We speak with andrew McCaig about the work going on to understand the origins of life and the geology under the seabed.
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Andrew Mccaig
Associate Professor of Geology at the University of Leeds
I'm joined by Dr Andrew McCaig, associate professor at the University of Leeds in the UK and his research focuses on structural geology tectonics and geochemistry. He was recently the co-chief scientist of the iodp Expedition #399: Building blocks of life, Atlantis Massif that sailed between April and June 2023.
It's mantle rocks which have been exposed on the sea floor that we drilled into. They've been exposed there by faulting. The previous record was 200.9 meters and we did 1268 meters, so we exceeded the previous record for drilling into mantle rocks by more than five times. So what are we recovering? We're recovering a drill core. It's about six and a half centimeters in diameter and what we got is very continuous sections of drill core so that the scientists can look at that in great detail as we move forward with post-cruise research.
and by getting deeper into the mantle Rock… I'm guessing exposed mantle Rock has started to change, started reacting with the sea water? is this a purer example of what's going on inside the planet?
Well, it's deep inside the planet, so the mantle rocks are not reacting with water certainly in the way that they are doing here. So the mantle is made of peridotite rock. And the main mineral in that is Olivine (typical mantle rocks are maybe 70% Olivine). At depth, if you're… let's say… down at 50 kilometers or something, that's very hot. The only place where water gets down to that depth is in subduction zones but we're at the Mid-Atlantic Ridge where basically the water only can only go down maybe a few kilometers. So what happens when these mantle rocks get exposed on the sea floor is that the water can get at them really easily and the the mineral Olivine alters to the mineral Serpentine. Serpentine you can think of it as a hydrated version of Olivine, it's got more or less the same magnesium and iron and silica in it, but it's got water added to it. And that process of serpentinisation is really interesting because in that process where the olivine alters to serpentine, it also forms magnetite and hydrogen gas.
That hydrogen gas is what we would call in our expedition (though some people might dispute this), the first building block of life. Then that hydrogen gas can combine with carbon dioxide which may be either from the ocean, or it may be deep seated carbon dioxide coming from deep in the Earth because the Earth is degassing a certain amount of carbon dioxide all the time. So this reaction between CO2 and hydrogen makes methane. We're all familiar with methane, that's what we burn on our cookers in order to cook our food. If we have a gas cooker, that's methane. Now most methane in the world is generated by biological processes: by animals. We've all heard about this in the context of climate change; that cows and sheep are eating grass and generating methane and that methane is contributing to global warming. This is the normal way it happens but here what we're seeing in the spensenisation process, is you're making methane by abiotic processes - by processes that don't require any microbes or that sort of activity. What we see as well, we see higher organic molecules like formic acid and acetic acid. So now the methane is combining with more water and so on it's making more complicated molecules. Finally, previous workers have detected some amino acids called tryptophan. Now this isn't one of the amino acids that's in DNA but if you can make amino acids without any biological activity, then is what you need to do in order to before you can possibly have life (if we believe in the evolutionary version of the origin of life).
Saturn’s icy moon: Enceladus, and it’s structure.
(Image courtesy of NASA)
So people are very interested in serpentinisation, and they're not just people who work on rocks in the Atlantic Ocean, people who work on the icy moons like Enceladus and Europa and so on. These moons have got icy surfaces and water underneath the ice and underneath that water is the same stuff as the Earth's mantle. We know from meteorites that most meteorites are made of essentially mantle rocks, they're the breaking up of planetary bodies which are similar to Earth. And so, the speculation is that just as microbial life might have evolved in places like the Atlantis Massif where sea water can interact with olivine-rich rocks, the same thing might indeed be happening on icy worlds up in the solar system. So it is a very interesting place the Atlantis Massif for astrobiology as well as for marine geology.
looking down to look up.
