wa innaa la jaa’iloona maa ‘alayhaa Sa’eedan Juruza
And surely We, surely [will] make what [is] upon it (the Earth) Dust, [and] Lifeless. [al Kahf 18:8]
Sa’eed – Dust.
[similar word; Sa’ood – an Elevated height – (see: Muddathir 74:17)] is also mentioned in the Qur’an.
So right now you see Mountains and Heights of buildings etc. (Sa’ood) However, one day they will all collapse apart and all you will see above you and around you is Dust (sa’eed).
Juruza – Lifeless / dead.
From the word Jarz – to kill off a land so no vegetation grows on it.
I.e.When a land has plants and trees and life, when all that is destroyed and the land is barren/dead = Juruza.
So Allah is telling us through these 2 words that all that is Above you and Below you will become lifeless, dead and only dust / nothingness.
Allah has shown His creative power over the Earth and how He has placed so much life, height and beauty in it. Yet He will cause it all to become lifeless and nothingness.