UW Researchers Contribute to Continent

An international research team, including University of Wyoming Professor of Geophysics Steve Holbrook and current and former UW graduate students, has revealed information about how continents were generated on Earth more than 2.5 billion years ago — and how those processes have continued within the last 70 million years to profoundly affect the planet’s life and climate.

Published online Tuesday in Nature Geoscience, the study details how relatively recent geologic events — volcanic activity 10 million years ago in what is now Panama and Costa Rica — hold the secrets of the extreme continent-building that took place billions of years earlier.

The discovery provides new understanding about the formation of the Earth’s continental crust — masses of buoyant rock rich with silica, a compound that combines silicon and oxygen.

“Without continental crust, the whole planet would be covered with water,” says lead author Esteban Gazel, an assistant professor of geology with Virginia Tech University’s College of Science, in a Virginia Tech media release. “Most terrestrial planets in the solar system have basaltic crusts similar to Earth’s oceanic crust, but the continental masses — areas of buoyant, thick silicic crust — are a unique characteristic of Earth.”

Joining Gazel in the research were Holbrook, former UW Ph.D. student Erik Everson and current Ph.D. student Jorden Hayes of Richland Center, Wis. Hayes is the second author of the paper.

“The generation of continental crust has been a long-standing mystery in Earth science,” Holbrook says. “Our study represents the first time that the signatures of continental crust — both geophysical and geochemical — have been observed in an active volcanic arc.”

“This research is really exciting because crustal genesis has systematic implications for nearly every other period of Earth's history,” Hayes says. “As a geophysicist, it is highly rewarding to see our geophysical interpretation corroborate with geochemical observations.”

The continental mass of the planet formed in the Archaean Eon, about 2.5 billion years ago. The Earth was three times hotter, volcanic activity was considerably higher, and life was probably very limited.

Many scientists think that all of the planet’s continental crust was generated during this time in Earth’s history, and the material continually recycles through collisions of tectonic plates on the outermost shell of the planet.

But the new research shows “juvenile” continental crust has been produced throughout Earth’s history.

“Whether the Earth has been recycling all of its continental crust has always been the big mystery,” Gazel said. “We were able to use the formation of the Central America land bridge as a natural laboratory to understand how continents formed, and we discovered while the massive production of continental crust that took place during the Archaean is no longer the norm, there are exceptions that produce ‘juvenile’ continental crust.”

The researchers used geochemical and geophysical data to reconstruct the evolution of what is now Costa Rica and Panama, which was generated when two oceanic plates collided and melted iron- and magnesium-rich oceanic crust over the past 70 million years, Gazel says. Melting of the oceanic crust originally produced what today are the Galapagos Islands, reproducing Achaean-like conditions to provide the “missing ingredient” in the generation of continental crust.

The researchers discovered the geochemical signature of erupted lavas reached continental crust-like composition about 10 million years ago. They tested the material and observed seismic waves traveling through the crust at velocities closer to the ones observed in continental crust worldwide.

Additionally, the researchers provided a global survey of volcanoes from oceanic arcs, where two oceanic plates interact. The western Aleutian Islands and the Iwo Jima segment of the Izu-Bonin islands are some other examples of juvenile continental crust that has formed recently, the researchers say.

The study raises questions about the global impact newly generated continental crust has had over the ages, and the role it has played in the evolution of not just continents, but life itself.

For example, the formation of the Central American land bridge resulted in the closure of the seaway, which changed how the ocean circulated, separated marine species, and had a powerful impact on the planet’s climate.

“We’ve revealed a major unknown in the evolution of our planet,” Gazel says.

Other researchers involved in the project include the GEOMAR Helmholtz Center for Ocean Research in Kiel, Germany, the Lamont-Doherty Earth Observatory of Columbia University, Simon Fraser University in Canada, Rutgers University and the University of South Carolina.