Modern plate tectonics emerged roughly 3.6 billion years ago, say scientists who studied zircons from Jack Hills of Western Australia. Photo by Dustin Trail/University of Rochester
May 14 (UPI) -- Modern plate tectonics, a defining feature of Earth and its unique ability to support life, first emerged roughly 3.6 billion years ago, according to research published Friday by the journal Geochemical Perspectives Letters.
The analysis identified zircons, the oldest mineral on the planet and a source of the metal zirconium, that date back 4.3 billion years, the data showed.
This means these nearly indestructible minerals formed when the Earth was only about 200 million years old.
Along with other ancient zircons collected from the Jack Hills in western Australia, spanning Earth's earliest history up to 3 billion years ago, these minerals provide the closest thing to a continuous chemical record of the developing planet, researchers said.
After analyzing the results of the hundreds of useful zircons from among the thousands tested, there was marked increase in aluminum concentrations roughly 3.6 billion years ago, which may be when the planet's tectonic plates began to form.
"We are reconstructing how the Earth changed from a molten ball of rock and metal to what we have today," study co-author Michael Ackerson said in a press release.
"In a way, we are trying to answer the question of why Earth is unique, and we can answer that to an extent with these zircons," said Ackerson, a research geologist at the Smithsonian's National Museum of Natural History in Washington, D.C.
Earth is the only planet known to host complex life and that ability is partly predicated on plate tectonics, according to Ackerson and his colleagues.
No other planetary bodies known to science have Earth's dynamic crust, which is split into continental plates that have moved, fractured and collided with each other for eons, the researchers said.
Plate tectonics create a connection between the chemical reactor of Earth's core and its surface that has engineered the habitable planet people enjoy today, from the oxygen in the atmosphere to the concentrations of climate-regulating carbon dioxide, they said.
However, when and how plate tectonics began has remained mysterious, according to the researchers.
For this analysis, Ackerson and his colleagues collected 15 grapefruit-sized rocks from the Jack Hills and reduced them into their smallest constituent parts - minerals -- by grinding them into sand.
They tested more than 3,500 zircons, each just a couple of human hairs wide, by blasting them with a laser and then measuring their chemical composition with a mass spectrometer to determine their age and underlying chemistry.
Of the thousands tested, about 200 were fit for study due to the ravages of the billions of years these minerals endured since their creation.
A zircon's age can be determined with a high degree of precision because each one contains uranium, which, with its radioactive nature and well-known rate of decay, allows scientists to reverse engineer how long the mineral has existed.
After analyzing the results of hundreds of useful zircons from among the thousands tested, there was a marked increase in aluminum concentrations roughly 3.6 billion years ago, the researchers said.
One of the few ways for high-aluminum zircons to form is by melting rocks deeper beneath Earth's surface, according to the researchers.
Their age could roughly pinpoint the time at which the Earth's crust was getting thicker and beginning to cool and that the formation of modern plate tectonics, the researchers said.
The study is part of the Smithsonian's Our Unique Planet initiative, a public-private partnership that supports research into some of the most enduring and significant questions about what makes Earth unique, according to the museum.
Other research will investigate the source of Earth's liquid oceans and how minerals may have helped spark life, it said.
"This compositional shift likely marks the onset of modern-style plate tectonics and potentially could signal the emergence of life on Earth," Ackerson said.
"But we will need to do a lot more research to determine this geologic shift's connections to the origins of life," he said.