The answer to the clue has only four letters - just an abbreviation for Earth after an anagram of (crumbling) 'old'. That's probably a huge hint, I can't think of anything subtler!
Stuck on:
20d American tenor that's wearing bronze tight-fitting upper garment. I have B?S???R
29d Nurse with close-cut hair lifting heavy weight . T???E
21d One local copper guarding room helps to remove the mail?