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ERIK KLEMETTI03.28.11 9:16 AM
SCIENCE
Drilling into the planet: Why we want to sample the mantle (and why we already have)
I’ve had multiple discussions with colleagues of mine in the geosciences on why we can’t seem to capture the public’s attention/fascination like our neighbors in the sciences – physics and astronomy (and for me, literal neighbors in the same building). When you think of the prominent, publically-identifiable personalities or projects in the last 50 years, […]
I've had multiple discussions with colleagues of mine in the geosciences on why we can't seem to capture the public's attention/fascination like our neighbors in the sciences - physics and astronomy (and for me, literal neighbors in the same building). When you think of the prominent, publically-identifiable personalities or projects in the last 50 years, most of them are have to do with space or cosmology (the origin of the universe) - and they get the big bucks to fund things like the Hubble Space Telescope or the Large Hadron Collider. A lot of our conversations seem to center on the idea that geoscientists don't tend to "think big" when it comes to projects, and many times, we are content to stake out our little piece of the planet or our own isotope or what have you without trying to think what project might be truly captivating to the public. Surely, no one is making a calendar of the best trace element plots of each year, that is for sure. So, how can the geosciences "think big".
One idea is to do to the Earth was Apollo did to the Moon - that is, to go boldly* where no man (or drillbit) has gone before: the mantle. As much as we talk about the interior structure of the Earth, almost all the evidence of what exactly is down there is purely circumstantial: a coughed up chunk here, a seismic wave there, a change in gravity, maybe if we're lucky some scraped up mantle junk stuck to the bottom of an oceanic plate. Beyond that, we have barely scratched the surface of the planet, literally. The deepest drillhole ever made on the planet was the Soviet Kola hole (however, the longest reach of any drillhole is the Odoptu OP-11 well), and that reached a whopping ~12 km down in continental crust, whose average thickness is 35-55 km (and as thick as 70 km in some places). To look at it a different way, the Kola hole drilled down ~0.19% of the distance from the surface of the Earth to the middle of the inner core - like taking a pin and sticking it 0.2 mm into your average orange (yes folks, we're merely zesting the Earth). So, to make a long story short, not far.
We have barely zested the Earth.
Now, if you are in the business of drilling into the Earth, a hardy continental plate isn't exactly the place to start. I mean, as I said, the crust tends to be thick, at least compared to the other tectonic plate, the oceanic variety. The oceanic plates tend to be thinner, average ~7 km thick (so the combination of their relative thickness and density mean they sit lower than continental plates, allowing for the ocean basins they typically create), so if you want to drill into another layer of the Earth beyond the crust, an oceanic plate is where to start. This is exactly the thinking of a project in the 1950-60s called Project Mohole that sought to drill through an oceanic plate into the mantle, the next layer down.
