atmosphere