Cooper, with lava lamp, in her office.
Purple blobs of oil rise lazily through pink water, gracefully skirting other blobs on their way back down. Quietly convecting on shelves and in corners of dusty offices, the lava lamp has become an essential metaphor for geophysicists everywhere – a symbol of post-modern geology.
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,” said 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 that drives all of the geologic activity we see at the surface,” she said. “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 often is taken for granted, 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,” said Cooper. “The big question is, ‘Is unique to our solar system? Our galaxy? The universe?’ ”
Not only unique, but possibly essential to life itself. Through its role 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 20th century, geologists suspected that Earth’s continents had once formed a single land mass before breaking up and drifting 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 apart the sea floor – and the continents on either side.
This finding provided the mechanism to explain the purposeful movement of Earth’s plates and led to 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. 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 asked. “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,” Cooper builds computer models of planets and applies basic laws of physics to see if the theories are applicable.
Free water and stagnant lids
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 said. “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 show variations of Earth’s tectonic plate and convection system, she said. For example, Mars and some asteroids 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 uses 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 its future 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?” she asked. “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.
”The more we learn about these processes,” she said, “the more likely it is that mankind will someday discover other planets and celestial bodies capable of hosting life.”