Thanks again to RAZD for the science lesson. I'm in awe of the power of something most people don't think of every day: radioactive decay. All that energy inside the earth, billions of years after it formed. It's like that article I found which mentions an angular unconformity in the mountains of Scotland. These mountains themselves have been severely eroded over many millions of years. Yet within them is evidence of dramatic uplift in the even more distant past -- mountains which formed, eroded to the point where they were flat, sank, and received horizontal sedimentary layers on top. Within existing mountains which themselves are old.

Rocks. Simple, common things. They can teach us so much.