The line stretched forever. people put their bags on the floor and inched them forward. my father and i removed our shoes. there was an announcement about a gate change and a delay on an arrival from chicago.

The above passage states the incident is happening in the security line at an airport.

Explanation:

He says that the queue remained same for long time because the security line in the airport moves very slowly. They have been waiting for a long time, while people put their bags on the floor he removed his shoes along with his father.

And he also states about the information announced regarding the gate change and the delay of flight arrival from Chicago. After few hours of waiting in the airport queue they finally departed.

"the day we found the sharks' teeth" i would say highlight the element of the plot as it sets its boundaries and centers the adventures of them being on a boat and cleaning spit of sand.