New York, April 1:
A new research has revealed how the continents were formed on earth more than 2.5 billion years ago and how those processes have continued for the last 70 million years to deeply affect the planet’s life and climate.
Published online in Nature Geoscience, the study by an international research team of geoscientists 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.
Many scientists think that all of the planet’s continental crust — masses of buoyant rock rich with silica — 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,” said senior study author Esteban Gazel, an assistant professor of geology at Virginia Tech.
“We discovered that 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,” Gazel added.
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 travelling through the crust at velocities closer to the ones observed in continental crust worldwide.
The western Aleutian Islands and the Iwo-Jima segment of the Izu-Bonin-Mariana (IBM) arc system are some other examples of juvenile continental crust that has formed recently, the researchers said.
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 climate on the planet.
“We’ve revealed a major unknown in the evolution of our planet,” Gazel said. IANS