Podcast: Mysteries of the ancient mantle, and the Hitchhikers Guide to the Galaxy

Host: Noah Baker

Welcome back to the Nature Podcast. This week: explosive eruptions from the deep Earth.

Host: Benjamin Thompson

And revisiting a science-fiction classic, 40 years on. I’m Benjamin Thompson.

Host: Noah Baker

And I’m Noah Baker.

[Jingle]

Host: Benjamin Thompson

First up on this week’s show, we’ll be learning about the ground underneath our feet, a long way underneath our feet. The Earth’s mantle is sandwiched between the planet’s outer core and the thin crust we walk about on. Although the mantle makes up a huge 84% of the Earth’s volume, this enigmatic zone is difficult to study. But thanks to an unusual type of explosive eruption bringing deep rock samples to the surface, we can get important clues as to its composition. Jon Woodhead from the University of Melbourne in Australia has been studying new and old samples of these rocks known as kimberlites. Geoff Marsh got him on the phone to uncover their secrets.

Interviewee: Jon Woodhead

So, kimberlites are very rare volcanic rocks but they’re not really like most other volcanic rocks. In fact, they actually come from the deepest depths of any samples that we have.

Interviewer: Geoff Marsh

And they get to the Earth’s crust quite violently, don’t they? Paint a picture for us of a kimberlite eruption.

Interviewee: Jon Woodhead

So, when most people think of volcanic eruptions they think of typical volcanic cones, such as Mount Etna or Stromboli – relatively gentle volcanic eruptions. Kimberlites are quite different. They’re extremely energetic, volatile, rich eruptions and they just blast holes through the crust. They don’t form any sort of organic edifice. They just leave a huge crater in the ground.

Interviewer: Geoff Marsh

Given that we’ve never been able to directly observe the mantle, how do you know how deep these kimberlite rocks actually come from?

Interviewee: Jon Woodhead

It’s really because they bring up diamonds and the diamonds have trapped within them high-pressure minerals that we know must have formed at great temperatures and pressures, great depths of the Earth.

Interviewer: Geoff MarshSo, tell me about your kimberlite dataset then and exactly what you did to unravel their secrets.

Interviewee: Jon Woodhead

So, we very carefully gathered together kimberlites from around the globe. There are samples that cover the past 2.5 billion years of Earth history. We dissolved them. We extracted different elements from them. In particular, two elements – neodymium and hafnium – and we measured their isotopic composition and to our great surprise, they appear to all derive from a single deep mantle source. Their isotopic compositions remain constant through time, essentially.

Interviewer: Geoff MarshAnd you suggest in your paper that their isotopic composition reflects a sort of primitive chemistry of the Earth’s mantle. How do you come to that conclusion?

Interviewee: Jon Woodhead

Well, their composition is very similar to a class of meteorites called the chondritic meteorites and they have a composition that we think best reflects that of the early Earth, just after the core formed. So, the fact that these kimberlites have that composition and it’s remained constant through time leads us to believe that there are still remnants of that very primitive early Earth still surviving in the deep mantle.

Interviewer: Geoff MarshPresumably that’s quite surprising, given how much we know things move around over time at the crust, that part of the mantle might have remained the same over more than half of the Earth’s history.

Interviewee: Jon Woodhead

Yeah, that’s right. Yeah, it’s actually quite surprising because we know that tectonic plates are continually being recycled back into the Earth’s mantle at subjection zones, and so there’s inevitably quite a mixture of components down there. But it still seems that some parts of the deeper mantle have remained preserved, and this is important to know from the perspective of understanding the planet’s geochemical evolution.

Interviewer: Geoff MarshSo, where exactly do you think this pristine reservoir is in the mantle because the mantle is pretty big, isn’t it?

Interviewee: Jon Woodhead

Well, we know that it can’t be in the upper mantle because we do have other rock types that source the upper mantle and they don’t show these compositions. It really has to be somewhere in the deeper mantle, and we know that kimberlites, at least some kimberlites, come from at least 800 kilometres’ depth and so that gives us our best estimate of where these materials may lie, at least at that depth.

Interviewer: Geoff MarshNow, you mentioned in your paper that some of the more recent kimberlites are slightly different in their composition. Does that muddy the story somewhat?

