Port Lincoln High School has solved the mystery of when a time capsule was buried on school grounds, set to be opened for its centenary in 2023.
The school put the call out to social media to find the origin of a capsule under bricks at the entrance to its school hall.
School promotions officer Shaun Thomas said after being "inundated" with responses the capsule's installation date was identified as October 8, 1988.
"At last count, well over 5000 people had read our previous Facebook post about the time capsule," he said.
"As several people pointed out, the time capsule was placed inside the bricks adjacent to the entrance to the PLHS Hall on October 8, 1988.
"Many thanks to the dozens of school and wider community members who responded to our request for more information, particularly about the timing of the event, we received dozens of phone calls and Facebook messages."
Mr Thomas said excerpts from the high school's 1988 school magazine show the time capsule was placed in 1988 during the nation's bicenntenial year and the school even spoke to John Scheepers, who was a school groundsman and said he dug the hole the capsule went into.
Other years that were investigated were 1975, when the school's red buildings were built and 1998 when the school celebrated its 75th anniversary but these were dismissed.
Mr Thomas said the school intended to open the time capsule in 2023 to celebrate the school's centenary.
"Given the overwhelming response that we received on this occasion, we look forward to plenty of community involvement in 2023," he said.