Earth's boundaries?
D001272:Atmosphere / Q000737:chemistry; D002245:Carbon Dioxide / Q000032:analysis; D018534:Earth, Planet; D004463:Ecology / Q000379:methods*; D017753:Ecosystem; D017752:Greenhouse Effect; D006802:Human Activities; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009584:Nitrogen / Q000378:metabolism; D012623:Seawater / Q000737:chemistry
D002245:Carbon Dioxide; D009584:Nitrogen