영어 문장에서 since가 쓰인 이유가 궁금해요

“It’s a significant find, since that part of the jetliner holds the black box and flight data recorders which will help officials find out why the plane crashed.”
“Since day one, forty bodies have been recovered out of the one hundred sixty-two people who were on board.”
두 문장에서 since가 어떤 의미와 문법으로 쓰였는지 설명 부탁드려요.