Explain the Oxygen Increase & Carbon Dioxide Decrease

OXYGEN INCREASE: Believed algae evolved about 2.7 billion years ago, photosynthesised, oxygen in atmosphere increased, enabling animals to evolve CARBON DIOXIDE DECREASE: 1) oceans formed, carbon dioxide dissolved to form soluble carbonate compounds which then precipitated as sedimentary rocks (limestone). 2) absorbed from the oceans into photosynthetic algae and plants. Crude oil and natural gas were formed from simple plants and tiny animals which were living in oceans and lakes 3) Over millions of years, heat and pressure turned the remains of the organisms into crude oil and natural gas 4) Coal is a fossil fuel which was formed from trees which were in dense forests in low-lying wetland areas, floods, buried them away(stopping them from being oxidised), compressed and heated over millions of years.