On the hunt for ancient reefs

CHRIS HATZIS
Eavesdrop on Experts, a podcast about stories of inspiration and insights. It’s where expert types obsess, confess and profess. I’m Chris Hatzis, let’s eavesdrop on experts changing the world - one lecture, one experiment, one interview at a time.

Dr Ashleigh Hood, lecturer at the School of Earth Sciences, University of Melbourne, is a geoscientist and reef hunter searching the globe for ancient reefs, which she believes host our ancient life forms and information about animal evolution. No longer in the oceans, these 500 million-year-old reefs are preserved high in mountains across Canada, Namibia and Australia.

The L’Oréal-UNESCO For Women in Science Program recognises the achievements of exceptional female scientists at different stages of their careers and awards them with Fellowships to help further their research. In 2019, four Australian Fellows were recognised at the annual awards ceremony and Dr Ashleigh Hood from The University of Melbourne was one of the recipients, recognised for her research in finding the earliest life forms in the Great Barrier Reef. She sat down to chat about her work with Dr Andi Horvath.

ANDI HORVATH
Are there still unanswered questions in Earth's evolution?

ASHLEIGH HOOD
Basically we don't really have much of an understanding of how life evolved on Earth from its origins all the way through to how did we get here, particularly in the early part of Earth's history. We also don't really know how that evolution of life is linked to environmental conditions on Earth, so things like climate change and oxygenation, big changes in the Earth atmosphere system.



ANDI HORVATH
Now you said you're a geologist. You're interested in sedimentary sort of layers.

ASHLEIGH HOOD

A sedimentologist is someone who studies the composition of sediments and how they interact so they form, I guess, ancient environments. I'm interested particularly in reefs, so I look at - I go into remote places in the world. I map out where these reefs are, so today, of course, they form the layers of the mountain ranges. These are not reefs that are any longer in the water, like the Great Barrier Reef. But we can walk along these ancient layers. We can figure out, by looking at the details in the rocks, exactly what sort of environment we're in. Was it a beach? Was it deep water? Was it in the area of the reef where today you would get all the corals, where the nice snorkelling is? We can figure this out by looking at the rocks in detail.



ANDI HORVATH
What's in these layers that attracts you?



ASHLEIGH HOOD
I'm particularly interested in rocks that are made of carbonate so limestones, for example. These are really exciting to me because they preserve exactly how organisms lived at the time that they were growing. For me this is hundreds of millions of years ago.

ANDI HORVATH
What sort of organisms are we talking about?

ASHLEIGH HOOD
I guess there's a range of different organisms that have evolved through time. In the particular time that I work on, we don't really know exactly what's going on. This is a period in Earth's history we have kind of a gap in evolution, so we see initially the evolution of very simple life so things like bacteria. Then at some point we get animals evolving so more complex life, more complex-celled organisms. The time that I look at in particular is right in-between this transition where we don't really know exactly what these organisms are.

ANDI HORVATH
Are they really peculiar? Can you describe some for us?

ASHLEIGH HOOD
Yeah, they are pretty weird. It's an ongoing mystery. The ones that we've been looking at in Australia are from the Flinders Ranges reefs and these are about 650 million years old. They live right down in the deep part of the reef, so these are not living like corals would live today right in the top. They're way down the bottom. They're maybe 200 to 800 metres depth so living in the dark. They look like little blobs, so they look like what you'd imagine a very primitive kind of sponge to look like. But they're not quite as complicated as a sponge, so we're talking about very, very simple organisms. But they're big. They're centimetres across. They make up these big cliffs which develop in the reef. Imagine you snorkel off the edge of a reef. You just look down and there's 800 metres of these strange blobby kind of things living in the reef.

ANDI HORVATH
Right, sort of minions of Sponge Bob.

ASHLEIGH HOOD
That's right, yeah. Yeah.



ANDI HORVATH

What role do they service in the ecosystem?

ASHLEIGH HOOD
These are the organisms which build the reef framework, so they're kind of taking the position in the ecosystem of what corals and what sponges would do today in the reefs. They're making these massive biological structures. How they feed and how they interact with the water, we don't exactly know. We think that they might do some sort of primitive metabolism, so they might just assimilate carbon from the water - because they're living in the dark, so they're not photosynthesising. They're living in probably very low oxygen conditions, but we think that this ocean water had a lot of dissolved carbon in it.

ANDI HORVATH
Do you see this all round the world? In other words, where have you toured the planet to see these Sponge Bob minions?

