Hello..
Which four gases did the earth`s atmosphere coantain in the first billion years?
http://www.google.com/#hl=en&tbo=d&spell=1&q=Which+four+gases+did+earth%27s+atmosphere+contained+in+the+first+billion+years%3F&sa=X&ei=M2e2UNiVMJStyAHH3IGIAw&ved=0CC0QBSgA&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.&fp=f53273149085a90d&bpcl=38897761&biw=1366&bih=643
Read widely and take good notes.