It's not the pen that's mightier than the sword — the lead in the humble pencil contains the strongest substance on Earth.

That finding, just published by Columbia University researchers in the journal Science, could lead to ultralight, paper-thin aircraft parts, super-tough bulletproof vests and even a 23,000-mile elevator to space long dreamed of by scientists.

Pencil lead — commonly known as graphite — is made up of one-atom-thick graphene sheets squeezed together. To learn about graphene's strength, postdoctoral researcher Changgu Lee had to figure out how to peel graphene sheets from graphite.

Once Lee found some defect-free graphene flakes — each 1/100th the width of a human hair — researchers tested their strength by trying to pierce them with atom-sized metal and diamond probes.

Professor Jeffrey Kysar, a mechanical engineer, explained graphene's strength this way: Lay a graphene sheet as thick as Saran Wrap over a muffin cup, and try to pierce it with a pencil.

"The force required to push that pencil through the graphene would be equal to the weight of an elephant or a small car," Kysar said.

"This is probably about 100 times stronger than the best steel you can buy."

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