Lightning Can Produce Carbon-14

In a surprise announcement, Japanese researchers found that lightning bolts can be powerful enough to cause nuclear fission, leading to new isotopes— including carbon-14.

For decades, we have been told that carbon-14 is generated only by high-energy cosmic rays striking the atmosphere, hitting nitrogen atoms. Carbon-14 (14C) is one of the leading dating methods for organic remains up to a maximum of 100,000 years. Now, researches from the Kyoto University watched lightning bolts generate gamma rays and positrons, indicating that nuclear fission was occurring. One of the products, they believe, is 14C. Their paper in Nature says,

There are only two known natural origins of carbon isotopes on Earth: stable primordial ¹³C from geological time, which originated from stellar nucleosynthesis, and semi-stable ¹⁴C, which is produced via atmospheric interactions with cosmic rays. The lightning-triggered atmospheric nuclear reactions provide a previously unknown channel for generating isotopes of carbon, nitrogen and oxygen (¹³C, ¹⁴C, ¹³N, ¹⁵N and ¹⁵O) naturally on Earth. The short-lived isotopes ¹³N and ¹⁵O provide a new methodology for studying lightning, via positrons observed from the ground. The more stable ¹³C, ¹⁴C and ¹⁵N isotopes contribute to the natural isotope composition on Earth, albeit only a small fraction.

They don’t really know what that small fraction is, however. David Castelvecchi says in a companion article in Nature,

The main source of the carbon-14 in the atmosphere has generally been considered to be cosmic rays. In principle, lightning could also contribute to the supply. But it is not clear yet how much of the isotope is produced in this way, says Enoto, in part because it’s possible that not all bolts initiate photonuclear reactions.

Lightning storms from Earth orbit (NASA)

Jim Wild from Lancaster University explains the significance of 14C for dating in his article on The Conversation:

In nature, 14C is incredibly rare and makes up only about one in a trillion carbon atoms. But, apart from its weight and radioactive properties, 14C is basically identical to the more common carbon isotopes. It oxidises to form carbon dioxide and enters the food chain as plants absorb the radioactive CO₂.

The ratio of 12C to 14C in a given organism will start to change when that organism dies and ceases to ingest carbon. The 14C already in its system then starts to decay. It’s a slow process since 14C has a radioactive half-life of 5,730 years, but it is predictable, meaning that organic samples can be dated by measuring the ratio of 12C to 14C still remaining.

If you pardon his dip into pagan mythology, Wild explains the significance of this finding about lightning:

These results are important as they demonstrate a previously unknown source of isotopes in the Earth’s atmosphere. These include carbon-13, carbon-14 and nitrogen-15 but future studies may also reveal others, such as isotopes of hydrogen, helium and beryllium.

The findings also have implications for astronomers and planetary scientists. Other planets within our solar system have thunderstorms in their atmospheres that might contribute to the composition of their atmospheres. One of these planets is Jupiter, which is fittingly also the god of thunder in ancient Roman mythology.

New Scientist considers a health warning from the discovery:

Thunderbolts and lightning are more than just frightening – they also create radiation. For the first time, we have definitive proof that lightning sparks radiation and even clouds of antimatter, though it’s not clear how or if this will affect the health of people on the ground.

None of the articles consider whether the finding will cause changes to radiocarbon dating results. That seems unlikely, since calibration of the method depends on the ratio of carbon-14 to carbon-12 in the atmosphere, which was already known. However, it is significant that a discovery of this magnitude, involving something as common as lightning, was made this late in the history of physics.

Another belief about nuclear physics changed today. Using the IceCube detector at the South Pole, Penn State scientists determined that high-energy neutrinos can be stopped dead in their tracks by the Earth. Previously, it was thought that the slippery particles could pass right through Earth without even feeling it. Live Science says that the IceCube detector is located a mile down under the ice.

You, too, can still become a physicist and upset some trusted notions. In fact, Kyoto University has set up a crowdfunding program where the public could get involved, Science Daily says. Lead author Enoto made this comment about how the new discovery impacts us all: “We have this idea that antimatter is something that only exists in science fiction. Who knew that it could be passing right above our heads on a stormy day?”