Update: Wow... That was a complete bust. Went to the neighbors house (as agreed 2 days ago), and I showed up to a frustrated lady who couldn't find the other earring! So... no way to test it against the AT Pro, and whether or not I could even detect it. She rode with me over to the park and showed me where she thought she might have lost it... it was a 30 yard swath probably 700 yards long. AND... she lost it 6 years ago... ouch.
I gave it my level best and for about 3 hours I slow searched that swath... I had to dig EVERY little signal, because I didn't know what I should be looking for. I'm so glad the field wasn't trashy... As it was, I still pulled about $1.80 in change for my efforts, but there was NO earring recovered.
I also got to thinking "have I EVER found an earring that small?" Twice. Once because it was sitting next to a penny, and once because it was a GIANT stud earring at the surface of the sand (in Florida).
I'll have to send her a message, but given the depth of the coins I was finding (it's a WELL watered field), and how "loamy" that soil was... I'm thinking that earring has dropped beyond any hope of me finding it with AT Pro.
Ah well. At least I had great pizza tonight when I got home. (how's that for a random save.)
Skippy