Interviewee: Jon Woodhead

Yeah, there is some evidence that the very youngest kimberlites – those just a few hundred million years old – have been perturbed slightly. But while there are kimberlites that show that feature, there are still some young kimberlites that show this primordial signature, so we believe that the bulk of the source is still intact, but that small regions of the source may have been perturbed relatively recently.

Interviewer: Geoff MarshSo, what’s next then for you?

Interviewee: Jon Woodhead

I guess, so far, we’ve only really found kimberlites that go back 2.5 billion years. It will be interesting now to try and find some older materials to try and extend this story a little bit, but kimberlites are quite rare rocks, so I’m not sure what our chances are of finding any older materials really. We rely on the diamond industry to find those rocks for us, I guess.

Interviewer: Geoff MarshI suppose a modern-day kimberlite explosion would be pretty interesting.

Interviewee: Jon Woodhead

Yeah, that will be great to see that, but from a distance, I guess.

Host: Benjamin Thompson

That was Jon Woodhead from the University of Melbourne talking to Geoff Marsh. You can read Jon’s paper and a News and Views article over at nature.com.

Host: Noah Baker

In this week’s News Chat, we’ll be hearing all about the opening of the world’s largest single-dish radio telescope – listen up for that at the end of the show. Up next though, Anna Nagle is here with this week’s Research Highlights.

[Jingle]

Anna Nagle

How is a champagne bottle like a fighter jet? No, this isn’t a joke, as it turns out that when a champagne bottle pops its cork, it unleashes a supersonic jet of freezing gas. Researchers in France trained high-speed cameras on champagne bottles to closely record what happens during that iconic moment when the cork shoots from the bottle. Watching the cloudy jet that forms as the pressurised CO2 in the bottle is released, the team spotted characteristic shockwaves that indicated the gas was travelling faster than the speed of sound. You can also see these so-called Mach disks in the exhaust trails of fighter jets. Celebrate that research over at Science Advances.

[Jingle]

Anna Nagle

Vaccination is an important public health tool to protect against disease. But new research from Canada suggests that in mice, the time of day you give a vaccination could affect how well it works. Circadian rhythms affect many physiological processes and cells, including immune cells, have their own internal clocks which change gene activity across a day. Researchers gave mice vaccinations at different times of day and looked at how particular immune cells responded. They found that shots given at midday stimulated the immune cells more than at any other time of day. Get a shot of that science over at Proceedings of the National Academy of Sciences.

[Jingle]

Host: Noah Baker

Next up, we’re setting off across the galaxy to discover hyperspace bypasses, fish shortages and existentially unhappy elevators, with only a small guidebook to lead the way. If you don’t know what I’m talking about, don’t panic. The answer is simple. This October marks 40 years since the publication of the classic book, The Hitchhiker’s Guide to the Galaxy by British writer Douglas Adams. Resident sci-fi geek Shamini Bundell is here to celebrate the anniversary and find out how far real science has come since 1979.

Interviewer: Shamini Bundell

The Hitchhiker’s Guide to the Galaxy is a book about a book. Both books are called The Hitchhiker’s Guide to the Galaxy, but while one is, as you might expect, a guide to the galaxy for hitchhikers, the other tells the story of Earthbound Arthur Dent and what happens to him when his home is demolished. The home in question is planet Earth, and author Douglas Adams describes the destruction of the Earth to make way for a hyperspace bypass like this:

There was a terrible ghastly silence. There was a terrible ghastly noise. There was a terrible, ghastly silence.

Interviewer: Shamini Bundell

Although the real Earth has managed to survive the last 40 years undemolished, some aspects of Douglas Adams’ imagined universe seem rather prescient. To discuss the real science within the famous science-fiction world, I’ve bought in what the book might describe as two hoopy froods with brains the size of planets. I’ve got Karl Ziemelis, Chief Physical Sciences Editor here at Nature, who’s seen many a paper on space, robots and other sci-fi staples cross his desk in his 27 years here.

Interviewee: Karl ZiemelisHi Shamini.

Interviewer: Shamini Bundell

And I’ve got Ed Gerstner, who’s chair of the Springer Nature Sustainable Development Goals Programme, so I’m guessing that means you’re doing your big to help make sure the Earth doesn’t get destroyed by a hyperspace bypass or otherwise.