Indeed. But the other interesting thing about our whole expedition is that we also had on the ship microbiologists, and the microbiologists were collected a whole set of samples every five meters or so down this hole for the 1280 meters. We think that the bottom of the hole, it’ll be probably at more than 120 degrees. At the moment, what we've got is some temperature measurements which go up to just over 90 degrees, but just before we've done that we'd flush cold water into it for an extended period. We think that in a few years we'll be able to go back and measure the temperature and probably be above 120 at the bottom of the hole, which is above the current limit for life. So potentially, the microbiologists have got samples in these rocks where they find bacteria, microbes and things like that, which will be really exciting. Of course, we don't have any of that data yet.
yeah it's always frustrating. everyone wants the results when you come back to shore but it's like: that's a year, two years away, maybe. there's a lot of work to be done.
Exactly.
this is very close to an area we've discussed in the past, the Atlantis massif is is kind of next door to the lost city. it’s the same processes going on there isn't it?
Exactly, so the Lost City hydrothermal field is on the top of the fault line. It's only 800 meters away from the deep hole we drilled, so we're drilling into the substrate of Lost City. So the fluid that’s coming out of Lost City is more than 100 degrees. It's come from pretty deep down and it's gone through rocks similar to the ones we've drilled, so we can look at what's going on in there and we can hopefully make better constraints as to what's going on underneath lost city and where the hydrogen methane that is found in Lost City hydrothermal field is coming from.
and is that your particular area that excites you? the potential origins of Life?
Uh, that's not really my field at all. So the way that this whole thing started… I'm more of a petrologist and structural geologist, if you like… a geochemist to some extent. So I work for a long time on the shear zones in the Pyrenees, I was an on-land geologist and then I moved to kind of fault rocks in the ocean. So my interest in the Atlantis Massif has been historically mainly in the fault that exposed these peridotites and also gabbro rocks which are the lower crustal rocks.
Rock core from the expedition
(Image courtesy of Lesley Anderson/ IODP JRSO)
But, going back to what you asked about my expertise, so that the process of getting an expedition approved is quite a long one and it started in 2018. I just got together mainly with my petrological friends and said why don't we drill a deeper hole in the Atlantis massive that would be interesting. So we put together this proposal of deepening hole 1309 D. That was the original intention, this hole, five kilometers away in the gabbro and so we were going to deepen that. We were going to get down to places where the temperature was about over 200 degrees and look at reactions between water and rock that were going on down there. And then I realised that when you're getting one of these international expeditions funded, you need to have as broad a coalition of people as possible. Obviously I was interested in Lost City and and I've been a co-proponent of another Expedition #357 which drills shallow holes in the vicinity of lost city. And so I said: well, we weren't going to put microbiology in, because our hole was going to start at 104 degrees above the life line. So we thought: well, we'll sample waters in it. So the microbiologists are interested in the microbes that might be in the water. So I don't make this proposal by being an expert in everything. I know about the structural geology - I can write all that, but I get other people to collaborate who can do this. So it's a completely multi-disciplinary international team, scientists from different countries all over the world… Japan, China, India, Australia, Germany, France, America and Britain. So those are the all the countries that we had scientists on the Expedition. So um I think the IODP is an exemplary program, in this sense, because all the data is free of access after a year of monatorium. So anyone can go and interact with that.
on a previous episode we spoke with Mandy Joye about the Deep biosphere and the theory of how how deep life goes and how much there is. we’ve even spoke to Kevin hand about potential life on the ice moons and how much it felt like a deep sea habitat. we discussed that if you transplanted a hadal amphipod to enceladus's ocean, it might starve rather than die immediately, it might live long enough to run out of food.
It might yes. So, for the microbes in Lost City, they can't rely on photosynthesis for their food because there's no light. So they're chemosynthetic bacteria - they rely on chemical reactions to give them energy. We live off carbon which is is generated by microbial and biological activity. We eat plants, we eat animals, it's fixed into a form we can use it. And we don't try and get our carbon directly from carbon dioxide. But in the bottom of the ocean they need to get their carbon from somewhere else. Now of course, once you've got some microbes, the new microbes can eat the old microbes and so on. But in the early days of life, they had to be capable of getting their carbon from abiotic sources. So people are very interested in the microbes that still do that.
there was a record of previous microbial life as well isn't there? not just what's extant right now and living, but there were records of both the Earth's previous climate and life?
Well we can find in rocks, three billion year old rocks we can find stromatolites which are microbial mats. I'm getting out of my comfort zone now but you can certainly go back a reasonable way. So some of the microbiologists on our ship, they don't look at the microbes themselves they look at the fossil microbes, the organic matter that's left. They do DNA sequencing on it.
