Facebook Ads

I just had a rather unnerving experience with a Facebook ad, similar to what we were talking about earlier today during the final exam discussion. I was on Facebook just now and I noticed an image of the top of a mountain that looked strangely familiar with a caption that just said "Manisa". I clicked the photo and it brought me to a page talking about the city that contained "Niobe's Rock" on Mount Sipylus. I realized then what I had recognized about the image and the reason why it had appeared as an ad to me. I had recently made a project for Latin about the myth of Niobe where she is transformed into this very rock, and Facebook must have noticed some post I had made about the project. I am a little worried by this because in the past I had believed that Facebook only pulled information from things I had chosen to like or groups I had joined, not any post I may have made on a friend's wall or a status update. This experience really made me realize how much information Facebook actually pulls from your profile to make more directed ads.