Answer
$35000$ years
Work Step by Step
According to the graph, each small box on the x-axis is equal to 10,000 years.
According to the same graph, one complete oscillation of the function is completed in 3.5 squares. Since the period is the time taken for the function to complete one whole oscillation, the period of the function in this question is:
$3.5\times10,000=35000$ years