For how long has the present-day atmosphere been the norm on Earth?
Around 200 million years
What is our atmosphere mainly comprised of today?
1. 78% nitrogen
2. 21% oxygen
3. Small amounts of other gases, mainly carbon dioxide, noble gases, and water vapour
Describe the landscape of the earth 4.5 billion years ago
Molten - so hot that any atmosphere just 'boiled away' into space.
Eventually it cooled down a bit, and a thin crust formed, but volcanoes kept erupting.
The volcanoes gave out lots of gas.
Oceans formed when water vapour condensed
How do we think the oceans and atmosphere were formed?
From the gas given off by volcanoes
Describe the early atmosphere
1. Mostly CO2
2. Virtually no oxygen
3. Maybe water vapour, methane, and ammonia
What was the Earth's early atmosphere probably similar to?
The atmospheres of Mars and Venus today
What 2 organisms evolved on the Earth?
1. Green plants
They could live in an atmosphere that was mostly CO2
What changes happened to the atmosphere in phase 2?
Became less abundant in CO2, and more abundant in oxygen
What 2 things caused the changes in the Earth's atmosphere in phase 2?
1. A lot of the early CO2 dissolved into the oceans
2. The green plants and algae absorbed some of the CO2 and produced oxygen by photosynthesis
What happened to the early plants and algaes, along with the skeletons and shells of early marine organisms when they died?
1. They were buried under layers of sediment.
2. The carbon and hydrocarbons inside them became 'locked up' in sedimentary rocks as insoluble carbonates (e.g. limestone) and fossil fuels
What happens when we burn fossil fuels today?
The 'locked up' carbon inside them is released and the concentration of CO2 in the atmosphere increases
What 3 things did the build of oxygen in the atmosphere do?
1. Killed off some early organisms that couldn't tolerate it
2. Allowed other more complex organisms to evolve and thrive
3. Created the ozone layer (O3), blocking harmful rays from the Sun and enabling more complex organisms to evolve
How much CO2 is left in the atmosphere now?