[JimRed]

...how do we know someone hasn’t been messing around with them?

If that was the case the scratches would be fresh rather than weathered?

[smokingfrog]

Mmmm.

Not really all that convincing. The shell is supposed to be 500,000 years old, and there is naturally going to be some weathering, but how do we know that the scratches are maybe only 10,000 years old?

http://www.nature.com/nature/journal/vaop/ncurrent/fig_tab/nature13962_SF5.html