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  • The Mariana Trench is the deepest, darkest part of our ocean.

  • At a maximum depth of 11,000 meters, it's an extreme place that's home to borderline

  • alien-looking creatures.

  • Scientists like to visit the trench to understand how life could possibly survive

  • and on one trip, a group found something unexpected inside the muscle tissues of deep sea crustaceans.

  • There were traces of bomb carbon, or carbon-14; a special radioactive isotope that surged

  • into the atmosphere after decades of nuclear weapon tests.

  • While it's a surprise that a human signature somehow found its way that far down -- there

  • are actually traces of bomb carbon everywhere, even inside you.

  • During the Cold War, we tested a lot of nuclear weapons.

  • When a bomb goes off, you had nuclear reactions of either fission or fusion occurring, with

  • a large amount of neutrons being basically blasted in all directions from the center

  • of that explosion.

  • Those extra neutrons in the atmosphere made extra carbon-14.

  • Carbon-14 is a naturally produced radioisotope.

  • It's made in the upper atmosphere from cosmic ray interactions with gas atoms.

  • But during that period of time when we set off hundreds of nuclear bombs...

  • the concentration of carbon-14 in the atmosphere almost doubled.

  • So, you see a very high spike.

  • When they stopped doing

  • tests, the concentration in the atmosphere started to go down.

  • The carbon-14 was still there.

  • It hung out in the atmosphere until it combined with oxygen to make carbon dioxide and then

  • that carbon dioxide started to get pulled out of the atmosphere, getting incorporated

  • into the biosphere and into the oceans.

  • So everything that's alive at that time was labeled with this extra carbon-14 and that

  • increase is called the bomb pulse.

  • Everyone who's alive now has some of the bomb pulse in them.

  • It may sound concerning, but the amount of bomb carbon you have in you isn't harmful.

  • There is natural radioactivity everywhere.

  • Everything that's alive is radioactive as well as have carbon-14.

  • In a surprise twist from the atomic testing era, Bruce and his colleagues uncovered a

  • way to use traces of that bomb carbon to clock the age of human cells and tissues.

  • I was at an American Chemical Society meeting where there was a special focus session on

  • the use of accelerators in nuclear chemistry.

  • Another speaker in that session was looking at metals in Alzheimer's plaques.

  • He said, "We don't really know how old the plaques are."

  • And I thought, hmm, I think I know a way where we could actually measure that.

  • And that was my start of doing bomb pulse biology

  • Every tissue turns over at different rates.

  • Different types of cells are being born and replaced, some turn over very, very quickly.

  • You may be a certain age, but your skeleton is likely a different one.

  • So how do you measure the amount of bomb carbon in something as small as a cell to find a

  • birth date?

  • Well, you need a couple things.

  • First, an understanding of how to do radiocarbon dating, a technique that's been around since

  • the 1940s.

  • Carbon comes in basically three different flavors.

  • 99% of carbon is carbon-12, it has six protons and six neutrons.

  • Carbon-13 has again six protons, but now seven neutrons.

  • Carbon-14 has six protons and eight neutrons.

  • All that chemistry is the same, but we can actually trace the different atoms by mass.

  • Because carbon-14 is radioactive with a half-life of about 5,730 years, the concentration of

  • carbon-14 actually decreases over time.

  • And that decrease in carbon-14 concentration is what's used to do radiocarbon dating.

  • By measuring the ratio of carbon-14 in a sample to the amount of carbon-14 in the atmosphere,

  • they can decipher the age.

  • But figuring out how much there is in tissue requires skills in advanced chemistry and

  • a really big machine.

  • The measurement is actually fairly easy.

  • The chemistry that goes into doing a sample prep is really the hardest thing to do.

  • We need about 10 million cells to get enough DNA to do an analysis.

  • Once you've separated the different type of cell that you want, then you have to harvest

  • the DNA and clean it up We add some copper oxide to it and evacuate

  • a tube and seal it with a torch.

  • We then combust that material to convert all that carbon to carbon dioxide again.

  • That carbon dioxide gets reduced to elemental carbon in ion powder and that's actually

  • what we measure in the ion source.

  • Once they've got that down, they'll put the samples into targets for the mass spec

  • accelerator.

  • The targets are little aluminum sample holders that have a little hole in them about a millimeter

  • in diameter.

  • It then goes into a sample wheel and put in the ion source.

  • We use a cesium sputter ion source and it makes negative ion we set up an electric field

  • to extract the negative ions out of that through the plasma mass that's right in front of the

  • target.

  • We have this negative ion beam that's coming out of the ion source.

  • We then put it through a low energy magnet to select the mass that we want.

  • It gets injected into the accelerator.

  • The accelerator has a very high positive voltage at the center, it's called the terminal.

  • We then have a couple of focusing elements, a couple more magnets, and then we measure

  • carbon 14 counts in a particle detector at the end.

  • This precise atom counting technique has uncovered some incredible things about our bodies.

  • Ever wonder why an Achilles tendon injury takes so long to heal?

  • It's because the tissue turnover is practically nonexistent.

  • This finding is just one of many other discoveries thanks to bomb pulse forensics.

  • Cardiomyocytes are the muscle cells of the heart.

  • We saw that there was turnover, relatively low like 1% turnover, but it did occur.

  • Why that's important is that you might be able to clinically stimulate an injured heart

  • to repair itself.

  • This was huge because previously, we didn't know adult heart cells could replenish.

  • We found that the only place there seem to be any turnover of neurons was in the hippocampus.

  • Hippocampus is where our short term memories become long term memories.

  • And in another study using the bomb pulse, they uncovered that fat cells are forever.

  • People get new fat cells through adolescence, and then the body seems to maintain that number.

  • So when you swing through weight gain and weight loss the number of fat cells is staying

  • the same.

  • But, with all this investigative potential, there's a catch.

  • The bomb pulse is essentially going away.

  • But there's another factor that's actually pushing the C-14 lower because we've been

  • burning fossil fuels and fossil fuels are very, very old carbon... it's actually pushing

  • the C-14 concentration down.

  • The atmosphere will return to pre-bomb levels by roughly 2025.

  • Until that happens, Bruce and his team are racing against time to uncover as many new

  • medical findings as they can.

  • Because, no one wants to explode another bomb for the sake of scientific research.

The Mariana Trench is the deepest, darkest part of our ocean.

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