ASHLEIGH HOOD
Yeah, so I've been really lucky in my job that I've been able to travel a lot. In my PhD, I worked mainly in the Flinders Ranges but also in Namibia, in Northern Namibia in Africa, which was super exciting. We got surrounded by elephants one night when we were camping. Then more recently I've been up to Northern Canada where we got chased by bears, so very exciting things.

ANDI HORVATH
Tell us more about the elephants and bears. What did you do?

ASHLEIGH HOOD

It was terrifying. We were just camping out in this river valley, which was admittedly a foolish thing to do because that's where the elephants travel at night-time. We'd gone to bed in our tents. Herd of elephants came through. When I heard it, I didn't know what was going on, because all you can hear is them breaking branches of the trees as they're eating. There's maybe like 20 elephants all smashing down the forest. [You] can't hear them walking, because they don't make any sound when they walk. All you can hear as well is the growling of their stomachs, like digesting these trees, and so I thought they were lions. In my half-awake state, I thought they were lions. I got up and the only weapon I had in my tent was my boot, so I sat up in my tent with my boot for about an hour. Then eventually I drifted back to sleep as they moved on. But when we woke up in the morning, there were elephant prints all over the campsite, everywhere.

ANDI HORVATH
Right, not sure how you would have gone as boot versus elephant.

ASHLEIGH HOOD
Certainly not very well.



ANDI HORVATH
Not sure who would have come out better in that one. I think we can all guess. What about the bears? How did the bears attract your tent site? Did you leave food out somewhere?

ASHLEIGH HOOD

Yeah, so you get dropped in. We didn't leave it out, but it has to be somewhere. We kept it in buckets in a tent. In these mountains, they just drop you off in a helicopter, so you have to have everything with you. We had our food tent which was separate, of course, from the tents we were sleeping in. But one day when we were walking back from the field, we saw a little grizzly bear on the side of the hill. It looked little. It probably wasn't that little. The Canadian guys that we were with said, you know what? Don't worry about it. It's fine. It's just a bear. Us Australians were, of course, rightly nervous.

Then the next morning, we were just heading out for the day, just having our breakfast and heading out. Just maybe couple of hundred metres away just on this little tiny rock, someone said, oh, is that a boulder there? Is that a bear? When we said that, two bears stood up, so it was a mother and her cub, grizzly bears. It felt honestly like we were in a nature documentary. They were just watching us. They wouldn't leave. We tried to scare them off with bear bangers and stuff like that, but they vaguely walked away. We ended up having to leave, because we only had one gun. Of course, you don't want to shoot a bear. They were just going to come to our camp, if we left the camp for the day, and ruin the food and everything.

ANDI HORVATH

You just all quietly went your own way.

ASHLEIGH HOOD
Yeah, so we called the helicopter [and we're like], please help us.

ANDI HORVATH
Right. Get us out of here.

ASHLEIGH HOOD

Here.

ANDI HORVATH
Dr Ashleigh Hood, surely you get the philosophical question of why do we need to know the information about the gaps in the evolutionary puzzle that led to amazing life on Earth?



ASHLEIGH HOOD
I think this work actually addresses one of the most fundamental questions in science and that's how did we get here? This is, of course, a very big question. Part of it is more philosophy rather than science. But I think addressing the question of our history, of our human history and how we evolved from all different organisms all the way back through time, it's really important that we know this if we're going to know what we're doing in the future. It's like looking at human history. You want to have an understanding of history to know how you can apply those lessons in the future.



ANDI HORVATH
But I still can't quite connect it. We're talking from simple-celled organisms that become sponges. We're beyond that now.



ASHLEIGH HOOD
Hopefully. Hopefully we're slightly beyond that. Part of it is just pure science. Part of it is for the sake of advancing knowledge. The other part of it is we can use the geological record, in events like this evolution and events like environmental change, to tell us about what's going to happen in the future. For example, these reefs formed during a time called Snowball Earth, which is when the Earth froze over almost completely, twice. This is our most severe climate change in Earth's history and so right in the middle of this big ice age we see these huge tropical reefs grow. We know, for example, that animals potentially survived this climate change and so we can use examples like this from our history to learn about potentially how we're going to go with climate change in the future.

ANDI HORVATH

What surprised you in your industry so far?

ASHLEIGH HOOD
I guess there's been a huge amount of different ways that people can tackle these problems. I've been really surprised by how many different people are working on these kind of things. I'm coming at it from a geological perspective. I'm looking at the sediments. But there's people working on the biology of it, so how did the molecular clocks evolve? There's people working on it from a physical perspective. How far was the moon away to change the tides? How different was the world back then? I think it's only when everyone works together that we can really build up this really great picture of what this really bizarre, ancient Earth looked like.



