Chemistry of the Atmosphere - Y11 Flashcards
For about how many years has the atmosphere reached a composition similar to what it is today? What gases are there in what percentages?
For 200 million years
80% nitrogen
20% oxygen
small proportions of various other gases like co2, water vapour and noble gases (less than 1%)
Why is evidence for the early atmosphere limited?
Because of the time scale of 4.6 billion years
Explain a theory about how the Earth came into existence
- During the first billion yrs of Earth’s existence, there was intense volcanic activity
- This released gases that formed early atmosphere
- and water vapour - condensed to oceans
- atmosphere may have been like atmos in Mars and Venus today
- consisting of mainly co2 with little/no oxygen
What did volcanoes produce? other stuff?
- Nitrogen which gradually built up the atmos.
- Water vapour and CO2
- may have been small prop of methane and ammonia
How were sediments formed on the seabed?
- Lots of CO2 removed from early atmos.
- as it dissolved in the oceans
- dissolved co2 went through a series of reactions to form carbonate precipitates
- that formed sediments
- Reduced co2 in the atmos.
What did the early atmosphere consist of?
- CO2
- virtually no oxygen
- like mars and venus today
How are oceans formed?
- water vapour from atmos. condenses
How did the co2 level slowly decline?
Green plants and algae abosrbed some co2 to photosynthesis which eventually led to more complex life forms
What happend after plants and algae?
Marine animals evolved. Their shells and skeletons contained carbonates from the oceans
What happend to some of the carbon the organisms took in the atmos and oceans?
- Became locked up in rocks and fossil fuels
- after they died
What happens when plants, plankton and marine animals die?
- fall to the seabed
- get buried by layers of sediment
- become compressed over millions of yrs
- form sedimentary rocks, oil and gas
- trapping carbon within them, to keep C level in atmos. reduced
How is crude oil and natural gas formed?
- From deposits of plankton
- FF like these form reservoirs under the seabed when they get trapped in rocks
How is coal formed?
- Sedimentary rock
- From thick plant deposits
How is limestone formed?
- Sedimentary rock
- Made of calcium carbonate deposits from shells/skeletons of marine organims
What evolved first? Algae or green plants?
- Algae - 2.7bn yrs ago
- Over the next bn yrs, green plants also evolved