At 55, Mr. Middleton is on the older end of his adventure group's age span.

WSJ: The Push for Weekend 'Epics' on the Mountain

Sustained and reinforcing education is needed to effectively encourage people across the age span to take steps to reduce their risk for infection.

WHITEHOUSE: National Youth HIV + AIDS Awareness Day

All this activity occurs early in the life span of a galaxy, before it settles down into a quiet middle age.

WSJ: Book Review: Gravity's Engines

The remains investigated here span 3, 500 years of European prehistory, from the Early Neolithic to the Bronze Age.

BBC: Making of Europe unlocked by DNA