Salaam sister,
From Shariah perspective, it is reported in several hadiths that the Prophet (pbuh) used to prostrate on the ground.
Abu Sa’eed used to relate that he had seen the Prophet prostrating on wet mud, so much so that he could see mud stains on his forehead.
Saheeh Bukhari, Part I, p. 104
The Prophet used to place his forehead on the earth while prostrating.
Saheeh Bukhari, Part 1, p. 97
The Prophet declared that the best place for prostration was the earth, or upon something that grows from the earth.
Kanz-ul-Ummal, Part 4., p. 113
There are many more hadiths and proofs about this. Therefore, the followers of the Jaafari school of thought deem it necessary to perform the sajda on “earth, and on those things which are not edible nor worn, and on things which grow from earth (e.g. wood and leaves of trees)”.