ANDI HORVATH

One of the things that often boggles our minds is that we're talking a billion or 500 billion years ago, give or take a few billion. How is it that we understand that time is so deep?

ASHLEIGH HOOD
That's right. This is something that I think geologists take for granted a lot of times that we're talking millions or billions of years whereas the rest of the world works in years. I'm working on a period of time about a billion years ago to about half - 500 million years ago, sorry. But Earth's history spans back to about 4.5 billion. We really have a very limited record of what happened on Earth during these times, so we only get these tiny little slivers of rock that record one snapshot of time. The further you go back in time; the more fragmented things get. Having the perspective of having looked at the entire record is really the only way that you can put yourself into the position of thinking about time in the grandest sense.

ANDI HORVATH
As a geologist, do you have a favourite element on the periodic table?

ASHLEIGH HOOD
I have to say I probably do. I think magnesium's probably my favourite.

ANDI HORVATH
Oh, explain why.



ASHLEIGH HOOD
Most of the work that I've been doing, looking at these limestones, is actually made up of a mineral that's slightly different, so it's called dolomite. The difference between dolomite and limestone is that dolomite incorporates magnesium. A lot of the work that I've been doing has been trying to figure out the magnesium cycle in the past. Of course, today we use magnesium for a whole bunch of different applications, for fertilisers and stuff like that, but we think in the past that the oceans had a huge amount more magnesium in them than they do today as part of this changing chemistry through Earth's history.

ANDI HORVATH
There you have it, magnesium. I'll never look at it the same again…

ASHLEIGH HOOD
That's right.

ANDI HORVATH
...as I take it for a muscle relaxant.

ASHLEIGH HOOD
There you go.

ANDI HORVATH
Now does the information that you gather along with your colleagues actually help us perhaps think about the possibility of life on Earth elsewhere?



ASHLEIGH HOOD
I was working in the US on a NASA fellowship, which was part of the astrobiology team. The goal of our research was to look at Earth's history and how we would see Earth as if it were a planet elsewhere, so we looked at different parts of Earth's history. We tried to calculate what the atmospheric composition would be and what was living on Earth at that time. The idea is that our next step in technology with this astrobiology research is to have an instrument that can measure the atmospheres of exoplanets elsewhere. But the problem is we don't know on our own planet at which point in our evolution would we be able to detect that life was on our planet, so would we be able to detect very simple life like bacteria or is it only when trees and forests evolve that we would be able to see this signature? There's plenty of applications for understanding our own history to apply it to the universe.

ANDI HORVATH

In a few centuries' time, some cosmonaut or astronaut will be looking at your research going, oh, yes, look at - [then] we can see that happening on this alien planet.

ASHLEIGH HOOD
Hopefully.

ANDI HORVATH
That would be lovely. Now tell us about the L'Oréal-UNESCO For Women in Science Award. You were awarded that in 2019.

ASHLEIGH HOOD

I was really lucky to be chosen for that award. It's really helped me get my science out there. The goal of the award is to generally promote women in science and make women more visible in science, not only within their own community but also to the general public. For me this L'Oréal-UNESCO For Women in Science Award has allowed me to get out there and do things like this program, talking about my work, whereas previously I was kind of a typical scientist and would only publish in journals and talk in my own setting. For me it's been really valuable to get my science out there. I think broadly this award really helps just women be more visible in science. That's what we want going into the future.

ANDI HORVATH
I have to comment on the bag you've brought in to the studio. One of my favourite animals, because I used to like to have a favourite animal…

ASHLEIGH HOOD
Yeah.

ANDI HORVATH

...[every year], is the blue-footed booby which lives on the Galapagos Islands. You've got a bag with a cartoon of them on. How come you've got a Galapagos bag with one of my favourite animals?

ASHLEIGH HOOD

It's actually one of my favourite animals too. It's my favourite bag.

ANDI HORVATH
We're instant friends.

ASHLEIGH HOOD
That's right. Yeah, so I was lucky enough to travel to the Galapagos a couple of years ago with a group of friends. We just got to go on a boat and travel round the islands and look at all the different lifeforms that exist on these islands so the birds, the iguanas, all sorts of things. For me it was really exciting from a scientific background, because this is where Darwin developed the Origin of Species and this kind of stuff. But even more so, it was just an absolutely beautiful place to go.



