chemistry atomsphere Flashcards
1
Q
what 4 gases are in the earths atmosphere today?
NOAC
A
- Nitrogen
- oxygen
- argon
- carbon dioxide
2
Q
what is the percentage of oxygen is in our atmosphere today?
A
21%
3
Q
what was the percentage of oxygen 4 billion years ago?
A
0%
it was mainly carbon dioxide
4
Q
how did the atmosphere change over the first billion years? (4 billion - 3 billion)
(a)
A
CO2 is reduced by algae which photosynthesises. plants give out oxygen.
gases react with oxygen to make nitrogen.
5
Q
balanced equation for photosynthesis
666
A
6co2 + 6h2o —> c6h12o6 + 6o2
6
Q
name another reason why CO2 has decreased?
rocks
A
carbon has been locked up in rocks like limestone and fossil fuels like coal.
7
Q
what is the main compound in limestone?
cc
A
calcium carbonate
