WASHINGTON :Scientists have recovered the oldest-known RNA, a molecule necessary for most biological functions, from a woolly mammoth that inhabited Siberia about 39,000 years ago, showing it can last longer than previously known and promising a new path for studying organisms that lived long ago. The RNA, successfully isolated and sequenced, was extracted from muscle tissue in the left front leg of a juvenile male mammoth, perhaps five to 10 years old, whose carcass was discovered in 2010 in