Complex sentence: That sparsely populated village became active in shipbuilding, seafaring, fishing and lobster fishing, though changed little in its first 70 or so years, until the granite boom "circa" 1870, when quarrying became a major occupation.
Split into simpler sentences: That sparsely populated little village became active in shipbuilding, seafaring, fishing and lobster fishing, though didn't change much in its first 70 or so years. That is, until the granite boom around 1870, when quarrying became a major occupation.