When fifth-graders at Green Acres Elementary in Lebanon, Oregon asked the NPR Skunk Bear team how pencil lead was made, they looked into it… way into it. From the start of the universe (with a shout out to Carl Sagan) to a pencil-making factory in Jersey City, New Jersey (est. 1889), this is A Sketchy History of Pencil Lead. Just one of the many fascinating details from the vid:

In 1779, scientists showed that pencil “lead” wasn’t lead at all. It was made entirely of carbon. A few years later, another pure-carbon mineral was revealed: diamond. The two substances couldn’t be more different. Graphite is dark and brittle. Diamond is clear and incredibly strong. How could they have the same chemical makeup?

In the 1920s, the answer was revealed. In diamond, carbon atoms are stacked in a pyramid, forming tight, strong bonds. In graphite, carbon is arranged in sheets. Within these sheets, atoms form a sturdy, hexagonal lattice. But the bonds between those sheets are weak — they slide apart with ease. When you drag graphite across paper, those sheets slough off.

The layer of graphite left on the paper is incredibly thin — a thousand times thinner than a human hair. That means, according to mathematician John Barrow, a single pencil could draw a line over 700 miles long.

Read more at NPR.org: Trace The Remarkable History Of The Humble Pencil.

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