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We Found Radioactive Traces From Nuclear Bombs in the Mariana Trench

Nuclear Bombs in the Mariana Trench

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.
We Found Radioactive Traces From Nuclear Bombs in the Mariana Trench
We Found Radioactive Traces From Nuclear Bombs in the Mariana Trench
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 number 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 time when we set off hundreds of nuclear bombs... the concentration of carbon-14 in the atmosphere almost doubled. 
We Found Radioactive Traces From Nuclear Bombs in the Mariana Trench
We Found Radioactive Traces From Nuclear Bombs in the Mariana Trench
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 alive at that time was labeled with this extra carbon-14 and that increase is called the bomb pulse. Everyone alive now has some of the bomb pulses 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 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 types of cells 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 puts it 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 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 seems 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.

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