Has the world’s oldest known animal been discovered?

Host: Noah Baker

Welcome back to the Nature Podcast. This week, possible fossil evidence of the oldest animal ever…

Host: Benjamin Thompson

And eavesdropping on a glacier’s seismic whisper. I’m Benjamin Thompson.

Host: Noah Baker

And I’m Noah Baker.

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Host: Noah Baker

First up on the show, you might remember that last week we had a story about sponges. Well, it seems we’re not done. We have another sponge story coming up now, albeit from much further in the past. Here’s reporter Nick Petrić Howe with more.

Interviewer: Nick Petrić Howe

When did the first animals evolve? It’s a more difficult question than you might think.

Interviewee: Rachel Wood

Well, to be honest, we don’t understand when animals arose at all.

Interviewer: Nick Petrić Howe

This is Rachel Wood, a geologist with an interest in the evolution of life.

Interviewee: Rachel Wood

And this is for two reasons. First of all, the fossil record of animals is incredibly difficult to decipher. We have fossils which we, being palaeontologists and geologists, can put our hands on our hearts and say, ‘This is definitely a fossil animal.’ And certainly, many, many fossils in the Cambrian are undoubtedly animals. So, the Cambrian started at approximately 540 million years ago, so anything younger than that we can be pretty secure is an animal. But going back into older rocks, it gets more and more uncertain.

Interviewer: Nick Petrić Howe

Scientists are pretty confident that some fossils from around 550 million years ago are animals. But much earlier than that and things get much more murky. And hang on, didn’t Rachel say there were two major problems?

Interviewee: Rachel Wood

The other set of the problems – as if that wasn’t enough – is that the other way we have of trying to work out the origin of major changes in the evolution of life is to use what’s called molecular phylogeny. So, this is really just a family tree based on relatedness of DNA, and when you do this for elucidating the origin of animals, most molecular phylogenies suggest that the origin of animals was anywhere between approximately 650 and 850 million years.

Interviewer: Nick Petrić Howe

There are also many theories for what the earliest animals may have looked like. One points to sponges.

Interviewee: Rachel Wood

One of the reasons that sponges, in particular, are such a focus of interest is that they’re often accepted to be the most basal of animals.

Interviewer: Nick Petrić Howe

Sponges – and, yes, they are animals, think about that next time you’re in the shower – don’t have complicated nervous, circulatory or digestive systems. They survive by filter feeding from water. They also have far fewer cell types than other animals, so they may not be a bad place for an evolutionary start. And this week in Nature, there’s a paper that claims to have found a sponge from 890 million years ago. Here’s Elizabeth Turner, the paper author.

Interviewee: Elizabeth Turner

It consists of little tubules, okay, so they are 31 thousandths of a millimetre across, approximately, and they’re filled with little calcic crystals that are clear and translucent, and these little tubules are embedded in a groundmass of much more finely crystalline calcic crystals, so they look darker. So, what you see is these little wormy tubes inside a darker groundmass, and what’s important about the little tubes is that they anastomose in a very distinctive way. So, they form a three-dimensional meshwork of divergent branching and re-joining three-dimensionally, which is quite a complex microstructure that can’t be explained as being any of the other possible things that could have been around at the time like fungi or algae or bacteria.

Interviewer: Nick Petrić Howe

These little wormy tubes branch or anastomose in such a way that Elizabeth believes it points towards an animal origin – a sponge. Elizabeth believes that these fossils look very similar to some more recent fossils also thought to be sponges.

Interviewee: Robert Riding

I mean, I’ve got a picture on my screen now and I’ve got the two fossils side by side – the ones that we described 500 million years ago and the one that Elizabeth has found – and I honestly don’t see a difference in them. They look to be identical to me.

Interviewer: Nick Petrić Howe

This is Robert Riding, another ancient sponge-hunter describing a fossil sponge he recently published a paper about.

Interviewee: Robert Riding

We were looking at rocks that are much younger, about 500 million years old, and they’d always been thought to be stromatolites, which are calcified microbial mats like you see at present day in places like Shark Bay in Australia. But when you look at them closely, you see this delicate network of tubes which we are convinced are sponge fabrics, and they are interlayered with the stromatolite fabrics or the bacterial fabric. And the sponge fabrics in those are very similar. I would say they’re identical to those that Elizabeth has found.

Interviewer: Nick Petrić Howe

Robert and Elizabeth suggest that their fossils represent sponges that would have had a close relationship with bacteria. In fact, in the harsh 890-million-year-old world, they think a relationship like this would have been necessary.

