01/22/2016

Digging Deep Into the Crust of the Earth

7:22 minutes

Gabbro crustal core sample brought up by the Joides Resolution Indian Ridge Moho expedition. Photo courtesy of JOIDES Resolution
Gabbro crustal core sample brought up by the JOIDES Resolution Indian Ridge Moho expedition. Photo courtesy of JOIDES Resolution

In his classic tale Journey to the Center of the Earth, author Jules Verne dreamed of reaching the center of our planet through volcanic tubes. In the 1960s, scientists took up that challenge and tried to drill down into the earth’s mantle, but abandoned the project due to a lack of funding. Now, a team of scientists aboard the research vessel JOIDES Resolution is working to bore a hole deep into the Atlantis Bank in the Indian Ocean to collect samples of the crust and eventually break through into the mantle. Geologist Henry Dick, co-chief scientist of the expedition, joins Ira for an update on the progress of the project and explains what these samples could reveal about the formation of the planet.

Segment Guests

Henry Dick

Henry Dick is a Senior Scientist in the department of Geology & Geophysics at the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow.

One of the first games you probably played in your backyard was how deep you could dig a hole. Start out, you fling out dirt and rocks with your plastic shovel. And if you dig long enough, inevitably some wise guy’s going to come by and say, have you reached China yet?

Well, my next guest has taken that whole digging challenge to a new level. He joins us aboard the research ship JOIDES Resolution, way out in the middle of the Indian Ocean. The expedition has been drilling since December, trying to dig through to the crust of the earth. Henry Dick is a geologist and co-chief scientist of that expedition on the boat there. Hopefully, we can bring him in. Welcome to Science Friday. Henry?

HENRY DICK: Nice to be able to talk to you, Ira.

IRA FLATOW: How far have you gotten in this project?

HENRY DICK: Can you hear me?

IRA FLATOW: Yes, I can. How far have you gotten in the dig so far?

HENRY DICK: We’re about a half mile down and drilling ahead. Unfortunately, we’re going to be coming to an end of our cruise in about 10 days, so we’re going to have to leave here and hope we come back soon.

IRA FLATOW: And what is the point of all of this?

HENRY DICK: Well, there are several major points, the first of which is that the ocean crust comprises 2/3– no, sorry, 3/5 of the Earth’s crust. And yet in all that crust, most of it is lower crust, and we only have two holes into it, one in the Atlantic and one into the Indian Ocean, that are of any significance at all. And we haven’t drilled more than about a third of the way through it. And when you’re talking about the composition of 3/5 of the Earth’s crust, that’s kind of a big gap in our learning.

IRA FLATOW: I remember back when I was a kid in the early ’60s, there was something called Project Mohole.

HENRY DICK: There certainly was. And this is really an outgrowth of it. And one of the two guys who really dreamt up that is one of my heroes, Harry Hess. And he proposed that the Moho, which is the first major seismic discontinuity beneath the crust– which many people think is the boundary between the crust and the mantle– he proposed that it was an alteration front.

The mantle rising up in the oceans, for example, would undergo alteration with contact with sea water and produce rock of lower velocity. And they were actually looking at low-velocity rock lying on high-velocity rock, both of mantle origin.

It fell out of favor, but since we’ve been working here in the Indian Ocean now for the last 15 years and up on the Gakkel Ridge. We’ve discovered that large parts of the sea floor have no crust. The mantle is directly exposed to the sea floor.

And that has revived the idea that we do have crust in these oceans, but the actual seismic discontinuity is an alteration front due to sea water sinking in through the crust and into the mantle.

IRA FLATOW: Wow, that’s cool. That’s very interesting. Is there any possibility that way down– you’re now a half mile and still drilling. There’s life down there in the rocks.

HENRY DICK: Well, we’ve got a couple of biogeochemists on board who are busy assaying the rocks for microbes and fungi and other things. And they do find a few. But the hope is that– well, the thought is that if we have a lot of altered mantle rock down there, that creates hydrogen gas, which in turn reacts with seawater to form methane.

And bugs can live off of methane. And we’re thinking that there may be a hidden planetary biosphere beneath the earth’s crust out in the oceans.

IRA FLATOW: I know when I use my Craftsman drill bits at home, after a few drills through a piece of steel, the drill bit is basically wasted. How many drill bits do you go through so far?

HENRY DICK: We go through a drill bit every 40 hours. They cost about $16,000. And they are about– oh, about eight inches in diameter. And they have tungsten carbide roller cones on them that bang into the sea floor. You rotate it just like an oil drilling bit, except for it’s hollow in the center so we can pull up cores. And on top of that, we have about 75 tons of steel pipe.

IRA FLATOW: Wow. Now, that brings up the point that oil drilling companies are always drilling holes in the ocean. How is your drilling different than what they do?

HENRY DICK: Well, they’re out in sedimentary formations. They’re looking for oil. And we’re looking– we’re starting in the basement rock on the– well, not in this case– the basement rocks from the lower crust.

We actually are in a place where the shallowest layers were stripped off tectonically. And this was a huge advantage because the shallow layers are the hardest to drill through. And we are drilling right into a rock known as gabbro, which is the remains of mid-ocean ridge magma chambers.

IRA FLATOW: And so how far do you think you can get before you have to come home?

HENRY DICK: We’re thinking that we’re going to get another 100 meters. So we’ll be down about 850 meters. We think in meters, you know.

And we will come back here hopefully in the next two years– if not then, in the next four or five years– for another leg where we hope to drill an additional mile.

We’ve got the whole setup, which is quite a trick, setting up. You have to set up a drill cone so you can get back in the hole and drill it into the hard rock. And then you bore on down, and it’s going to take at least two of these expeditions, and possibly three, to get through the crust and into the mantle.

IRA FLATOW: So you’re not afraid that the Earth or the rock is going to shift a little bit and close the hole up or make it impossible to go back down through that same spot?

HENRY DICK: I’m very sorry. We had an interruption here. Could you repeat that?

IRA FLATOW: Yeah. You’re not fearful that when you give up on this hole and go home that it might not close up or the Earth’s crust or the rock might not shift and close– make it more difficult to get back into–

HENRY DICK: Well, that’s an interesting question because we’d moved the hole from where our test core was. And we ran into immediately worse conditions. And the reason we moved it is we wanted to see how the crust varies.

And we ran right into a fault zone, and that slowed us down. And so there is an area at the top of the hole with a lot of loose rock. And we lost a bit of a drill bit in it, which then fell down later on deeper in the hole. And we found ourselves really on top of it so we get no core.

And this is one of the problems with hard-rock drilling is it’s very risky. And so what we’re going to do is we’re going to actually pump some cement into the top of the hole where that interval was. It’ll go into the formation and lock it up. When we come back here, it’ll be pretty easy to drill through that cement and continue drilling on down.

IRA FLATOW: Well, we wish you luck, Henry, and safe travels and good luck in finishing your project.

HENRY DICK: Well, thank you.

IRA FLATOW: Henry Dick is a–

HENRY DICK: We’re excited.

IRA FLATOW: Yeah. Henry Dick is a geologist based out of Woods Hole Oceanographic Institute there on the boat in the Indian Ocean.

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