What is the composition of earth's atmosphere?

Question

only a few sentences, make it easy for a year 9 student to understand

Answer 1

IIRC it's about 70% nitrogen, 23% oxygen, 6% carbon dioxide, and the remaining 1% are trace gasses such as ozone, argon, neon, etc.

There's just got to be a bunch of places on the web that will have it broken down better. Get on a search engine ☺

Doug

Answer 2

The atmospheric composition on Earth is largely governed by the by-products of the very life that it sustains. Earth's atmosphere consists principally of a roughly 78:20 ratio of nitrogen and oxygen, plus substantial water vapor (a gas), with a minor (but increasing) proportion of carbon dioxide. There are traces of hydrogen, and of argon, helium and other "noble" gases (and of volatile pollutants). Exact measurements are difficult, except for particular locales at a particular time.

Answer 3

Permanent gases: about 21 percent oxygen
about 78 percent nitrogen about 1 percent argon and about 1/30th of 1 percent CO2.
Other gases: Water, up to 4 percent in hot, humid weather, different air pollutants.