A look at the NFL's sixth decade, the 1970s:
FRANCHISES: The NFL's final and biggest merger kicked the league into a new era in 1970, the start of a decade where pro football entered the modern era. Combining the AFL and NFL meant splitting 26 teams into two conferences.
Baltimore, Buffalo, Cincinnati, Cleveland, Denver, Houston, Kansas City, Miami, New England, New York Jets, Oakland, Pittsburgh and San Diego went to the new American Football Conference.
The National Football Conference featured Atlanta, Chicago, Dallas, Detroit, Green Bay, Los Angeles Rams, Minnesota, New Orleans, New York Giants, Philadelphia, San Francisco, St. Louis Cardinals and Washington.
The NFL expanded to 28 teams in 1974 with Seattle and Tampa Bay starting play in 1976.
Miami: Three straight Super Bowl berths, two titles and a perfect 17-0 season in 1972.
Pittsburgh: NFL's first team to win three Super Bowl championships.
Dallas: Won two Super Bowls, lost two more — both to Pittsburgh.
O.J. Simpson, Buffalo. The former Heisman Trophy winner from Southern Cal became the first player in NFL history to run for more than 2,000 yards in a season in 1973, finishing with 2,003 yards.
Bob Griese, Miami. The quarterback led the Dolphins to three AFC titles and two Super Bowl victories.
Roger Staubach, Dallas. The two-time Super Bowl winner and a Super Bowl MVP led the NFL in passing four times, and the man coined the phrase "Hail Mary" for a desperation pass.
Walter Payton, Chicago. Sweetness ran for 275 yards on Nov. 20, 1977, then a single-game record.
Terry Bradshaw, Joe Greene, Jack Ham, Lynn Swan of Pittsburgh. All Hall of Famers for their roles in the Steelers' dominating run.
Alan Page, Minnesota. The future Minnesota Supreme Court justice was a member of the Purple People Eaters. Page was only the second defensive player named the NFL's MVP in 1971 and a two-time Defensive Player of the Year who had 173 sacks and played 238 straight games.
Ken Stabler, Oakland. His "Snake" nickname alone would've been enough, but the left-handed quarterback also was a two-time NFL MVP and a member of the All-Decade Team of the 1970s.
Earl Campbell of Houston. The NFL's MVP and Rookie of the Year in 1978, he won the first of his four league rushing titles. His best season came in 1980 with 1,934 yards, and he finished with 9,407 yards rushing and 74 touchdowns in eight seasons.
Tom Landry: Took Dallas to five Super Bowls in this decade winning two titles and losing three others by a combined 11 points. Landry also coached the first wild-card team to reach a Super Bowl in January 1976.
Chuck Noll: Turned the Steelers into one of the best teams of all-time as the NFL's first to win three Super Bowl titles with a Steel Curtin defense that sent four players to the Pro Football Hall of Fame.
Don Shula: Led Miami to the NFL's first undefeated regular season and finished off the only perfect season at 17-0 on Jan. 14, 1973. He also led the Dolphins to a second straight Super Bowl title.
The Immaculate Reception: If not for Franco Harris scooping the ball up before hitting the turf at Three Rivers Stadium, the Steelers' run to three Super Bowl championships might've been delayed a year. Instead, he helped Pittsburgh beat the Oakland Raiders 13-7 for the Steelers' first win in the playoffs on Dec. 23, 1972.
Sea of Hands: The Raiders ended Miami's run of consecutive Super Bowl berths at three straight Dec. 21, 1974, with a playoff victory in Oakland. Stabler was being pulled down by Vern Den Herder when he shoved the ball toward the end zone where Clarence Davis grabbed the ball away from a pair of Dolphins defenders for the game-winning TD.
The Hail Mary: Last gasp throws had been called a "Hail Mary" try before Dec. 28, 1975. But Staubach finding Drew Pearson for a 50-yard TD pass to beat the Vikings in Minnesota branded such throws when Staubach explained his game-winning throw by saying, "I closed my eyes and said a Hail Mary."
Ghost to the Post: The Raiders and Baltimore Colts played into double overtime of their AFC divisional playoff game on Dec. 24, 1977. Oakland won 37-31 only after Dave Casper caught a 42-yard pass from Stabler to set up the tying field goal late in regulation, and the tight end also caught a 10-yard TD pass for the victory in the fifth-longest game in NFL history.
Super Bowl Goes Indoors: The 1978 Super Bowl marked more than just Dallas' second championship under Landry. The NFL took its marquee game indoors for the first time at the Louisiana Superdome in New Orleans on Jan. 15. Now the only way to play a Super Bowl away from a warm climate is with a roof over the field.
All Together: Names went on the back of jerseys, and the point after touchdown changed to one point. In 1972, owners decided to start counting tie games as a half-game won and lost. The NFL agreed in 1973 to use a uniform numbering system for jerseys limiting groups of numbers to different positions. Division winners started earning home-field advantage in the playoffs in 1975, the same year referees got wireless microphones. The head slap was outlawed in 1977.
Bigger season: The preseason went from six games to four with two games tacked onto the regular season for the 1978 season. A second wild-card team also was added to the postseason.
Football abroad: Long before London, the NFL tested its popularity outside North America on Aug. 16, 1976, when the then-St. Louis Cardinals beat San Diego 20-10 in an exhibition in Tokyo.
TV time: Congress started testing the blackout rule in 1973, requiring a sellout 72 hours before kickoff for teams to show games in local markets. The rule lasted until September 2014.
Commissioner Pete Rozelle negotiated the largest television package to date in 1977, making deals with all three networks for every regular season and playoff game for four years starting in 1978. ABC got the rights to 16 Monday night games, CBS got NFC games and the playoffs, while NBC got the AFC with the networks alternating Super Bowls.
And instant replay made its debut in 1978 with the NFL studying how to help officials during seven preseason games.
Follow Teresa M. Walker at https://twitter.com/TeresaMWalker