1. Ozone

6. Relationship between changes in oxygen concentration and the development of the ozone layer
3500mya Cyanobacteria (photosynthetic) began producing molecular oxygen.
Cyanobacteria
= Oxygen

7. Up until about 2000mya the oxygen was used up in precipitating sediment. Evidence for this are Banded Iron Formations (BIF). This process stopped around 1700mya

8. From about 2000mya oxygen began to accumulate in the atmosphere
From about 2000mya oxygen began to accumulate in the atmosphere. It was only when oxygen levels reached high enough levels that ozone could start to be produced

9. The amount of ozone built up over time to form a thin layer that protected the Earths surface from harmful UV radiation from the sun. Ozone absorbs UV light of certain frequency.

10. This shield allowed for the emergence of aerobic life forms during the Proterozoic and the production of an ozone layer allowed for the emergence of life forms onto land at the end of the Phanerozoic