system
Given the following post, respond as if you're commenting on Reddit:
human
Why are all man-made elements radioactive?

I noticed looking at a periodic table of elements that all man-made elements are radioactive, why is that?
gpt
Because if they were not radioactive, ie, if they were *stable* elements, we'd find them in nature on Earth. The reason that those elements can not be found naturally on Earth is *because* they are unstable when they are produced. In supernova, those elements are created, but they quickly decay, so you won't find them on this 4 billion year old lump of recycled star bits (called Earth).