From an article from a forum:
The idea that G-d created other worlds than our own is not a new idea. In fact in the Cabalist text Sefer Yetzirah, which in written form is over One thousand years old and orally older than that, spoke of Seven Earths that were created.
From the Sefer Yetzirah:
Seven Double Letters: Beyt b, Gimel g, Dalet d, Kaf k, Pey p, Resh r, Tav t are the foundation. He engraved them, He hewed them out, He combined them, He weighed them, He set them at opposites, and He formed through them: Seven Stars in the universe, Seven Days in the year, Seven Gates in the body of male and female. And from them He engraved seven heavens, and seven earths, and seven Sabbaths. Therefore He cherished the seventh under all the heavens.
The most distant was named Erez, followed by Adamah, then Arka, Harabbah or Ge, Yabbashah or Neshiah, Ziah or Tebel, and our then own world Heled(Though some texts say it is Ziah followed by Tebel which is our world.). It is written they are separated each by Abyss, Chaos, and Waters. This water here is the same type in Genesis which is of the Deep or Tehom, not actual H2O. Its seems to be a decent description of space from something written over a thousand years ago.
Now medieval scholars interpreted the Abyss, Chaos, and Waters separating each world as the destruction of a world laying way for the creation of the next. The problem with that is that its mentioned in relation to the Seven Heavens which according to the writings all coexist. Even more damaging to that interpretation is that in the writings Is that some of these worlds have Humans on them who are the Descendants of Adam.
At least one of the worlds is described as a Desert world with two suns. Neshiah has a red sun and the "people" that live on it arn't human, they are dwarves with no noses. Erez is described as a dark world without light. Another has humans on it who can travel to the other earths, Adam himself according to legend travelled to these other earths after leaving Eden. The closest one to us is said to be inhabited by creatures who are not remotley human. Adamah is inhabited by phantom like beings. Descendants of Cain are said to live on Arka. Ge and Neshiah are both described as having Trees but no wheat or any of the Seven Species, which are seven plants important to Judaism.
Another Cabalistic text the Zohar mentions thousands of worlds in addition to the seven earths. The Zohar is around one thousand years old at least in written form.
At first I thought the idea of Seven Earths was just isolated to Cabalist texts and Jewish legends. I was wrong.
From the Quran "It is Allah Who has created seven heavens, and earths as many ..." Surah 65:12
There are numerous references in Islam to Seven earths. One very interesting quote I found was this. "Under it there is another Earth with a journey of five hundred years between them," and so on till he had counted seven earths with a journey of five hundred years between each pair."
Five hundred years of travel time hmm. Sounds like STL space travel. So the furthest away would be around 3000 years of travel time, then 2500, 2000, 1500, 1000, and finally the closest at 500 years of travel time. Travelling hundreds of years not on but through "Abyssal waters" sounds alot like space travel.
Here's the Seven Earths of Islam. The first is called Remaka . The second is called Khalada. Both are described as hellish. The third is called Arqa, could this be the same as the Jewish Arka which is also the Third furthest away. The fourth is Heraba which is also the same name as the Jewish fourth world. It appears the two groups of Seven Earths are one and the same. The fifth is Maltham. The sixth is Sijjin. The Islamic Seven worlds differ in that their is a seventh Earth thats not our earth, but a world called Ajiba. All of these worlds are described as Hellish places, with mostly inhuman inhabitants.
A number of modern Muslims claim these Seven Earths are actually Seven layers of the Earth and correlate to the Crust, Mantle, Core, etc. Like the odd interpretation of the medieval scholars of the Jewish Seven Earths this has problems too. Namely the whole unearthly waters and the 500 year travels times that separate the worlds.
As I continued my research I found even an even older source: Zoroastrianism. It has a concept called the Hash Kashvare Zamin or the Seven Earths. They are described as being with Avat or non terrestrial.
The seven earths can be found in Midrash Konen. (Good luck trying to find a copy!)
(19) MIDRASH KONEN, or Adonai be-Ḥokhmah Yasad Areẓ, dealing with the Creation, the heavens, paradise, and hell. This Midrash was influenced by apocalyptic sources of the Second Temple period, and by the mystic literature of the beginning of the Middle Ages. Composed not earlier than about the 11th century, it was first published in Venice in 1601. Another version was published from manuscript by A. Jellinek (Beit haMidrash, 5 (1938), 63–69) and excerpts from similar Midrashim, Seder Rabbah di-Vereshit, were published by S.A. Wertheimer (Battei Midrashot, 1 (1950), 1–48). Yet another version, Zeh Ma'aseh Bereshit, appeared in Sefer Razi'el ha-Malakh, and still another version was published from a manuscript by L. Ginzberg (Ginzei Schechter, 1 (1928), 182–7).
See also interesting article: The Two-Headed Gentleman from the World Beneath the Earth