Atholton High School in Columbia was evacuated Thursday afternoon after the school received a bomb threat on the building, according to an email distributed by the school.Howard County Police spokeswoman Sherry Llewellyn said a bomb threat was sent to a school administrator's email account during school dismissal. Atholton's dismissal time is 2:10 p.m.Schools spokeswoman Rebecca Amani-Dove said at 5 p.m. the police had concluded their search of the school and the threat was "unfounded."In an email sent to parents about 3:20 p.m., the school said they evacuated the building "in the name of caution."Police said after the dismissal was completed, a bomb-sniffing dog searched the school.All after-school and evening activities were canceled, the school said. That included boys and girls basketball practice. The girls begin playoffs on Friday; boys playoffs start on Tuesday.Ellen Makar, Atholton PTSA president, said the school's multi-cultural night — an event planned entirely by students — was also scheduled for Thursday, but had to be rescheduled.In a second email to parents at 5 p.m., the school said the building would remain closed tonight, but would be open as usual on Friday, Feb. 22."We took steps to evaluate the threat and concluded the building is safe," the email read. "We continue to remain vigilant in our efforts to ensure safety at Atholton High."Makar said she felt the school took appropriate action in evacuating the building and cancelling after-school activities. All in all, Atholton is a safe school, she said."I know they have protocols in place," she said. "I think they knew exactly what to do and they did it."After speaking with other parents and Atholton principal Jennifer Clements, Makar said that a bomb threat has never happened at Atholton in "anyone's recent memory," and it seemed to be "an isolated incident in the county."