IRA FLATOW: This is “Science Friday.” I’m Ira Flatow. Coming up later in the hour, we’ll be unpacking the myths of spoiled food. How long can mayonnaise stay out before it goes bad? What do those dates on meat packaging really mean? 

And we’ll be answering your questions, so give us a call, 844-724-8255. What would you like to talk about? You make the call, but you have to make the call, 844-724-8255. 

But first, if it feels like you’ve been hearing about an unusual number of tornadoes recently, you are not wrong. There have been reports of at least 1,000 tornadoes in the US this year, 200 just in the past two weeks. The unusually high number has to do with the current shape of the jet stream. 

And yes, there is a link to climate change. Here to tell us more about that story as well as other short subjects in science is Sarah Zhang, staff writer at The Atlantic. Sarah, welcome to “Science Friday.” 

SARAH ZHANG: Hi, great to be here. 

IRA FLATOW: So what’s this extreme tornado season? There was a tornado warning here in New Jersey— I mean New York— just this past week. What’s going on? 

SARAH ZHANG: Yeah, I live in Washington DC, and we also had a couple of tornado warnings this past week. So the reason that we’ve been having these tornadoes has to do with this unusual pattern of the jet stream across the United States. So the jet stream is this river of air. It’s really high up in the atmosphere. It’s far above our heads. And it usually blows west to east, and it circulates the globe. 

Sometimes its path can get a little bit curved. And in the past couple of weeks, it’s just been extremely curved. It’s basically formed a U across the United States. And inside this U, you have this blob of cold air. It’s kind of over California and the Northwest, in the Southwest. And that’s been unusually cold for the past couple of weeks. 

And outside of this U of the jet stream, you have warm air coming up from the Gulf of Mexico. And the rest of the country has actually been having a heat wave. And the basic recipe for a tornado is cold air meets hot air, and then you have the winds of this jet stream. And that’s basically what we are seeing in the middle of the country. We’re seeing all these hundreds of tornadoes all of a sudden. 

IRA FLATOW: So why is the jet stream acting so weirdly, out of place? 

SARAH ZHANG: Yeah, there are a couple of possible explanations. One is just the normal oscillations in the Earth’s weather. So there’s something called the Madden-Julian oscillation. And it’s kind of like El Niño, except it plays out in the span of a few weeks rather than years. And basically what it means is it’s created this batch of thunderstorms over the Indian Ocean. And this has actually had ripple effects that has affected the path of the jet stream over North America, so everything is connected. 

And the other, of course, is, what is the role of climate change? So it’s been also really warm in Alaska this year. And there’s this bubble of warm air that seemed to maybe have pushed the cold air that is in the U of the jet stream down. And as the Arctic gets warmer— it’s possible you might be seeing more of that obviously. 

It’s always really hard to say this particular event happened because of climate change. But as things happen in the future, we’ll see. We might see more of that cold air coming down. Then we can see how it’s going to affect tornadoes in the future. 

IRA FLATOW: Well, just the new normal. Next up, there was an amazing picture of a fossil I saw this week. It was like a whole school of fish fossilized at once. How does that happen? 

SARAH ZHANG: Yeah, it’s almost like a photograph, right? It’s 259 tiny little fish. They’re all swimming in the same direction. And you can see their little eyes and their little spines and little fins. 

And the scientist who saw this in the museum— he was actually interested in animal behavior. And he thought that, oh, maybe this was they all died at once. And maybe it’s a sand dune collapsed on them, and that explains why they look like this. 

I spoke to some other paleontologists. They were a little skeptical of the idea. They thought that maybe these fish did die all at once. Maybe it was like a volcanic eruption or a hit like a bubble of water with no oxygen. But then they sank down to the lake bed, and maybe there was a current that was moving along the fish and aligned them all at once. Whatever it is, they did die all at once. And—

IRA FLATOW: It’s just amazing. 

SARAH ZHANG: —that’s really unusual, yeah. 

IRA FLATOW: Yeah, a lot of maybes there. All right, you’ve been following a group of scientists who are testing the DNA of books. Books have DNA in them? 

SARAH ZHANG: Yeah, well, at least old books do. So if you remember before we had paper, we had parchment. And parchment is made of animal skin, usually cows or sheep or goats. And skin obviously has DNA in them. 

So I’ve been talking to a scientist name Matthew Collins. He’s actually a bioarchaeologist. And he got into this because he was originally digging up bones and trying to figure out how sheep were domesticated in Europe. The problem with bones is that if you’re lucky, you might find a couple dozen of them. 

And he was just in an archive one day and just had this epiphany. He was like, wow, I’m surrounded by so many books made of parchment. Like, literally hundreds of sheep and goats are on these shelves. 

IRA FLATOW: And so he decided to do DNA analysis of the paper or the parchment, as you say. 

SARAH ZHANG: Yeah, the parchment, exactly. So he could actually take— you don’t actually even need to cut up the parchment, which is important for people who are conservators of old books. You can actually just take an eraser like you might buy in the store and lightly rub it over the parchment. And this is actually something conservators do to clean manuscripts. You can just take those eraser crumbs, and you can get the DNA from animals from those crumbs. 

IRA FLATOW: That is cool. So you have different pages. You could tell which animal the different pages of the parchment came from. 

SARAH ZHANG: Yeah, exactly. You can go down to the level of individual animals. You could say, like, this page, this sheep on page 10— how is it related to the sheep on page 25? And you could ask, what kinds of breeds of animals were being used back in the Middle Ages? And what does that tell us about trade in Europe back in the time? 

IRA FLATOW: That is cool. Finally, some discouraging news for the scientists who thought they discovered an exomoon? 

SARAH ZHANG: Yeah or maybe not an exomoon. So last fall, if you remember— an exomoon is basically a moon that orbits around a planet in another solar system. And last fall, scientists thought they discovered the first one. 

But recently, there have been a couple of groups who have looked at some of the same telescope data. And they were like, we’re not sure if we see a moon. Maybe it’s an artifact in the data, or maybe it’s a planet, question mark, question mark. 

I think this kind of shows us how hard it is to find exomoons because they’re so distant and we can’t actually see them. Where we’re actually looking at is as they pass in front of a star, that star gets just a little bit dimmer. And that’s just really hard to analyze. But in those little tiny blips in the data, astronomers are trying to find planets and moons. 

IRA FLATOW: Yeah, well, we’re still looking for planet nine, so—

SARAH ZHANG: Yeah, exactly. 

IRA FLATOW: All right, Sarah Zhang, thank you for taking time to be with us today. 

SARAH ZHANG: Thank you. 

IRA FLATOW: Sarah Zhang, staff writer at The Atlantic.