The seven earths are those tested with disbelief..... (The Veils and the Lights)

And He, the Exalted, said: {“Say, ‘Be you stones or iron. Or [any] creation of that which is great within your breasts.’ Then they will say, ‘Who will restore us?’ Say, ‘He who created you the first time.’ Then they will nod their heads toward you and say, ‘When is that?’ Say, ‘Perhaps it will be soon.}’” (Al-Isra' 50-51)."

And He, the Exalted, said: “{Have they not considered what things Allah has created? Their shadows incline to the right and to the left, prostrating to Allah, while they are humble.}” (Al-Nahl 48).

And He, Majestic and Glorified is He, said: “{Each one has known its [manner of] prayer and exalting [Him].}” (Al-Nur 41).

Similar to this is what was cited by the Sage (al-Hakim) Muhammad ibn Sinan—peace be upon him—in the book Al-Hujub wa al-Anwar (The Veils and the Lights). The Sage Muhammad ibn Sinan said: I heard the Learned One (al-'Alim) saying: "The seven earths are those who are tested with disbelief; among them are the sincere in disbelief, the specialized in disbelief, the Naqib (Chieftain) in disbelief, the Najib (Noble) in disbelief, the Yatim (Orphan) in disbelief, and the Bab (Gate) in disbelief. Once he has completed that, he is mounted into the metamorphosis (al-masukhiyyah)."

And the Learned One (al-'Alim)—peace be upon him—said: "When the believer completes seven degrees, he becomes one of the angels.