To illustrate: Imagine living in a densely populated walled city that had no way of importing fresh water or exporting waste products. Such a city would soon become filthy and uninhabitable.
مَعَ ذٰلِكَ ،‏ لَا يَفْرَغُ أَبَدًا غِلَافُنَا ٱلْجَوِّيُّ مِنَ ٱلْأُكْسِجِينِ وَلَا يُصْبِحُ مُثْقَلًا بِثَانِي أُكْسِيدِ ٱلْكَرْبُونِ .‏