You ever wonder how they come up with these numbers? Do they sit at a table having coffee and say I think it should be "x" years and then they have a vote?
There are a number of dating methods used to date these finds -- each accurate to a greater or lesser degree. We'll have to read the paper to determine the methods used (they usually use more than one to eliminate any errors).
Instead of being sarcastic, you might do a little research on dating methods. That way, next time you spout off at least you might know something about which you speak.
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html