The date of First Contact is one of the most pivotal moments in Star Trek canon, but Star Trek: Enterprise revealed a little-known truth that Vulcans actually landed on Earth in the 1950s, over 200 years before it. Although many aliens have visited Earth before Zephram Cochrane (James Cromwell) met the Vulcans in Star Trek: First Contact, it was meeting the pointy-eared race at a crucial moment in history that launched Earth on its destiny to become a galactic power.
Star Trek history records that Vulcans landed on Earth and made First Contact with humanity on April 5, 2063 after Zephram Cochrane successfully achieved mankind's first warp flight aboard his makeshift starship, the Phoenix — with a lot of help from the time-traveling crew of Captain Jean-Luc Picard's (Patrick Stewart) USS Enterprise-E, which, naturally, isn't in the history books. First Contact Day became one of United Earth's most important holidays, although in Star Trek: Picard's timeline, it took a dark turn as the date of the attack on Mars by rogue synthetics in 2385. Regardless, First Contact with the Vulcans is a sacrosanct moment in time for the human race and it's permanently marked with a statue of Zephram Cochrane at the landing site in Bozeman, Montana that every schoolchild is raised to learn about.
However, much like the secret of the Enterprise-E's role in helping First Contact happen, there's another hidden truth that Subcommander T'Pol (Jolene Blalock) shared with Captain Jonathan Archer (Scott Bakula) and Commander Trip Tucker (Connor Trinneer) in the Star Trek: Enterprise season 2 episode "Carbon Creek." In 2152, T'Pol revealed that her great-great-grandmother, T'Mir, was part of a Vulcan survey mission that crashed on Earth in 1957 after they studied the launch of Sputnik, Earth's first man-made satellite. The Vulcans landed in Carbon Creek, Pennsylvania, and lived there for a few months before they were rescued. Further, one of the Vulcans, Mestral (J. Paul Boehmer), became fascinated with humans and he opted to remain on Earth, presumably until he died, which could have been 100-150 years later. Although T'Pol framed her tale as "a story", which allowed Tucker and Archer to continue to believe in the historical date of First Contact, the NX-01 Enterprise's Science Officer kept T'Mir's purse from Earth as a keepsake, which means her story is true.
While they kept the fact that they were aliens a secret in order to prevent panic or influence the planet's natural progression, the Vulcans in 1957 still altered history in subtle ways. T'Mir frowned upon Mestral becoming friendly with the people of Carbon Creek but she eventually befriended a bright, college-bound teenager named Jack (Hank Harris), who impressed her with his knowledge of science. When T'Mir learned that Jack couldn't afford to go to college, she made a surprising choice to sell the Velcro the Vulcans owned to acquire the money for Jack's education. This means that in Star Trek's canon, it's the Vulcans who secretly gave the human race Velcro! Meanwhile, in the real world, the inventor of Velcro was George Mestral, who the Vulcan in Star Trek: Enterprise is named for, although Velcro was really invented in 1955.
Vulcans are also not the first aliens to visit Earth by any means: Star Trek: The Original Series revealed that numerous extraterrestrials, including Apollo (Michael Forrest) and the other Greek gods, have been to Earth. Guinan (Whoopi Goldberg), an El Aurian, lived in 1893 San Francisco, as did two Dividians, before they were joined by the crew of the Enterprise-D in the Star Trek: The Next Generation episode "Time's Arrow."
Meanwhile, Spock (Leonard Nimoy) actually pre-dated T'Mir's arrival on Earth when he and Captain James T. Kirk (William Shatner) were sent to 1930s New York City by the Guardian of Forever in the TOS classic "The City On The Edge of Forever." Spock's visit to Earth 20 years before T'Mir could technically be considered Vulcan's original First Contact with humanity, and it's also a secret that Star Trek: Enterprise's T'Pol didn't know about.