So we had an interesting different microbiologists onboard. We had Gordon Southern he's very interested in living microbes. He was finding microbes that were living off bits on the inside of the drill string, which is metal. They were growing from the iron oxidation, the rust basically. We have Feng Ping Wang who's from China and she's a very famous microbiologist and she specialises in culturing in the laboratory. So she's doing these things right at the limit of life, culturing them for many years and then seeing: ‘well, okay these microbes here have survived at temperature X. If I put them in temperature X-20 degrees then they grow.’ She collected lots of specimens which she's put into little pressure vessels and taken back to China to to do these experiments in her lab. So a very very interesting set of people, a really broad team.
so doing this required some old technology and some very new technology. you mentioned you revisited a hole that was bored previously and it was bored quite a long time ago. wasn't it was it about 20 years?
Uh yes in 2004-2005. We were there over Christmas and New Year, so yes it's been there for a long time. What we do with these holes, we put what's called a re-entry cone onto the top. There's a re-entry cone and some casing which just protects the top of the hole from bits of rock falling into the bottom. So we'd put this re-entry cone in back in 2005 and it's still there now and we were able to re-enter it. And now, we've left this new hole with a re-entry cone as well.
So hole 1309D, it was re-entered after seven years by an expedition called 340t which was just a logging expedition to measure the temperature. So they just lowered geophysical instruments down the hole with the drilling ship and measured the temperature which is really very interesting. Then it was left for another 13 years and we went back into it and sampled water in the hole to see whether in the intervening 13 years since it was last disturbed, we'd had reactions go on between water and the rock in the deeper parts of the hole. So we measured the temperature gradient and then we did deepen the hole by another 80 meters. So we've got some rock from down the bottom there as well including some samples from microbiologists so they can prove there's no life at 140.C degrees.
it's something that's just very easily said ‘we re-entered a hole that we had previously been drilled’ but these are over 2000 meters deep? you're on a moving platform way above them. how on Earth is that achieved?!
Well basically: we know the latitude and longitude of the hole so we take the ship to that latitude and longitude. So the ship the JOIDES Resolution, it's a 50 year old drilling ship, so in drilling-ship-terms it's pretty old-tech, you know. You can go on a tour around it and you can go in the shack where they control the drilling and it's got knobs and dials and things like that, you know those old school things that we used to have on instruments. Oh, and then they’ve got a crew of about five guys who are tripping the pipe, so it's a quite a labor intensive thing. Well on a modern oil field drilling ship, it's all pretty much robotic and it's all controlled from a dedicated computer in some place. Not very near the drill floor.
no one's getting muddy and wet…
No, exactly. Only if they have to fix something. But anyway, how do we find the hole? Well what we have to do is we don't have any submersibles or ROVs that can go down there and look for it. What we do is we just sit there on the top of the sea and we ‘trip the pipe’. That means that we first prepare the drill bit and what's called the ‘bottom hole assembly’. So, it's a drill bit that's about a foot across, but it's got this 6.5cm hole in the middle which is where the core comes up. So it's like a drill bit which can drill a hole in the rock, leaving a column of rock that pokes up through. Then it's got a bunch of rather heavy bits of pipe that give it a bit of weight at the bottom. Then above that is the drill string which is in 30 meter lengths. So they lower that down the moon pool (in the middle of the ship there's a big hole that's called the mood pool, that's where the drill and everything can go down through) and then they use the Derrick and a crane to pick up another 30 meter length. They screw that into the previous bit and then they drop that down, and so on and so on.
The moon pool onboard the JOIDES Resolution (Image courtesy of Tim Fulton/IODP JRSO)
So the 1309 D hole was actually at about 1600 meters below the sea floor, so you can work out how many lengths of pipe they had to put in there. So, 50-odd lengths of pipe to get down there. And then when you've got down to the right depth, you send a camera down. There's a frame that they can clip around the drill string and drop that through the moon pool. So you look on the camera for the drill bit and you can see fish and things swimming around. They just look around for the cone sticking up. I think the first time we entered it took about an hour perhaps to find it, and we're talking about something which is two meters across here, at 1600 meters depth. There's no very high tech in doing this, you know. Well, I mean the ship has a dynamic positioning ,which means it has a set of thrusters that can keep it stationary if the wind's blowing and so on.
