Graham Hancock shared the following 4 links, all dealing with engravings on a shell that are 500 000 year old.
http://www.iflscience.com/plants-and...ear-old-shells
http://www.nature.com/nature/journal...ture13962.html
http://www.news.com.au/technology/sc...-1227144411681
http://www.rappler.com/science-natur...y-homo-erectus