faint ring-shaped marring where oil filter gasket meets block

I just finished changing my oil at 10,000 miles and had it up on ramps this time so I could really see everything clearly. When I removed my old filter and wiped off the oil from where the previous filter's gasket contacted the aluminum block I noticed a faint circular ring pattern in the aluminum. I ran my fingernail over and across it and didn't really feel anything having any depth or courseness but nonetheless .. it must have been some kind of actual marring of the surface since it would not wipe off. At first I thought maybe it was rubber from the gasket still adhesing but it wasn't.

I did go back and bring up the adobe diagram that was posted on the forum called 'PRIUS MAINTENANCE - CHANGING OIL'. Upon inspecting the document particularly the picture imaging the area after the filter was removed, I believe this image illustrates a similar ring engraved on what is being referred to as the 'outer ring' - same thing I saw on my change ?

I'm thinking this may be typical or at least not unusual. Should I be concerned? What could have caused this ? My new filter is sealing/seating fine without leaks which is not surprising because like I said, my fingernail didn't seem to get caught on the surface as a ran it over the length of the 'scratch'. I have to assume it to be superficial. It is curious though.

Thanks in advance.

 

Thank you for your comments and sharing your observations !