Question: since what has the conference that has the North Texas Mean Green football team been affiliated with the NCAA's Division I?
Context: The 2001 North Texas Mean Green football team represented the University of North Texas in the 2001 NCAA Division I-A football season.  The Mean Green played their home games at the Fouts Field in Denton, Texas, and compete in the newly-formed Sun Belt Conference.  They will be led by fourth-year head coach Darrell Dickey.  They finished the season 5–7, 1–4 in Big West play to finish tied for first place with Middle Tennessee. North Texas Mean Green football program represents University of North Texas in the sport of American football.  The Mean Green compete in the Football Bowl Subdivision (FBS) of the National Collegiate Athletic Association (NCAA) and the West Division of Conference USA (CUSA).  They are coached by Seth Littrell, who started in 2016.  North Texas has produced 24 conference championship titles, with eight postseason bowl appearances and four appearances in the former I-AA (now Football Championship Series) Playoffs.  The Mean Green play their home games at the Apogee Stadium which has a seating capacity of 30,850. The 2011 North Texas Mean Green football team represented the University of North Texas in the 2011 NCAA Division I FBS football season.  The Mean Green were led by first year head coach Dan McCarney and played home games at the new Apogee Stadium in Denton, Texas.  They finished the season with five wins and seven losses and went 4-4 against conference opponents to finish in fifth place in the Sun Belt Conference. The 2016 North Texas Mean Green football team represented University of North Texas in the 2016 NCAA Division I FBS football season.  The Mean Green played their home games at the Apogee Stadium in Denton, Texas, and competed in the West Division of Conference USA (C–USA).  They were led by first-year head coach Seth Littrell.  They finished the season 5–8, 3–5 in C-USA play to finish in fourth place in the West Division.  Because there were not enough 6-win bowl eligible teams, they received a bowl invitation as a 5–7 team with the highest APR score.  They were invited to the Heart of Dallas Bowl where they lost to Army in overtime. The 2012 North Texas Mean Green football team represented the University of North Texas in the 2012 NCAA Division I FBS football season.  It was led by second-year head coach Dan McCarney and played its home games at Apogee Stadium.  It was the Mean Green's 12th and final season as members of the Sun Belt Conference (SBC); the school will join Conference USA on July 1, 2013.  The team finished with a record of four wins and eight losses (4–8 overall, 3–5 in the SBC) to finish seventh in the conference. The Sun Belt Conference is a collegiate athletic conference that has been affiliated with the NCAA's Division I since 1976.  Originally a non-football conference, the Sun Belt began sponsoring football in 2001.  Its football teams participate in the Division I Football Bowl Subdivision (FBS).  The 12 member institutions of the Sun Belt are distributed primarily across the southern United States. The 2014 North Texas Mean Green football team represented the University of North Texas during the 2014 NCAA Division I FBS football season.  The team was led by fourth-year head coach Dan McCarney and played its home games at Apogee Stadium.  It was the Mean Green's second season as members of Conference USA, competing in the West Division.  They finished the season 4–8, 2–6 in C-USA play to finish in fifth place in the West Division. The 2010 North Texas Mean Green football team represented the University of North Texas in the 2010 NCAA Division I FBS football season.  The 2010 season was the team's fourth under head coach Todd Dodge.  The Mean Green played their home games on campus at Fouts Field in Denton, Texas as members of the Sun Belt Conference.  They finished the season 3–9, 3–5 in Sun Belt play. The 2013 North Texas Mean Green football team represented the University of North Texas during the 2013 NCAA Division I FBS football season.  The team was led by third-year head coach Dan McCarney and played its home games at Apogee Stadium.  It was the Mean Green's first season as members of Conference USA, competing in the West Division.  The team earned a 9-4 record (6-2 in conference) and won the 2014 Heart of Dallas Bowl.  Additionally, it set a school record for average home attendance per game at 21,030.  The defense was notable for being statistically the best second half defense in the Football Bowl Subdivision.  It received two top 25 votes in the Coaches' Poll to end the season. The 2009 North Texas Mean Green football team represented the University of North Texas in the 2009 NCAA Division I FBS football season.  The 2009 season was the team's third under head coach Todd Dodge.  The Mean Green played their home games on campus at Fouts Field in Denton, Texas.  North Texas finished the season 2–10 and 1–7 in Sun Belt play.
Answer: since 1976