A throwing spear was found in Austria, and a 0.2 microgram sample (dry, .03mm x .03mm x .2mm) contained 2500 atoms of 14C. Knowing that 14C has a half-life of 5730 years, and presuming that such a sample would have originally contained 80,000 carbon-14 atoms (as growing trees did in the 1930's), how long ago did the spear-tree stop growing?