All have things to do with the middle of the Earth. Melkor was legitimately in charge of heats and frosts (lava, ice etc) and Aule shaped Arda's rock himself. Most of what we 'know' comes from the Elves and Men, who live underground. Perhaps the Dwarves know what is down there, but the lore of LoTR only extends to what Gimli tells Legolas. Not being a Morian, Gimli might not know himself. The knowledge is 'lost' as it were.

Sauron was an Aulean and later Melkorian Maiar, but his service to Morgoth was more of a spy within the Valar's ranks, and even Manwe's (Eonwe considers him one of HIS order) and thus wasn't actually involved in the making of Arda. Come to think of it, most of the Maiar had nothing to do with the making of Arda but rather its management and peoples. Olorin hung around the Elves, Osse ravaged the seas and Melian sat in her forest and sang. The creatures they know live above ground and in the sea/air.

What goes on underground,though , no Elf knows. The Elves always like the singing, dancing,fighting kind of stories. Not tales of mean monsters digging through the world. Maybe if we ask Mr Durin, he might know.

There is but one task remaining in Arda-we,the Dragons of Valinor will make it happen.

Lone resident of the Republic of Gondor

PO-TA-TOE-S not PO -TAH-TOE-S!