Interviewee: Elizabeth Turner

So, they lives in a reef, okay. So, these reefs were built by photosynthesising organisms. And this is important because, at the time, 890 million years or so ago, Earth didn’t have a whole lot of oxygen in its atmosphere or its ocean, and animals obligatorily require a certain amount of dissolved oxygen in the water or in the atmosphere. And in fact, where I find them living is in the little pockets and crevices, little tiny caves just underneath the reef surface, little caves that are centimetres in diameter.

Interviewer: Nick Petrić Howe

Also, if these fossils are indeed sponges that lives 890 million years ago, that would mean that they survived some of the harshest parts of Earth’s history – a very cold period known as the Cryogenian, where it is possible that nearly all of Earth’s surface was frozen, referred to by some as ‘Snowball Earth’.

Interviewee: Robert Riding

So, that gives you, in a way, a handle on the glaciations. It means that there must have been life, even if we haven’t found it yet. There must have been animal life surviving the Snowball Earth glaciations.

Interviewer: Nick Petrić Howe

But as you might remember from the beginning, the further back in time you go, the more uncertainty. This fossil would predate any uncontentious animal fossils by several hundred million years. So, how likely is this to really be an animal fossil? Here’s Rachel again.

Interviewee: Rachel Wood

So, first of all, I’d like to say it’s great that this idea has been proposed. It’s going to cause a huge amount of discussion and debate, no doubt heated discussion and debate and controversy. The author is proposing that this is a sponge fossil based on its similarity to very, very similar fossils that are found in much younger rocks, but the problem is are these younger fossils themselves sponges? When you read the literature on this, it is actually slightly tentative. The proposal is that they are interpreted as sponges.

Interviewer: Nick Petrić Howe

Rachel, who wasn’t associated with this latest research, believes that there are other possible interpretations for this fossil.

Interviewee: Rachel Wood

I think a bacterial origin or some sort of general microbial origin, an origin of structures formed by biofilms, which are these sort of consortia or communities of different microbes that form slimy surfaces, they can create these interesting and seemingly complex microstructures. So, I think all this suite of microbial precipitate needs to be explored.

Interviewer: Nick Petrić Howe

On the other hand, the paper author Elizabeth is quite certain about her sponge interpretation.

Interviewee: Elizabeth Turner

Me, I’m quite confident, and that’s because I’m a carbonate petrographer. One of the things I understand really well in this world is limestones and how to understand the evidence of life that’s preserved in them. That’s what I do. And so, this particular type of microstructure that I see and that I’ve documented is very, very well documented now in younger rocks and not at all controversial in the younger rocks. The material I’ve identified identical to the younger stuff, so I mean it’s almost a no-brainer.

Interviewer: Nick Petrić Howe

Robert too thinks that sponge is the most likely conclusion.

Interviewee: Robert Riding

Let’s go for 99.9% because I can’t tell you what the difference is. The only difference I know is in age. Otherwise they look identical. So, I’m really very strongly convinced.

Interviewer: Nick Petrić Howe

Everyone I spoke to for this story did agree, however, that there will be a debate regarding this finding. But that could stimulate more research to try and track down animals’ early ancestors. In fact, they seemed mostly enthusiastic about this. After all, scientific debate can be a great catalyst for discovery.

Interviewee: Elizabeth Turner

By proposing this identity for a material this old, I’m already putting myself into an area of rather pronounced controversy. There are people who really won’t like this and that’s fine. I’m just throwing it out there, folks. Discuss, right?

Host: Noah Baker

That was Elizabeth Turner from Laurentian University in Canada. You also heard from Robert Riding from the University of Tennessee, Knoxville in the United States and Rachel Wood from the University of Edinburgh in the UK. You can read more about this discussion in the paper published this week in Nature. We’ll put a link in the show notes. And Nick has been very busy – there’s also a video all about early animals that has gone on our YouTube channel. Check the show notes for that too.

Host: Benjamin Thompson

Coming up, we’ll be heading to Greenland to hear about a researcher’s unconventional attempts to eavesdrop on a glacier. Right now, though, it’s time for the Research Highlights, read by Shamini Bundell.

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Shamini Bundell

Getting buzzed on caffeine has been shown to improve learning in bees. Bees are known to like caffeine, and they’ll actively seek out caffeine-containing nectar. But now, researchers in the UK have shown that caffeine can boost bee learning, helping them to remember and find certain kinds of flower to get a reward. The team taught bumblebees in a nest to associate a particular strawberry-like smell with a delicious sugar solution. Then they let the bees roam free in a room with different-smelling fake flowers to see which ones they visited first. Bees who’d had caffeine added to their sugar solution learnt the association better and were more likely to head straight to the strawberry-smelling flowers. This result supports the idea that caffeinated bees have better memories, and the findings could be used in agriculture to help train bees to visit certain plants and pollenate them. Sniff out the full research in Current Biology.

