Question: Strikeforce: Shamrock vs. Gracie is notable for featuring the MMA debut of a martial artist born in which year ?
Context: The year 2006 is the 1st year in the history of Strikeforce, a mixed martial arts promotion based in the United States.  In 2006 Strikeforce held 4 events beginning with, "Strikeforce: Shamrock vs. Gracie". The year 2009 is the 4th year in the history of Strikeforce, a mixed martial arts promotion based in the United States.  In 2009 Strikeforce held 10 events beginning with, "Strikeforce: Shamrock vs. Diaz". Strikeforce: Shamrock vs. Baroni was a mixed martial arts event co-promoted by Strikeforce and EliteXC.  The event took place on Friday, June 22, 2007 at the HP Pavilion in San Jose, California.  The main card aired on pay-per-view, with the undercard streamed live on ProElite.com.  The PPV event was rebroadcast on the Showtime premium cable channel on June 30, 2007. Strikeforce: Shamrock vs. Diaz was a mixed martial arts event held by Strikeforce on April 11, 2009 at the HP Pavilion in San Jose, California.  It was the first event promoted by Strikeforce after their acquisition of assets from the defunct EliteXC promotion through its parent company ProElite.  It aired on the Showtime cable network and online through "Strikeforce All Access". Alexander Trevino (born 1981) is an American mixed martial artist, who is best known for his 4-fight stint with now-defunct promotion, Strikeforce.  He was cast a member of former UFC champion, Frank Shamrock's reality series, "School of Hard Knocks” and was part of the Shamrock Submission fighting team until December 2009, and is now part of the Gracie Fighter MMA fighting team. Daniel Jeffery Henderson (born August 24, 1970) is an American former mixed martial artist and Olympic wrestler, who last competed as a middleweight in the Ultimate Fighting Championship.  He was the last Strikeforce Light Heavyweight Champion and was the last Welterweight (80 kg ) and Middleweight (95 kg ) champion of Pride Fighting Championships.  Additionally, Henderson was the Brazil Open '97 Tournament Champion, the UFC 17 Middleweight Tournament Champion, the Rings: King of Kings 1999 Tournament Champion and the Pride Weltwerweight Grand Prix Tournament Champion.  During his career, Henderson also challenged for the UFC Middleweight Championship (2x), the UFC Light Heavyweight Championship and the Strikeforce Middleweight Championship.  He was the first mixed martial artist to concurrently hold two titles in two different weight classes in a major MMA promotion.  At the time of his retirement after UFC 204, he was the oldest fighter on the UFC roster.  Known to be one of the greatest mixed martial artists of all time having defeated a total of seventeen MMA world champions across four major MMA promotions (UFC, PRIDE FC, Strikeforce, and RINGS). Strikeforce: Shamrock vs. Gracie was the inaugural mixed martial arts event promoted by Strikeforce.  The event took place at the HP Pavilion at San Jose in San Jose, California on March 10, 2006.  The main event was the long awaited match between Frank Shamrock, returning to the sport after a 3-year absence, and Cesar Gracie.  The show is also notable for featuring the MMA debut of Cung Le. Strikeforce: Shamrock vs. Le was a mixed martial arts event co-promoted by Strikeforce and EliteXC.  The event took place on Saturday, March 29, 2008 at the HP Pavilion in San Jose, California. Renzo Gracie ( ; ] ; born March 11, 1967) is a Brazilian mixed martial artist and Brazilian Jiu-Jitsu practitioner.  A member of the Gracie family of Brazil, Renzo is a 6th Degree Black in Brazilian Jiu-Jitsu under Carlos Gracie Jr..  He is the son of Robson Gracie, grandson of Carlos Gracie, nephew of Carlos Gracie, Jr. grandnephew of Helio Gracie, and the 1st cousin once removed of Royce Gracie.  In mixed martial arts, Renzo has competed in the Ultimate Fighting Championship, Pride Fighting Championships, K-1, RINGS, and International Fight League (head-coaching the New York Pitbulls).  He holds notable victories over five former UFC Champions: Frank Shamrock (UFC Light Heavyweight Champion), Carlos Newton (UFC Welterweight Champion), Pat Miletich (UFC Welterweight Champion), Maurice Smith (UFC Heavyweight Champion), and Oleg Taktarov (UFC 6 Tournament Winner) Cung Le (Vietnamese: "Lê Cung" ; born May 25, 1972) is a Vietnamese-born American actor, retired mixed martial artist and Sanshou kickboxer.  He competed as a middleweight in the Ultimate Fighting Championship (UFC), holding a record of 2–2 with the organization.  In Sanshou, he is a former International Kickboxing Federation Light Heavyweight World Champion, having a professional Sanshou record of 16–0 before moving to mixed martial arts (Le also held a kickboxing record of 17–0).  He defeated Frank Shamrock to become the second Strikeforce Middleweight Champion before vacating the title to further pursue his acting career.  Le is perhaps best known in mixed martial arts for competing in Strikeforce, holding a record of 7–1 with the organization before its demise.
Answer: 1972