In the run-up to the dropping of two devastating atomic bombs that led to Japan's surrender in World War II, American scientists raced to manufacture a bomb material that would yield enough destructive energy as part of the Manhattan Project. One of those efforts led to the synthesis of plutonium, which — although it occurs in trace amounts in nature — had never actually been seen by humans.

The first visible chunk of plutonium, which weighed only 2.7 micrograms, was created in the early 1940s by a team at UC Berkeley led by Glenn Seaborg, who would go on to win the Nobel Prize for chemistry in 1951. That chunk had been on display at Berkeley's Lawrence Hall of Science until 2007, when it was placed in storage during a renovation; it wasn't until recently that a physicist rediscovered the shard (encased in a plastic box) in a storage facility. Researchers recognized the historical significance of it and now plan to return it to public viewing, although they haven't yet decided what form that'll take.

Despite the element's dark origins rooted in the throes of World War II, Berkeley nuclear engineer Eric Norman assures that this particular chunk isn't dangerous. "The amount of radioactivity in this sample is incredibly low and is not a health hazard to anybody," he says.