Question

2. which of the following statements accurately explains how earths atmosphere supports life?

1.earths atmosphere contains 78 percent oxygen , which is essential for life

2 . earths atmosphere contains 21 percent oxygen , which many life forms need to survive

3. earths atmosphere contains more oxygen than carbon dioxide

4 earths atmosphere contains dioxide , which all life forms breathe in

Answer 1

2. 3. 4. is your right answer.
2 is right, b/c I also read that oxygen in earth's atmosphere is around 20%, not sure how the test done.
3. I read from a textbook.
4. Earth atmosphere contains carbon dioxide, which all life forms breathe in. The atmosphere also contains oxygen, nitrogen, helium, and few others which I forgot. When someone breathes, you never breathe pure oxygen. In fact, if someone constantly breathes only pure oxygen, they die.

Answer 2

I guess, this is my answer, my hypothesis. ^^ You can judge for yourself.

Answer 3

I'm not clear about what you mean for 4. Dioxides are molecules that contain 2 oxygen. I don't think they are necessary for life through breathing in(of course carbon dioxide is important for plants). I might go for 2 and 3.