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The Story of Thorium

The other day, benthic ecologist David Shull, from Western Washington University, came up to me, all excited. “We think we’re seeing the bloom hitting the bottom!” he said, and led me to a computer in another room to show me the evidence. There it was—a little red triangle that meant his seafloor mud sample had a lot of thorium 234.

“A lot of what?” I hear you cry. Why, I’m so glad you asked! Thorium is an element, like carbon, uranium, gold, or selenium. Like a lot of elements, it comes in several weights, and some of those weights are radioactive. Thorium 234 weighs 234 daltons (234 times the weight of a hydrogen atom.) It’s produced when uranium 238 decays, spitting out two neutrons and two protons.

Thorium 234 doesn’t do anything, biologically speaking. It doesn’t eat stuff. It doesn’t kill stuff. It’s radioactive, but it’s not dangerous in the quantities we see out here. But thorium does something interesting: when it’s in water, it tends to stick to particles. And that makes it very useful to people who are trying to understand what particles in the ocean do. The particles are tiny, but scientists can find them by looking for thorium.

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