1. 1) What is the approximate percentage of oxygen in Earth’s modern day atmosphere?.
Answer
21 %

2. 2) Which gas has the largest percentage in Earth’s modern day atmosphere?
Answer
Nitrogen

3. 3) Which gas made up the majority of the Earth’s early atmosphere?
Answer
Carbon dioxide

4. 4) Where is much of the gas that once made up the Earth’s early atmosphere now located?
Answer.
It dissolved in oceans and was then taken up by marine organisms.

5. 5) What is the approximate percentage of carbon dioxide currently found in the atmosphere?
Answer.
0.04 %

6. Answer 6) Give three ways humans have contributed to the amount of CO2
in the atmosphere
Answer
deforestation
burning fossil fuels
farming

7. 7) Which of the following activities is not a human activity that causes small changes to the atmosphere over time?
deforestation
burning fossil fuels
volcanoes erupting
farming
Answer
C) volcanoes erupting

8. 8) Which process was responsible for increasing the amount of oxygen in the atmosphere over time?
Answer
photosynthesis

9. 9) Which gas do plants take out of the atmosphere?
carbon dioxide

10. d) carbon dioxide and steam
10) Which of the following gases are released by volcanoes?
oxygen and nitrogen
carbon dioxide and hydrogen
oxygen only
carbon dioxide and steam
Answer
d) carbon dioxide and steam

11. 11) Which of the following gases could be released when fossil fuels are burned?
carbon dioxide and carbon monoxide
carbon dioxide and oxygen
ammonia and nitrogen
nitrogen and oxygen
Answer
a) carbon dioxide and carbon monoxide

12. 12) How were oceans formed? (3)
Answer
Water vapour released from volcanoes
Water vapour condensed as the earth cooled.
Rain falls to fill up the hollows in the crust.

13. 13) Describe why burning fossil is harmful to the earth and its environment (2).
Answer
Increases amount of CO2 in the atmosphere,;
carbon dioxide is a green house gas, which causes global warming;
greenhouse gases prevent heat from leaving the earths atmosphere;
Trapped heat causes the earth temperature to rise. .

14. 14) Billions of years ago, which gas was in the greatest amount?
Answer
Carbon dioxide

15. 15) Give the origins of one piece of evidence that scientist have collected to explain the composition of the earths atmosphere
Answer
Antarctic ice cores-difference layers contain different amount of each gas. Each layer represents a different time. or
Oxygen locked in rocks.

16. 16) In todays atmosphere, which gas is present that was either in very small amounts or not at all?
Answer
Oxygen

17. 17) Explain how the levels of oxygen has changed over billions of years (2).
Answer
Primitive green plants evolved using carbon dioxide (1)
and released oxygen by photosynthesis (1).

18. 18) Describe how carbon gets locked into sedimentary rocks (2).
Answer
Carbon dioxide dissolved in sea water reacts with other chemicals to form calcium carbonate and calcium hydrogen carbonate (1).
The shells of dead sea creatures accumulate and are transformed into sedimentary rocks (1) .

19. 19) Describe how the levels of carbon dioxide in the atmosphere in the earths early atmosphere was reduced(2).
Answer
By photosynthesis (1) and by dissolving in the oceans (1) .

20. 20) Name three ways humans are changing the atmosphere.
Answer
Burning of fossil fuels
deforestation
livestock farming

21. 21) Answer Iron reacts with oxygen to from iron oxide.
79 mm
iron
100 mm
Explain how the above experiment could be used to determine the amount of oxygen in the atmosphere (4 marks)
Answer
Iron reacts with oxygen to from iron oxide.
Reaction uses up oxygen and total amount of air reduces.
The water rises inside the tube to
fill up the gap

22. Answer 300 x 0.21=63 mm (1) 300-63= 237mm (2) 20) 22) ? mm 300 mm iron
If the atmosphere contains 21 % oxygen, what will the final reading be.
Show your working out. (3 marks)
Answer
300 x 0.21=63 mm (1)
300-63= 237mm (2)

23. 20)
23)
592 mm
iron
750 mm
Show that the percentage of oxygen in the atmosphere is 21 %.
Answer
=158 (1)
158/750= 0.21 (1)
0.21 x 100 = 21 %

24. 24) Answer Copper reacts with oxygen to from copper oxide.
Explain how the above experiment could be used to determine the amount of oxygen in the atmosphere (4 marks)
Answer
Copper reacts with oxygen to from copper oxide.
Reaction uses up oxygen and total amount of air reduces.
The gap between the syringes should reduce.
Compare reading before heating with after heating.

25. Iron + Oxygen ---- Iron Oxide
25)
Iron reacts with oxygen to produce iron oxide. Write the word equations.
Answer
Iron + Oxygen ---- Iron Oxide