Interviewee: Ed GerstnerIdeally, or climate change, but certainly how we can make the world a better place.

Interviewer: Shamini Bundell

So, the eponymous book of The Hitchhiker's Guide to the Galaxy itself, in the story, is supposed to be a huge repository of knowledge that an interstellar hitchhiker might need to make their way around the galaxy. This was how Douglas Adams described it:

The reason why it was published in the form of a micro sub-meson electronic component is that if it were printed in normal book form, an interstellar hitch hiker would require several inconveniently large buildings to carry it around in.

Interviewer: Shamini Bundell

And when Douglas Adams was writing that, that was true, like data needed actual buildings to store large amounts of it, right?

Interviewee: Ed GerstnerAbsolutely, but I think what’s interesting about this quote is the presumption that all the information will always be contained locally. Ten years ago, they were talking about terabytes of memory on just a very small, like a penny, could be stored, terabytes of memory, and we’re going that’s what I want so I can put all my music and all everything, and no one even tries to do that anymore because it’s all in the cloud, and Douglas Adams hadn’t even conceived that you’d have information in the cloud.

Interviewer: Shamini Bundell

Well, there were some things that were pretty hard to predict in 1979, but also some issues that were around then that just haven’t gone away. We’ve already mentioned the destruction of the Earth being a major plot point, but here’s a quote from the second book about a less dramatic way in which we’re destroying the Earth:

The trouble with most forms of transport, he thought, is basically one of them not being worth all the bother. On Earth — when there had been an Earth, before it was demolished to make way for a new hyperspace bypass — the problem had been with cars. The disadvantages involved in pulling lots of black sticky slime from out of the ground where it had been safely hidden out of harm's way, turning it into tar to cover the land with, smoke to fill the air with and pouring the rest into the sea, all seemed to outweigh the advantages of being able to get more quickly from one place to another — particularly when the place you arrived at had probably become, as a result of this, very similar to the place you had left, i.e. covered with tar, full of smoke and short of fish.

Interviewer: Shamini Bundell

Now, this is a much more realistic depiction of the problems facing us today than the Earth being destroyed by a Vogon constructor fleet and since this was originally published, scientific papers about how we’re destroying the planet in various ways have, presumably, become a lot more common.

Interviewee: Karl ZiemelisAbsolutely, the research endeavour has over the years sort of dug much deeper and deeper into just trying to understand more concisely, more clearly how the environment is changing around us and understanding the mechanisms and the processes leading up to that.

Interviewer: Shamini Bundell

And the doomsday scenario of The Hitchhiker’s is aliens are going to destroy the Earth.

Interviewee: Karl ZiemelisWell, I would just say bring it on! I’m just really excited at the prospect of publishing the papers that is the most convincing evidence of aliens. That’s going to be one hell of a coup if we get that paper.

Interviewer: Shamini Bundell

Just a shame there will be no one left to read it. But let’s discuss one more quote. So, in the books, the guide itself has entries on pretty much everything, and this is how the first book describes the entry on space:

Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space.

Interviewer: Shamini Bundell

Now, there’s not a lot of complex physics actually delved into in the books, but it sort of alludes to the fact that the Universe is complicated and we are a very small part of it, and is that something that with each new sort of physics of discovery, is reinforced?

Interviewee: Karl ZiemelisI mean astronomy has been going great guns for decades now and with each new revolution in instrumentation, we’re constantly being amazed. I mean at the moment, we’ve got a whole host of sort of like transient events, things that go bang in the night, which in the past, you had to be really lucky, looking in the right direction at exactly the right time at exactly the right wavelength to have seen this fleeting object or fleeting event, but now we’ve got the technology to really scour space and see a whole host of phenomena, events, big things happening, that we had no idea were going on.

Interviewee: Ed GerstnerI would just add to that the fact that the things that I learnt about at university were things our lecturer said, but of course, we’ll never actually detect a gravitational wave in our lifetimes, of course we’re unlikely to ever see a black hole in our life time, and yet all of these things have happened. I think that’s just as mindboggling as the fact that there are all these things that we don’t yet know about, the fact that we got so much of it right.

Interviewer: Shamini Bundell

There’s one final quote that I think applies to all of us here, possibly all of us here at Nature and in the scientific community which is from the original Hitchhiker’s Guide to the Galaxy book. Arthur Dent, the hero, talking to Slartibartfast, who says:

“What does it matter? Science has achieved some wonderful things of course, but I'd far rather be happy than right any day."