ANDI HORVATH
Is it true that the animals aren't frightened of you?

ASHLEIGH HOOD
That's right, yeah. You can just walk around and they're not fussed at all. You almost have to be careful where you're stepping actually, because there'll just be a giant albatross or something in the way.



ANDI HORVATH
Really? Well, I must admit the blue-footed boobies have nice shoes.

ASHLEIGH HOOD
Certainly do.



ANDI HORVATH
Ashleigh, you're really passionate about what you do. Who got you started in this field? Where did this passion for geology and finding clues to unusual problems come from?

ASHLEIGH HOOD

I guess this came from several different points, so when I was just a kid, my grandpa actually used to take me on walks. I used to find rocks and put them in people's letterboxes, so that was the start of my love affair with geology.

ANDI HORVATH
Why did you put them in letterboxes?

ASHLEIGH HOOD

I actually honestly have no idea, but apparently I used to love doing it, finding shiny things and giving them also to other people down the street.

ANDI HORVATH

Fair enough. Do you still do that? Do you post rock samples?

ASHLEIGH HOOD

I still post rock samples.

ANDI HORVATH
Okay.

ASHLEIGH HOOD
That's right.



ANDI HORVATH
Not randomly but for professional purposes.

ASHLEIGH HOOD
That's right. That's right, mainly.

ANDI HORVATH
Got you. Okay.

ASHLEIGH HOOD
That was the start point. I've always been really interested in the natural world, so my parents used to take me camping a lot. We went rock climbing and we were always outdoors. Then I was one of the weird people, I guess, that always wanted to do geology. Often people get sucked into geology because they like the fieldwork or they think it's fun. I always knew what I wanted to do, what field I wanted to be in, but I didn't know which aspect of geology I was most interested in. But when I did my honours year - it was with one of the professors here, Malcolm Wallace - he showed me these reefs that he'd found in the Flinders Ranges. I got really, really excited about them and so that's where my PhD and the whole rest of my research has stemmed from.

ANDI HORVATH

What do we know about these reefs that we didn't know before?



ASHLEIGH HOOD

Before, no-one knew that they were even there. They thought that maybe there was just some limestones made of stromatolites which are the most common lifeforms back in the day. But when Malcolm and his students found these reefs [initially in] the first time, they discovered that these are massive reef complexes. These are bigger than the Great Barrier Reef. These are 20 kilometres long. The margin is a kilometre high. They are made up of really, really unusual frameworks. We don't know what the creatures are that live in there, but we think they might be a link between two different worlds, the world of simple life and the world that we live in today. I think we know a lot more now about the environment and about the organisms themselves.

ANDI HORVATH
They are the clues to the past. They are the clues of the combination of life, organic molecules interacting with each other, cells interacting with each other and, of course, the climate.

ASHLEIGH HOOD

That's right. Exactly.

ANDI HORVATH
Wow. That's life itself.

ASHLEIGH HOOD
Yeah, that's right. It's super exciting.

ANDI HORVATH

Dr Ashleigh Hood, you have the opportunity here to take the soapbox and profess to the public about what you'd like them to think about. Next time they see sedimentary layers, what is it that you'd like them to remember?

ASHLEIGH HOOD

I'd like everyone to think about the rock record from the standpoint of a detective, so I'd like next time everyone goes out and sees some rocks in the field to think, gee, I wonder how they got there. I wonder what ancient history that these rocks are telling us. I think once people start thinking more about just general excitement about where we came from, about how the Earth has changed, it's really going to help with putting our minds in perspective for how we're going to keep our planet in future.

ANDI HORVATH
Dr Ashleigh Hood, thank you.

ASHLEIGH HOOD

Thanks very much.

CHRIS HATZIS
Thank you to Dr Ashleigh Hood, geoscientist, reef hunter and lecturer at the School of Earth Sciences, University of Melbourne. And thanks to our reporter Dr Andi Horvath.

Eavesdrop on Experts - stories of inspiration and insights - was made possible by the University of Melbourne. This episode was recorded on December 4, 2019. You’ll find a full transcript on the Pursuit website. Audio engineering by me, Chris Hatzis. Co-production - Silvi Vann-Wall and Dr Andi Horvath. Eavesdrop on Experts is licensed under Creative Commons, Copyright 2020, The University of Melbourne. If you enjoyed this episode, review us on Apple Podcasts and check out the rest of the Eavesdrop episodes in our archive. I’m Chris Hatzis, producer and editor. Join us again next time for another Eavesdrop on Experts.