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Shamini Bundell

Archaeologists have reconstructed the last meal of an Iron Age man believed to have been ritually sacrificed 2,400 years ago. The incredibly well preserved body of the so-called ‘Tollund Man’ was found in a Danish bog in 1950. His gut contents were analysed at the time, revealing a last meal of porridge made from various kinds of seeds. But knowledge and research techniques have improved a lot since 1950, so scientists in Denmark decided to reanalyse the gut samples. They discovered that the meal included fish, that the porridge was cooked in a clay pot and that it probably contained water from a nearby lake or bog. They also found signs of several parasites, including tapeworm, whipworm and mawworm, which he probably got from consuming contaminated food or water. The exceptional preservation of the ‘bog body’, combined with the new techniques, provides an amazingly detailed glimpse into Iron Age life. If you’re hungry for more of that research, you can find it in the journal Antiquity.

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Interviewer: Benjamin Thompson

On 21 July 2019, in a fjord at the foot of the towering Bowdoin Glacier in northwest Greenland, a handful of people on two small boats lowered a heavy seismometer about the size of a small fridge into the sea. Equipped with an array of sensors, the probe descended 240 metres and anchored to the seafloor where glacier meets rock.

Interviewee: Evgeny Podolskiy

My colleague once told that it looks like Sputnik.

Interviewer: Benjamin Thompson

This is Evgeny Podolskiy, a glaciologist from Hokkaido University in Japan, describing his seismometer.

Interviewee: Evgeny Podolskiy

You drop it into water and then hope it will come back.

Interviewer: Benjamin Thompson

But no matter how hard you hope, things don’t always go according to plan. This is the story of Evgeny’s unconventional quest to eavesdrop on a glacier. He had a hunch that his measurements could offer new insights into our warming world, but getting to that point proved more difficult than anyone bargained for. But more on that later. First, some background.

Interviewee: Evgeny Podolskiy

If you want to know what is the future of ice discharged into ocean, you want to know the basal conditions, and this is the crux of glaciology, where a lot of effort is put because this is what we want to know but it’s very difficult to access.

Interviewer: Benjamin Thompson

Evgeny’s recent work has focused on Greenland, where the melting of vast ice sheets is set to have global consequences. Now, researchers often monitor the behaviour of glaciers by measuring seismic activity. But in such an inhospitable environment, that can be tough. From swirling Arctic winds to falling icebergs, isolating the right seismic signal can be very difficult.

Interviewee: Evgeny Podolskiy

It’s a ridiculously powerful seismic field and when these icebergs fall, we can recognise it 500 kilometres away on stations in Canada.

Interviewer: Benjamin Thompson

These events are so loud that they ruined US attempts to monitor underground Soviet nuclear tests during the Cold War. Evgeny wanted to find a way to cut through that noise and listen for the subtle movements of Greenland’s enormous ice sheet by tapping into seismic noise, not at the surface but at the base of the glacier. Often, though, that requires a lot of drilling, which can be difficult and dangerous. So, Evgeny had another idea.

Interviewee: Evgeny Podolskiy

So, the idea was why don’t we drop an ocean bottom seismometer, which is used by marine geophysicists and, in our case, if we could do that, we would be sitting in this quiet place, safe from these monster icebergs floating above us, without being touched and destroyed, and we will be listening, like eavesdropping, exactly on the surface on which this massive slab of ice is moving several metres a day.

Interviewer: Benjamin Thompson

Evgeny’s idea to drop a probe to the foot of the glacier seemed scientifically sound. But when it came to actually trying it out, well, that proved more challenging.

Interviewee: Evgeny Podolskiy

I was asked several questions by my colleagues like, ‘Do you have a port?’ ‘No.’ ‘Do you have a research vessel with a crane?’ ‘No, we don’t have.’ ‘Do you have electricity?’ ‘No.’ ‘Do you have technicians?’ ‘No.’ ‘Do you have permissions?’ ‘No.’ ‘And is it risky?’ ‘Yes,’ was my answer, and then, ‘Okay, let’s do it!’

Interviewer: Benjamin Thompson

Now, here is where Evgeny’s story takes a somewhat adventurous turn. He simply didn’t have access to the kinds of resources seismologists usually use to carry out readings on the ocean floor, so he had to get creative and garnered the help of some Inuit Greenlanders who know the area better than anyone.

