Complex sentence: The atoll is best known for its role in celebrations surrounding the arrival of the year 2000--a 1995 realignment of the International Date Line made Caroline Island one of the first points of land on Earth to reach January 1,2000 on the calendar.
Split into simpler sentences: The atoll is best known for its role in celebrations surrounding the arrival of the year 2000. A 1995 realignment of the International Date Line made Caroline Island one of the first points of land on Earth to reach January 1,2000 on the calendar.