<http://schema.org/dateModified>
"2013-08-13T18:22:55-04:00"^^<http://schema.org/Date>
<http://www.upi.com/Science_News/2013/08/13/Researchers-determine-age-of-oldest-known-North-American-petroglyphs/UPI-82191376432575/?spt=mps&or=5>