Thanks to Brilliant for  supporting this SciShow video.

Brilliant is offering a 30  day free trial and 20% off an annual premium subscription for people  who sign up at Brilliant.org/SciShow. Living things need nitrogen, whether  you're a giraffe or a bacterium living two miles underground gathering your  energy from the radioactive decay of rocks.

Nitrogen is non-negotiable for the  chemical processes that make life work. Amino acids, RNA, DNA, and  chlorophyll all contain nitrogen. But even though most of  our atmosphere is nitrogen, it’s completely inaccessible  to most kinds of living things.

Which begs the question: what? For years, scientists have been  asking how nitrogen-dependent life could ever have gotten started in this  scenario of “water, water everywhere”. But now there may be an answer,  and it is, obviously, volcanoes. [♪ INTRO] Nearly 80% of Earth’s atmosphere is nitrogen  gas, which is two nitrogen molecules stuck together by not one, not  two, but three chemical bonds.

And this molecule is pretty inert, so most  organisms can’t do a single thing with it. That means nitrogen has to be fixed, or  chemically converted into a different form, before it becomes useful to an ecosystem. Humans can do this in factories, and we do a lot of it when we make synthetic fertilizers.

But in the non-manmade nitrogen  cycle, it happens in two ways. Lightning can fix a tiny bit of  atmospheric nitrogen by breaking apart the bonds between the two nitrogen atoms with immense amounts of energy  as it rips through the sky. And those free nitrogen atoms bond  with oxygen to make nitrogen oxides, which fall to the earth with rain.

But lightning fixes only  about 1% of all the nitrogen made available to organisms each year. The vast majority of nitrogen fixing  is done by single-celled organisms like bacteria and archaea,  which have evolved a way to drive a wedge between those stubborn triple bonds. Microorganisms in the soil and on the roots  of certain plants convert N2 in the air to ammonia, which is further converted by  different bacteria into nitrate and nitrite, which can be used by plants and other primary producers to be shuttled on up the food web.

This brings up an interesting  chicken and egg question: which came first, the bioavailable  nitrogen or the nitrogen-fixing microbes? Well – it’s not quite chicken and egg,  because it’s generally agreed that the nitrogen fixation that  seeded the first life on Earth must have occurred through non-biological means. It’s just incredibly unclear how.

So theories abound. The problem is that geological evidence  to support any of them… doesn't. For instance, some models suggest  N2 was belched into our planet's early atmosphere by volcanic eruptions,  and then lightning and frequent meteorite strikes converted it to nitric  oxide, which would have reacted with light and water to  produce nitrate and nitrite.

The problem here is, this would have taken ages. By some estimates, this method would  have resulted in nitrogen fixation happening anywhere between 50 to 5000  times slower than what we see today. It’s also been suggested that atmospheric  nitrogen could have been converted to ammonium if it reacted with iron,  magnetite or iron sulfide minerals under high temperatures in the  vicinity of hydrothermal vents.

But nobody's observed that actually happening. So there are other, less likely theories  about how the early Earth's nitrogen cycle got its start, but many researchers  think electrical discharges from lightning is kind of the  only thing it could have been. But if thunderstorm lightning  isn’t enough, then what?

One team of researchers has presented  evidence that lightning is what did it, thanks to volcanic eruptions. Volcanoes can make a lot of lightning,  caused by little bits of rock and ash bumping into each other and  electrifying inside the volcanic plume. One 2022 eruption produced 400,000  lightning strikes in just 6 hours.

In a 2024 paper in the journal PNAS,  the team suggested that massive volcanic eruptions on the early Earth  could have fixed a bunch of nitrogen. That means primordial volcanoes were the nurseries of the earliest version of Earth's nitrogen cycle. Kind of by accident, the research team  stumbled across the possible solution to the mystery surrounding the origin  of Earth's first fixed nitrogen boom.

They were poking around in the volcanic  deposits of two long-dead giant volcanoes in Turkey and Peru for a climate  study focused on sulfates. But they noticed that the deposits contained  shocking amounts of fixed nitrogen. They compared these deposits  to those of a much younger, though still huge, eruption in Italy to test  whether the arid climates or the extreme age of the other volcanoes had made a  difference to their nitrogen content.

But no, all the deposits were full of nitrogen. So where did it come from? To find out, the researchers tested  the isotopic composition of the oxygen, not the nitrogen, in the deposits.

They looked at how many neutrons  each oxygen atom contained.   Oxygen-containing molecules can  originate from almost anywhere, like water or sulfate belched  out of the bowels of the earth. But the specfic oxygen isotopes in the  nitrate and sulfate found in those volcanic deposits could only have come from ozone,  which is strictly an atmospheric gas. And that means that the nitrate had to be  formed by chemical reactions in the air.

Pretty surprising, considering  that the stuff that's belched out of a volcano  originates deep in the ground. So, the nitrogen must have  been fixed by lightning. Which must have been a lot of lightning.

Like a sight to behold! And the research team suggests that  a big eruption might fix 60 teragrams of nitrogen, which is like 60 billion  kilograms if I’m moving the decimals right, or about 132 billion pounds! Thunderstorm lightning could never fix  nitrogen on that scale or in one place.

A volcano, though, could provide a  huge shot in the arm to the surrounding environment, in addition to other  nice minerals that might have been really helpful to kickstart early life. You probably wouldn’t have wanted to be  anywhere near these volcanic eruptions. And even if you think you might, the  residents of Pompeii would like a word.

But that choking inferno of ash and lightning  may be responsible for you, bacteria, plants, and everything alive today. As if the power of volcanoes didn’t  command enough respect already. Thanks to Brilliant for  supporting this SciShow video!

Brilliant is an interactive online  learning platform with thousands of lessons in science, computer science, and math. They offer case studies,  puzzles, and tons of unique ways to help you engage with each topic. Brilliant recently launched a  ton of new content about data, all of which uses real-world data to train you to see trends and make better-informed decisions.

You can learn how to parse and  visualize massive datasets, making them easier to interpret. And I’m not talking about made up examples. With Brilliant, you’ll gain  insight by working with real data sets from sources like  Starbucks, X, Spotify, and more.

Once you feel comfortable working with  all of this data, you can check out Brilliant’s science, math, and computer  science courses to apply your knowledge. You can find them all at  Brilliant.org/SciShow or in the link in the description down below. That link also gives people who sign up 20% off an annual premium Brilliant subscription.

And you’ll get your first 30 days for free! Thanks for watching SciShow! [♪ OUTRO]