T-Mar would probably want you to start by determining the age by checking component codes on
www.vintage-trek.com. I found a 1983 couple years ago that had chrome moly tubing, NISI alloy rims, six speed freewheel, and a cool head badge with an eagle behind a red "M". Between what T-Mar told me, and the shop owner who sold the bike originally told me, Marina was above the Sports and one or two other models that year.
From what T-Mar told me, this model's position in the heirarchy varied a bit from year to year. Mine (which I sold because it was 66cm) would have been considered an entry-level bike that was a butted tube-set and a component or two away from being a mid-level bike.