Final answer:
Nelson Mandela was born in 1918, which is before the official implementation of apartheid in 1948. Among the options provided, Mandela's birth is the event that happened first.
Step-by-step explanation:
The event in Nelson Mandela's life that happened before the official beginning of apartheid was Nelson Mandela's birth. Mandela was born on July 18, 1918, whereas apartheid was officially implemented by the National Party government in 1948 after they won the elections. Therefore, amongst the options given, Nelson Mandela's birth predates the institutionalization of apartheid and the other listed events such as his imprisonment on Robben Island, Mandela's involvement in the African National Congress (ANC), and the Sharpeville Massacre.