Praise be to Allah.
Allah, may He be glorified and exalted, says (interpretation of the meaning):
“It is Allah Who has created seven heavens and of the earth the like thereof (i.e. seven). His Command descends between them (heavens and earth), that you may know that Allah has power over all things, and that Allah surrounds (comprehends) all things in (His) Knowledge.”
In this verse Allah, may He be glorified and exalted, tells us that He created seven heavens and seven earths, between which His command descends; this refers to His laws and commandments, and His decrees by which all things are controlled and His signs are made clear, so that His slaves may know that to Him belong the creation and the command, and that He has the utmost wisdom and perfect might; to Him belong the most beautiful names and sublime attributes; not even the weight of an atom (or small ant), in the highest heaven or the lowest earth, is beyond His power and knowledge; and so that they may know that He is able to bring people back to life after they have died, and raise them up and resurrect them from their graves, so that they will love Him and worship Him, and they will be obedient to Him and to His Messengers. This is the purpose for which He created mankind.
Ibn Katheer (may Allah have mercy on him) said:
Allah, may He be exalted, tells us of His perfect might and absolute power, so that this will motivate us to venerate the true religion that He has ordained. Allah says (interpretation of the meaning):
“It is Allah Who has created seven heavens and of the earth the like thereof (i.e. seven).”
End quote from Tafseer Ibn Katheer, 8/156
Ash-Shawkaani (may Allah have mercy on him) said: “and of the earth the like thereof” means, and He created the earth something like them, i.e., seven. There was a difference of opinion concerning the nature of the levels of the earth. Al-Qurtubi said in his Tafseer: They (the scholars) differed concerning them, and there are two opinions. One of them, which is the view of the majority, is that there are seven earths in layers, one above another, and between each two earths there is a distance like that between heaven and earth. Ad-Dahhaak said: They are in layers, one above another, with no gap in between, unlike the heavens. But the former view is more correct, because the reports indicate that.
End quote from Fath al-Qadeer, 5/346
As-Sa‘di (may Allah have mercy on him) said:
Allah, may He be exalted, tells us that He created all of creation, including the seven heavens and all that dwell therein, and the seven earths and all that dwell therein, and whatever is between them, and that He sent down His command, which is the laws and religious rulings that He revealed to His Messengers to remind and exhort His slaves, and His decrees by means of which he controls all of creation. All of that is so that His slaves will know Him and will understand that His power encompasses all things and His Knowledge encompasses all things. Then they will know Him by His holy attributes and beautiful names, and they will worship Him, love Him and fulfil their duties towards Him. This is the purpose behind creation and the command: to know Allah and worship Him. Those of the righteous slaves of Allah who were guided understood this and acted accordingly, but those who wronged themselves turned away from that.
End quote from Tafseer as-Sa‘di, p. 872
At-Tabaraani narrated in al-Mu‘jam al-Kabeer (8987) with a hasan isnaad from Ibn Mas‘ood that he said: The distance between the lowest heaven and the next one is the distance of five hundred years’ travel, and the distance between each heaven and the next is the distance of five hundred years’ travel.
So the heavens are seven, and the earths are seven, and that is by the perfect might of Allah, may He be exalted, and the command and decree of Allah descend between them.
What is required of us is to adhere to what is known from sharee‘ah, and not overstep the mark. The Qur’an and the saheeh Sunnah have told us that there are seven heavens and seven earths.
We know from the Sunnah that each heaven has its inhabitants, but there is nothing that tells us about the earths other than the one in which we live. So what we must do is adhere to what the reports say, and believe that there are seven earths, without seeking to know further, or to find out whether this is proven by modern science or not, or other things that may generate doubt and uncertainty. Rather we must believe that complete knowledge and power over these higher and lower realms belongs to Allah alone. This is part of knowing that He has power over all things, and that He encompasses all things in His knowledge. Nevertheless, we say: We hear, we obey and we believe.
See also the answer to question no. 112059
And Allah knows best.