I have been doing some research on the Question of other civilisations other than our current one, and even on other planets, this is what I have found so far from Islamic sources.
I hope to add more interesting bits of information as I come across them.
Imam al-Baqir (AS) said,
‘Perhaps you think that Allah has only created this single world, and you think that Allah has not created anyone other than yourselves! Nay by Allah, verily Allah has created a million worlds and a million Adams and you are in the last of these worlds and of the last Adams.’
الإمامُ الباقرُ (عَلَيهِ الّسَلامُ) : لَعلّكَ تَرى أنَّ اللّهَ إنّما خَلقَ هذا العالَمَ الواحِدَ ، وتَرى أنَّ اللّهَ لَم يَخْلُقْ بَشَر غَيرَكُم ! بلى واللّهِ ، لَقد خَلقَ اللّهُ ألفَ ألفِ عالَمٍ ، وألْفَ ألفِ آدمَ ، أنتَ في آخِرِ تِلكَ العوالِمِ واُولئكَ الآدَمِيّينَ
al – Tawhid, p. 277. no. 2
“You may assume that God has not created any humans other than you, but this is not true because he has created thousands of thousands of humans before you and you are the last generation of humans” – Imam Sadiq as
Sheikh Saduq, Tawhid, vol. 2, pg. 277.