Apollo 14 returned the Apollo program to flight following a nine-month stand down to investigate and fix the critical issues that led to the in-flight failures on Apollo 13. Apollo 14 marked the return to spaceflight of the first American in space, Alan Shepard. He and Mitchell spent over 33 hours on the Moon's surface, conducting moonwalks, collecting samples, and performing experiments. They landed at the site Apollo 13 was intended to have explored. From lunar orbit, Roosa photographed the planned landing site for Apollo 16. The mission returned the the oldest known Earth rock from the Moon, dating back 4 billion years. This was the first mission to use a single-color suit for one crewmember and a suit with red stripes for the other to allow visual ID of which astronaut was who during moonwalks. Use of the red stripe has been continued on every U.S. moon- and spacewalk since and has been adopted by Russia as well.