"And are you?"

"No. That's where it all falls down, of course."

"Pity", said Arthur. "It sounded like rather a good lifestyle otherwise.”

Host: Noah Baker

That was Michael Stacey there, reading quotes from The Hitchhiker’s Guide to the Galaxy series, with Karl Ziemelis, Ed Gerschner and Shamini Bundell, providing some irreverent commentary.

Interviewer: Benjamin Thompson

Finally on the show, it’s time for the News Chat, and I’m joined in the studio by Lizzie Gibney, senior reporter here at Nature. Lizzie, hi!

Interviewee: Lizzie Gibney

Hello, Ben.

Interviewer: Benjamin ThompsonWell, for our first story today then, we have a story that you’ve written about a massive telescope.

Interviewee: Lizzie Gibney

That’s right. This is a radio telescope in China and they’ve been building it for about five years now and it is finally ready to hit the mainstream and officially end its commissioning period and start running for real.

Interviewer: Benjamin ThompsonThis is a big telescope but how big is big?

Interviewee: Lizzie Gibney

Pretty big. It’s 500m – half a kilometre – across, and it’s really impressive to look at actually. It’s just an absolutely enormous silvery coloured dish within this depression in a very, very remote location in China. It looks a little bit like a kind of Bond villain’s lair or something.

Interviewer: Benjamin ThompsonAnd what’s it designed for then, this sort of giant, half-a-kilometre wide dish?

Interviewee: Lizzie Gibney

So, it’s a radio telescope and it is the biggest one in the world, so it collects these very, very faint, kind of whispery radio waves that are coming in from the cosmos and it means that we’re able to study, in really exquisite sensitivity, really great detail, loads of different phenomena across the Universe.

Interviewer: Benjamin ThompsonWhat sort of things then in particular?

Interviewee: Lizzie Gibney

Well, there’s a huge variety. So, the kind of bread of butter of any radio telescope, so it’s able to look at the hydrogen emissions from distant galaxies and chart the Universe in that way. It’s also able to see pulsars, so these are the dead cores of neutron stars that are spinning and putting out this radio emission very, very regularly. But it’s also going to be able to do a few more kind of more intriguing things that have just become options in the last few years. So, for instance, it’s hoping to maybe be able to see exoplanets, so planets that are outside of our solar system and through their radio emissions, and that’s particularly interesting because radio emissions only come from exoplanets when they have magnetic fields and now on Earth a magnetic field has been really, really crucial to life and to having an atmosphere, so scientists are quite excited about this idea that we might be able to see planets and their magnetic fields.

Interviewer: Benjamin ThompsonSo, potentially a lot of applications then. Is it just simply it’s sheer scale that makes it better than other telescopes that already exist?

Interviewee: Lizzie Gibney

Pretty much. The more collecting area, the more kind of reflective surface you have, literally the more sensitive your telescope is, so in that way it’s better. It can see more faint signals than any other radio telescope that we have out there. But of course, you get cons along with the pros, so it’s not able to see a huge amount of the sky. So, if you’re looking for things which happen very randomly or very, very quickly like detecting new fast radio bursts, which are kind of mysterious fleeting blasts that we see happen out there, then it’s not going to be very good at finding new ones. But once we know that there is one there that repeats, you can then hone in and you can turn the huge power of this telescope on to studying that particular source, and that’s when it becomes really, really good.

Interviewer: Benjamin ThompsonHow do we go about turning this telescope to look at something? It seems very difficult to sort of manually push it to face a particular direction. How does it work?

Interviewee: Lizzie Gibney

So, when you want to focus on a different part of the sky, the way it actually works is it forms out of this one enormous dish, kind of different parabola within that by shaping these 4,000, I believe, different aluminium panels. So, it’s incredibly complex, and that’s one of the reasons that it was actually a really radical design and people weren’t entirely sure that it would work. So, in order to do this kind focusing on different parts of the sky, 2,000-odd different winches pull and push these little plates into the right place. So, it’s really quite a feat of engineering.

Interviewer: Benjamin ThompsonFinally on this story then, what’s the timeline? When will this telescope start collecting data for real?

