Can anyone explain it plz​

a class of chiefly marine multicellular algae (division Rhodophyta) comprising algae in which red phycoerythrin and sometimes blue phycocyanin mask the chlorophyll, in which no motile form or stage exists, and in which there is a well-marked and often complex alternation of generations — compare red alga

Explanation:

oxygen = 21% of the atmosphere

nitrogen = 78%

carbon dioxide = 0.1%

argon =0.934%