In cases like this, sometimes it seems that certain words refer to things more important than others, but is explained by the simple use of capital letters in proper nouns.
Alá es el dios de los musulmanes y Dios es el dios de los cristianos.
Lowercase dios refers to some powerful spiritual being.
Uppercase Dios refers to the name given to that spirit in our culture and language, the same way that your name is Clay with a capital.
Tierra is the name of our planet, the same way that Venus. In Spanish, lowercase tierra means land, ground, soil and sometimes dust.
Los cielos is an ancient and poetic way of referring to heaven. Churches give a historical and religious explanation for this plural use of the word, explaining that refers to several entities (states, times, places?). The Jewish tradition recognizes seven heavens, each with its name capitalized of course. Therefore orthographically:
El avión surcó los cielos.
El nombre del primer cielo es Shamayim.