Interviewee: Lizzie Gibney

Well, it has been collecting data for the past couple of years while it’s been going through this testing process, and that’s been quite exciting because actually it’s found like more than 100 pulsars already and all of these fast radio bursts, so we know that it’s working. But now it’s officially passed a series of tests that mean we know it’s working exactly as it’s supposed to and, in fact, exceeding that. So, there’s just going to be a review meeting now that happens very excitingly next month, which will be the green light basically from the Chinese government and that means it is now officially open for business and the upshot of that as well is that that means that international researchers will be able to bid for time on the telescope because up until now, it’s just been for Chinese scientists.

Interviewer: Benjamin ThompsonLet’s move on to our second story today Lizzie and it revolves around something that’s very dear to my heart and that is food, and particularly bananas, one of my favourite breakfast snacks. But bananas are in trouble.

Interviewee: Lizzie GibneyThat’s right. So, last month, the Colombian government confirmed that a fungus that kills bananas called TR4 has now invaded the Americas and that’s a huge problem because although this fungus has been around the world, the Americas is the source of most of the world’s banana supply. And then the really big problem is that a particular kind of banana called the Cavendish, which is by far the most popular in the world – it counts for about 99% of the global banana shipments – is susceptible to this fungus. So, potentially, we’re facing a huge problem.

Interviewer: Benjamin Thompson

Well, why not just sort of treat this fungus with fungicides or chemicals and what have you?

Interviewee: Lizzie GibneyUnfortunately, it’s a really, really tough fungus. It can’t be killed with fungicides and it actually lingers in soil for up to 30 years, which means that the normal ways that you might go about trying to get around it are not going to work.

Interviewer: Benjamin Thompson

So, we’ve got this unkillable fungus then and we’ve got a giant monocrop of bananas worldwide – it seems like a recipe for disaster. I mean why not just breed a more resistant banana?

Interviewee: Lizzie Gibney

Well, that would be a great idea except that unfortunately, that’s not possible with the Cavendish banana and that’s because it’s actually sterile, and so the way that you get new ones is just to clone it, so conventional breeding isn’t going to work here. One method that might work though is to genetically modify, to genetically engineer. So, there’s one group in Australia who is working on taking a gene from a wild type of banana and that is resistant to this particular fungus, and then putting that into the Cavendish banana, which is not resistant. They’ve done a couple of small-scale studies already and they’re now planting on a big half-hectare of land to see if they can have the Cavendish bananas grow despite this TRF infestation. So far, that trial is going well, but it probably won’t be until the study ends in 2021 that we know whether it’s really worked.

Interviewer: Benjamin Thompson

Well, a while to wait then. Is anything else in the offing?

Interviewee: Lizzie Gibney

So, another method that researchers are trying to use is the ever fashionable CRISPR. So, instead of inserting a gene from a different type of banana into the Cavendish, what they’re trying to do is actually just tweak the genome of the Cavendish in order to boost its resilience. So, there are a number of different ways that they’re trying to do that, trying to either turn on a dormant gene that actually would give resistance to TR4 or another group are trying to supress the genes that actually make it vulnerable. So, there are a couple of different strategies there. One issue though is how regulators are going to deal with these bananas.

Interviewer: Benjamin Thompson

This may be a daft question, but is there not just a different sort of banana that we could eat?

Interviewee: Lizzie Gibney

There might be. The thing is, the Cavendish is very popular for a reason. It has a particular taste, texture, it ships really, really well, so people are very keen to keep using the Cavendish, but of course, there are actually thousands of other types so it might be that we can either find another variety that is suitable or maybe people will have to change their tastes slightly.

Interviewer: Benjamin Thompson

Indeed. Well, thank you for joining me, Lizzie. Listeners, head over to nature.com/news for more on these stories and the latest updates from the world of science.

Host: Noah Baker

And that’s it for this show. But before you go, if you’re interested, head over to our YouTube channel where you can find a roundup of last Friday’s global climate strikes. Why did scientists take to the streets? That’s at youtube.com/naturevideochannel.

Host: Benjamin Thompson

And if you’d like to get in contact with us, you can do so on Twitter – we’re @NaturePodcast – or on email – we’re podcast@nature.com. I’m Benjamin Thompson.

Host: Noah Baker

And I’m Noah Baker. See you next time.