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Plate tectonics key to life on Earth?

Tectonic plates. Courtesy US Geological Survey

Tectonic plates. Courtesy US Geological Survey

Is our vital blue planet the last of its kind?  Or has it always been one of a kind?  From the perspective of post-modern geologists, planet Earth is like no other solar body yet discovered.

“I think when you live on the Earth, you take it for granted,” says Katie Cooper, who thoughtfully considers such esoteric questions for a living. As one of a relatively new group of geologists who use computer simulations to study the thermal and tectonic evolution of our planet, her viewpoint is decidedly celestial.

Cooper, assistant professor in the School of Earth and Environmental Sciences, studies the broad area of geodynamics—particularly the evolution of Earth as a planetary system. Specifically, she models how the three main layers of our planet—core, mantle, and crust (lithosphere)—interact and change over time.

“I look at the Earth as a giant heat engine which drives all of the geologic activity we see at the surface,” she says. “In the past, the core was hotter than it is today. The planet is slowly cooling and that affects everything on the lithosphere.”

That cooling takes place in large part through thermal convection. Like boiling water or the slow movement of oil blobs in a lava lamp, hot plastic rock from the Earth’s mantle is constantly rising toward the surface, where heat and energy are released in hot springs, earthquakes, or volcanic eruptions. At the same time, cooler rock is sinking toward the interior core.

This steady interplay leads to the phenomenon of plate tectonics where vast puzzle-like sections of Earth’s crust “float” on top of hot rock in the mantle—and imperceptibly migrate across the globe.

Earth stands alone

Although plate tectonics is often taken for granted as standard planetary modus operandi, it turns out that Earth is a world apart from other planets.

“Plate tectonics is unique to Earth as far as we know right now,” says Cooper. “The big question is if this is unique to our solar system? Our galaxy?  The universe?”

Not only unique, but possibly essential to life itself. Through its part in cooling the planet’s interior, plate tectonics allows Earth to maintain a magnetic field that shields our world from dangerous solar radiation and, in effect, creates a safe haven for life to flourish. Which presents Cooper with another question—did plate tectonics create optimal conditions for the initial occurrence of life?  No one knows for sure.

Plate tectonics—the next generation

For the first half of the twentieth century, geologists suspected that Earth’s continents had once formed a single land mass before breaking up and drifting aimlessly apart. The continental drift hypothesis was backed up by fossil evidence but no one could explain the actual physical processes driving it.

That changed in 1963, however, when Princeton professor, Harry Hess, used WWII submarine-hunting technology to discover unusual magnetic polarity in the ocean floor. It was concluded that hot rock from the mantle was rising up through the lithosphere and pushing the sea floor—and the continents on either side—apart.

This finding provided the mechanism to explain the purposeful movement of Earth’s plates and led to the development of the first theory of plate tectonics.

Today Cooper is among a new generation of geologists who study what could be called “post” plate tectonics. Taking the field up a notch, she investigates similar processes on other planets and asks why Earth has plate tectonics in the first place.

“Is it the preferred mode of operation?” she asks. “Does it help the planet lose heat most efficiently? Is it a coincidence?”

Using a computer cluster of 600 processors working together as a single unit, Cooper attempts to unlock these mysteries by crunching enormous calculations that often run days or weeks to generate results.

Doing these “paper and pencil calculations” as she refers to them, Cooper builds computer models of planets and applies basic laws of physics to see if the theories are applicable.

Free water and stagnant lids

Geological map of the Pacific Northwest. Courtesy US Geological Survey

Geological map of the Pacific Northwest. Courtesy US Geological Survey

One theory being investigated is the idea that Earth is unique due to the presence of free water on the planet surface.

“Water lubricates the fault lines and helps rock masses glide, which allows an active overturning of the Earth’s crust,” she says. “But, since we’ve seen evidence that Mars once had free water, it raises more questions … there must be a lot more to it than just this. We may be missing some aspects.”

Other solar bodies do show variations of Earth’s tectonic plate and convection system, she reports. For example, Mars and some asteroid bodies have a “stagnant lid” design where hot rock can churn deep inside the planet but nothing seems to happen at the surface.

Venus is speculated to perhaps have an “episodic overturn” model where the entire planet surface crumbles and sinks down into the interior while massive amounts of magma rise to the surface to replace it.  In either case, the processes continue until  the celestial body has used up all of its energy and eventually “dies.”

Is anyone out there?

Although the field of post plate tectonics is still in its infancy, Cooper believes the future of the specialty lies in taking models known to be physically possible and collaborating with field geologists to determine if they are Earth-possible.

Through their measurements and observations, “our colleagues might say, ‘this just doesn’t work for Earth, but could it work for another planet?’ It’s critical to gain a better understanding of how our Earth operates, especially as the human race reaches out to explore the solar system,” she stresses.

Indeed, just as Cooper looked out her window as a young girl and wondered how the mountains and canyons came to be, her curiosity now twists and turns the Rubik’s cube of life forms, plate tectonics, and Earth’s style of mantle-driven convection.

“The more we learn about these processes,” she says, “the more likely it is that mankind will someday discover other planets and celestial bodies capable of hosting life.”