I'm guessing there's a usbl on the on the end so you know where the the bit is relative to the ship
USBL (Ultra-short baseline):
USBL is a method of underwater acoustic positioning. A USBL system consists of a transceiver, which is mounted on a pole under a ship, and a transponder or responder on the seafloor, on a towfish, or on an ROV.
Um, not really. We assume it's directly below but if there's a current, it won't be directly below. The drill string has a certain amount of flex in it, and obviously we have a fibre optic link to the camera, that's the only electronics we have at the bottom of the the drill string. We were able to collect bottom water samples by a bottle on the drill string as well which is triggered electronically. But otherwise, it's not very high-tech at all really.
is the drill bit itself hydraulic?
No, the drill bit is turned from the top. But we were getting five meters of core in 1601c every hour and a quarter. So every hour and a quarter, a new set of core would come up for the core describers to describe. So they had a lot of work to do!
yeah that's loads of material! that's a quicker progress than I had in my mind.
Yeah, we were very surprised at the progress we got in this hole. I mean in hole 1309D we were going at about one meter an hour. But in terms of drilling rate, we were up at five or six meters per hour. So it was it was remarkably quick and trouble-free drilling compared to expectations.
so you weren't anticipating setting a new record? it just went extremely well?
Well, we were hoping to set some records in hole 1309D actually, so we just failed by about five meters. We decided when we got this such favourable Drilling in 1601c that we preferred that hole so we deepened that one because it's in the serpentinite and no one had done that before. We weren't expecting to beat the 200 meter record but we did.
yeah you've got to be flexible like that. you've just got to roll with the punches when you're out there.
Well absolutely yeah. We had a few punches of other sorts too.
can we talk about the history of this project and then maybe look into the future a little bit? because the idea of a of deep sea drilling began in the 1960s and there was a very successful project during that time and then funding dried out. it was a project that was Left for for a while and only quite recently has it reinvigorated. there's also a bit of uncertainty going forward isn't there?
Yes so it started as the Deep Sea Drilling Project. There were quite a lot of aims with the deep sea drilling project but one of the aims was to drill a hole through the moho (the moho is the boundary between the crust and the mantle). So underneath Britain or New Zealand it’s down at 30 kilometers or so, so it’s out of reach, really. The deepest hole as I recall is 14 kilometers from the Kola peninsula up in Northern Russia and there's been a couple of other deep holes as well in Germany and one recently in China. So drilling a hole in the moho in the continents is currently out of reach. So the idea was: well, in the oceans it's only six kilometers typically. So we can drill a mo-hole through this six kilometers and get into the mantle.
Mantle rock under polarised light. (Image courtesy of Alex Strekeisen)
So anyway, IODP was a really valuable program and one of the first things it did back in the 60s, they drilled holes from the mid-ocean ridge in the South Atlantic away from that and they basically proved that the age of the sea floor was progressively older as you went away from Mid-Atlantic Ridge. This was a critical proof of plate tectonics because the idea of plate tectonics had just come around. The idea that you had spreading ridges in the middle of the Atlantic and the Pacific where the new crust was being generated in a continuous process and therefore as you went towards Africa or towards South America away from the center of the Mid-Atlantic Ridge, the rocks should become older and older. And they did.
So that was a really key thing but now what's happened with the program is that the JOIDES Resolution is a 50 year old drilling ship and it's only got another five years of life in it before some environmental certificates and things run out completely. We've known for a long time that this drillship needed to be replaced in order to continue the program but of course replacing this drilling ship is an expensive thing and it's funded in America, it's an American ship funded by NSF (the research council in America that covers all branches of scientific research). The scientists from the IODP side had made proposals for a new ship, six-seven years ago and this kept being cut into the long grass by NSF “we will decide that later”. And then back in February, the expectation was that the program would be renewed for another four years and we'd have another four years of use of the JOIDES Resolution. But we had this rather bombshell announcement in the pages of Nature back in March this year that said that the NSF had decided that they were not going to continue the program.