You’ll be surprised…
In the old testament – and to date in Judaism – Heaven is called the Garden of Eden and its exact location is given in the book of Genesis 2:10: between the rivers Pishon, Gihon, Tigris, and the Euphrates. While the location of the first two was lost in time, the Tigris and Euphrates still flow in modern-day Iraq.
In ancient Judaism, God’s reward for being righteous was not in the afterlife, but in this life; So it made perfect sense that heaven will be a place on earth.
This theological concept changed during the miserable years of the Persian and Greek occupation of Hollyland when all the Israelites – even the righteous ones – suffered severely. In those years, it did not sit well with reality, hence heaven ascended to the skies and the righteous’ reward was postponed to the afterlife…. kind of a rain check.
The first written assertion that heaven is NOT a place on earth, but in the skies, is in the book of Enoch which older sections are, indeed, estimated to date from the time of Greek occupation of ancient Israel.
However, the concept of heaven in the skies is – and apparently always was – a part of the theological Christian dogma as well as the Islamic dogma.