They often leave marks like this on trees when sharpening ... by glaciers they moved around slightly and had rocks within them that created scratches on the surface. I've seen loads of examples ...

If you're dealing with scuff marks or very shallow scratches ... Regularly cleaning your pavers removes rocks and debris that ...

The age of the lines and how they were formed still needs to be verified, but there is a chance this may be one of the oldest symbolic stone carvings made by our human ancestors – at least 100,000 ...