Vials of Moon dust brought back to Earth by Armstrong and Buzz Aldrin were found last month by an archivist while tidying up a storage space at the Lawrence Berkeley National Laboratory.
"We don't know how or when they ended up in storage," Karen Nelson, who made the surprising discovery, said in a statement from the lab.
When Apollo 11 returned from its historic flight in 1969, the Moon rocks and lunar soil collected by Armstrong and Aldrin eventually found their way to some 150 laboratories worldwide.
One of those was the Space Sciences Laboratory in Latimer Hall on the UC Berkeley campus. After experiments were conducted and papers published, those samples should have been sent back to NASA.
Instead they wound up in storage, where they sat collecting dust until they were discovered more than four decades later.
Nelson uncovered the Moon dust - about 20 vials with handwritten labels and dated "24 July 1970" - last month while reviewing and clearing out artefacts from the lab's warehouse.
"They were vacuum sealed in a glass jar," said Nelson, who has worked in Berkeley Lab's Archives and Records Office for 17 years.
Along with the jar was a copy of the paper "Study of carbon compounds in Apollo 11 and Apollo 12 returned lunar samples," published in the Proceedings of the Second Lunar Science Conference in 1971.
Among the five co-authors, all from the Space Sciences Laboratory is Melvin Calvin, who was also an associate director of Berkeley Lab and 1961 winner of the Nobel Prize in Chemistry.
The paper examined the nature and chemical characteristics of the carbon in the lunar samples.
Nelson contacted the Space Sciences Laboratory.
"They were surprised we had the samples," she said. She then contacted NASA, who asked that the samples be sent back but allowed her to first open the jar to remove the vials. PTI SAR AKJ