C9- Chemistry Of The Atmosphere Flashcards
The proportion of gases in the atmosphere (4)
For 200 million years it has been the same as today:
• About four-fifths (around 80%) nitrogen
• About one-fifth (around 20%) oxygen
• small proportions of various other gases, including carbon dioxide, water vapour and noble gases
Theories about what was in the Earth’s early atmosphere (2)
- One theory suggests that during the first billion years Earth’s existence there was intense volcanic activity that released gases that formed the early atmosphere and water vapour that condensed to form the oceans
- The atmosphere was mainly made up of carbon dioxide with little or no oxygen gas
How was the atmosphere formed (theory)
• Volcanoes produced nitrogen which gradually built up in the atmosphere and there may have been small proportions of methane and ammonia
How has the atmosphere changed and developed over time (theory)
When the oceans formed carbon dioxide dissolved in the water and carbonates were precipitated producing sediments reducing the amount of carbon dioxide in the atmosphere
How was oxygen produced
- Through algae and plants via photosynthesis
- Algae first produced it about 2.7 billion years ago - soon after it appeared in the atmosphere
- Over the next billion years plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve
Equation for the production of oxygen (photosynthesis) (2)
6CO2 + 6H20 —> C6H12O6 + 6O2
Carbon dioxide + water —(light)> glucose + oxygen
Describe the main changes in the atmosphere over time
- Algae and plants decreased the percentage of carbon dioxide in the atmosphere by photosynthesis
- Carbon dioxide was also decreased by the formation of sedimentary rocks
How were sedimentary rocks formed
When plants, plankton and marine animals die, they fall to the sea bed and get buried by layers of sediment - over millions of years they become compressed and form sedimentary rocks such as limestone
How is coal made
- coal is a sedimentary rock
* it is made from plant deposits
How was crude oil and natural gas formed (2)
- formed from deposits of plankton
* these fossil fuels form reservoirs under the seabed when they get trapped in rocks
How is limestone formed (3)
- Limestone is a sedimentary rock
- Mostly made up of calcium carbonate
- deposits from the shells and skeletons of marine organisms
What do greenhouse gases do
Maintain temperatures on Earth high enough to support life
Examples of greenhouse gases (3)
- Water vapour
- Carbon dioxide
- Methane
Describe the greenhouse effect in terms of the interaction of short and long wavelength radiation with matter (2)
- short wavelengths of visible light from the sun pass through a transparent medium and are absorbed
- but the longer wavelengths of the infrared re-radiation from the heated objects are unable to pass through that medium
State two human activities that increase the amounts of each of the greenhouse gases carbon dioxide and methane
- Burning fossil fuels
* Cutting down forests