Gas bubbles and pollutants buried within layers of antarctic ice are in essence
a. records of earth's air.
b. the main cause of global warming.
c. caused by researchers living there.
d. sources of natural gas.

The Correct answer is A.

As snow becomes compressed , air between the flakes gets trapped. The process involving trapping of air occurs during burial of snow layers and  is generally not complete  until the bubbles are about 60 meters or more below the surface.

Once the bubbles have formed, they act as the time capsules of the atmosphere when they were trapped. By extracting the air from the bubble in ice cores, changes in the past can be studied .

 Studies of these changes show the dramatic increase of  what are called greenhouse gases such as carbon dioxide, caused by human use of fossil fuels, as well as natural changes that accompany glacial climate

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