SC21 - Earth and Atmospheric Science ✓ Flashcards
SC21a - What was the likely composition of the earth’s early atmosphere?
Mainly carbon dioxide with small amounts of water vapour with little to no oxygen
SC21a - What was likely responsible for the composition of the earth’s early atmosphere?
- There was lots of volcanic activity in the earth’s early years and so volcanoes probably were a a major part of it
- They release large amounts of carbon dioxide and water vapour and small amounts of other gases (inc. nitrogen)
SC21a - What evidence supports ideas about earth’s early atmosphere?
- Other planets near to earth (i.e. Venus and Mars) are mainly made of carbon dioxide that is thought to be released form volcanoes
- These planets should have a similar atmosphere to what earth was like before humans affected it
SC21a - Why may some scientists think earth’s atmosphere was made up of nitrogen mainly and why was this disregarded?
- Titan, a moon of Saturn is made of of >98% nitrogen
- However, unlike any other planets closer to earth, titan has an icy interior so is less likely to be similar to earth
SC21a - How were the oceans formed?
The earth cooled down and the water vapour condensed forming oceans
SC21a - What evidence supports the claim that the early atmosphere contained little to no oxygen?
- Volcanoes don’t produce oxygen
- Iron pyrite can’t form in the presence of oxygen and it can be found in very ancient rocks
SC21a - How long ago did oxygen levels start to rise and how do we know this?
- About 2.4 billion years ago, iron oxide started to form. Oxygen had to be present for oxidation to occur
- There is fossil evidence of microorganisms that produced this
- Some geologists believe that only after enough oxygen was present to oxidise iron could atmospheric oxygen rise
SC21b - Describe the changes in levels of oxygen and carbon dioxide in the earth’s atmosphere
Oxygen levels increased and carbon dioxide level decreased
SC21b - In what three ways did oceans change the atmospheric composition?
- Water vapour lessened as it formed oceans
- Carbon dioxide dissolved in oceans reducing carbon dioxide in the atmosphere
- Sea creatures used the dissolved carbon dioxide to form shells made of calcium carbonate (limestone) allowing more carbon dioxide to dissolve
SC21b - How did photosynthesis affect atmospheric composition?
Photosynthesis:
Carbon dioxide + Water -> Oxygen + Glucose
This reduced levels of carbon dioxide and increased levels of oxygen
SC21b - How are stromalites formed and how does this show oxygen being produced?
- Cyanobacteria are photosynthetic organisms that produce a sticky mucus
- The mucus traps sand and the organisms need to move above it
- Eventually, these form stromalites
- As stromalites have been around for around 3 billion years this suggests that photosynthesis has been occurring for this long
- Oxygen has been produced by these organisms since then
SC21b - What caused a second jump in the levels of atmospheric oxygen?
Cyanobacteria evolved forming land plants which photosynthesised increasing the levels of oxygen
SC21b - What % of the atmosphere is oxygen?
21%
SC21b - What is the test for oxygen?
In the presence of oxygen, a glowing splint will relight
SC21c - Describe the greenhouse effect
- Energy from the sun is transferred to the earth by (shorter) infrared and light waves
- The earth absorbs some of this, warming up and then emits (longer) infrared waves
- Greenhouse gases in the atmosphere absorb the energy and re-emit it back to the earth
- This causes the temperature of the earth’s atmosphere to increase and is called the greenhouse effect