Puzzle 2 Answer

This is the footprint made by a waffle-sole athletic shoe.
In 1972, William Bowerman, one of the founders of Nike, Inc. and former track coach of University of Oregon, invented the waffle-like sole.  Before this, atheletes can only choose between heavy spiked and flat shoes.  Waffle-like soles are light-weight and provide traction.  These shoes became popular in the 1970s.

Source of information: 

Encarta Encyclopedia 

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