12. What are the main
constituents of the earth's
atmosphere in our time?

Gap-fill exercise

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
The present atmosphere of earth is
constituted mainly molecular nitrogen
(N2) and oxygen (O2).
Nitrogen is most abundant gas,
approximately % of the total volume.
makes up about 20%.
gases exist in the in a low
percentage. ( great concern is the
in the amount of
dioxide due to human , the cause
of the global warming.)