the atmosphere

The proportions of different gases in the atmosphere

● For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today: 

o ~4/5 (80%) nitrogen

o ~1/5 (20%) oxygen o Small proportions of various other gases, i.e. CO2 , H2O(g) and noble gases

● ∼ means around/approximately

The Earth's early atmosphere

● Evidence is limited because of the time scale of 4.6 billion years and theories have changed/developed over time

● One theory suggests that during the first billion years of the Earth’s existence… o There was intense volcanic activity that released gases that formed the early atmosphere

▪ At the start of this period, the atmosphere may have been like the atmospheres of Mars and Venus…