How does the author show us some time has passed since the end of Chapter 2?

The author shows us that time has passed between the second and third chapter in the way he describes Jack's appearance.

His sandy hair, considerably longer than it had been when they dropped in, was lighter now; and his bare back was a mass of dark freckles and peeling sunburn. A sharpened stick about five feet long trailed from his right hand, and except for a pair of tattered shorts held up by his knife-belt he was naked.