Interviewee: Evgeny Podolskiy

I assembled this equipment with my hands in a hunter’s hut. We transported it by a little rubber boat to another fisherman’s tiny boat. We travel to the fjord and made final preparations next to the coast covered with whale blood because there is subsistence hunting in the area for narwhal, and then we make a very fast operation because we don’t want to experience this calving-generated tsunami which can happen at any time.

Interviewer: Benjamin Thompson

Mindful that skyscraper-sized icebergs could fall and overwhelm their tiny boat at any moment, Evgeny and his team of researchers and Inuit people lifted the probe into the water.

Interviewee: Evgeny Podolskiy

I slept so well after I dropped it because I was preparing for that day because it’s like assembling your own parachute because any bolt, any piece, if you make something wrong, you’re screwed.

Interviewer: Benjamin Thompson

With the seismometer at the bottom of the sea, Evgeny relaxed and returned to Japan. But his little probe was not out of the woods just yet. Sixteen days later, one of his colleagues went to retrieve it by playing an acoustic signal that causes the probe to release its anchor and return to the surface. But something went wrong. The probe didn’t heed the call and it was nowhere to be seen. A satellite phone call let Evgeny know the bad news.

Interviewee: Evgeny Podolskiy

I made my morning coffee and it no longer made me happy. I couldn’t drink it because this was a huge disappointment when it’s like all is lost and the most frustrating thing is that when this happens you have no idea what went wrong. People in oceanography lose sensors quite a lot and in the Arctic, some underwater sensors are destroyed by icebergs or something. It happens. The problem was that I have borrowed this instrument from a colleague of mine, so it’s not mine.

Interviewer: Benjamin Thompson

Not only did Evgeny have to tell his colleague that he’d lost their expensive probe, he also lost a trove of data – not a great day. But just when it seemed like all was lost…

Interviewee: Evgeny Podolskiy

It was a miracle.

Interviewer: Benjamin Thompson

Evgeny received word from some Inuit peoples several kilometres from where the probe should have resurfaced that brightened his mood.

Interviewee: Evgeny Podolskiy

They are looking for whales in this fjord, and they have incredible eyes to pick up things, to notice things, in the water. A hunter found our sensor in the open water. News spread and my colleagues could come and pick it up.

Interviewer: Benjamin Thompson

With the probe successfully retrieved, Evgeny could get to work analysing the data it had collected to look for the subtle seismic signal of the glacier rubbing against rock as it made its way to sea. And he found it and even used it to make some estimations of the glacier’s movement.

Interviewee: Evgeny Podolskiy

In our case, the glacier is making this rumble continuously. We can say how fast the glacier is moving by looking at seismic noise. How incredible is that. Because by listening to how loud things are, we can say it’s moving at 1.1 metres per day. There is a very nice correlation, which is one of the kind of key things we find, that we can see how fast the glacier is moving from the shaking of the coast around.

Interviewer: Benjamin Thompson

Of course, there are already a variety of different methods to measure glacier movement – radar, GPS, drone mapping and so on – but Evgeny says that his method offers some advantages, as the probe can be dropped off and left alone regardless of conditions on the surface. And he says that it could be used to gather other insights too – things like friction levels and water pressure at the base of glaciers.

Interviewee: Evgeny Podolskiy

The way glaciers move depends on these basal conditions, which we want to know to be able to represent them in models to predict sea-level rise in the next decades. The glaciers, they’re thinning. So, for example, our glacier at some point may detach from the base, so when this happens, to detect it is very difficult. So, with this kind of method I think we can see what are the impacts of this changing climate on glaciers.

Interviewer: Benjamin Thompson

For Evgeny, the discovery that glaciers produce a continuous detectable tremor as they slide confirms something that he suspected for years. Nevertheless, he says, the end of his quest has changed the way he perceives this often cold, inhospitable part of the world.

Interviewee: Evgeny Podolskiy

It’s mind-blowing to think that the Greenland coast is shaking at all times proportionally to the speed glaciers are sliding on their beds. Now, I stand there with a very different kind of feeling.

Host: Benjamin Thompson

That was Evgeny Podolskiy from Hokkaido University in Japan. You can find out more about his work on the Bowdoin Glacier in Greenland in a Nature Communications paper. We’ll put a link to that in the show notes.

Host: Noah Baker

And that’s all for this week. As always, you can reach out to us by email – we’re podcast@nature.com – or on Twitter – we’re @NaturePodcast. I’m Noah Baker.

Host: Benjamin Thompson

And I’m Benjamin Thompson. Thanks for listening.