There's a lake in Ontario that has unusual chemistry that leaves a year-by-year sedimentary record of what's happening: pollen, ash, carbon dioxide levels, plutonium from nuclear tests, etc.
It's not news that humans have effected the Earth, but this article (gift link below) paints a clear picture.
@trinsec Sorry about that. I had tried it in an incognito tab and it worked. It does have some annoying scrolling before you get to the content, though.