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Ancient Zircons Date of Ancient of Plate Tectonics to 3.6 Billion Years Ago – Event Key to Making Earth Hospitable to Life

Zircons studied by the research team, photographed with cathodoluminescence, a technique that allowed the team to visualize the inside of the crystals using a specialized scanning electron microscope. Dark circles on the zircons are the voids left by the laser used to analyze the age and chemistry of the zircons.

Scientists led by Michael Ackerson, a research geologist at Smithsonian’s National Museum of Natural History, provide new evidence that modern plate tectonics, a defining feature of Earth and its unique ability to support life, originated about 3.6 billion years ago.

The study, published May 14 in the journal Geochemical Perspective Letters, uses zircons, the oldest minerals ever found on Earth, to look back into the planet’s ancient past.

The team tested more than 3,500 zircons, each just a few human hairs wide, by bombarding them with a laser and then measuring their chemical composition with a mass spectrometer.

These tests revealed the age and underlying chemistry of each zircon. Of the thousands tested, about 200 were suitable for study due to the ravages of the billions of years these minerals have endured since their Zircons studied by the research team, photographed with cathodoluminescence, a technique that allowed the team to visualize the inside of the crystals using a specialized scanning electron microscope.

Dark circles on the zircons are the voids left by the laser used to analyze the age and chemistry of the zircons.

Scientists led by Michael Ackerson, a research geologist at Smithsonian’s National Museum of Natural History, provide new evidence that modern plate tectonics, a defining feature of Earth and its unique ability to support life, originated about 3.6 billion years ago.

The study, published May 14 in the journal Geochemical Perspective Letters, uses zircons, the oldest minerals ever found on Earth, to look back into the planet’s ancient past.

The team tested more than 3,500 zircons, each just a few human hairs wide, by bombarding them with a laser and then measuring their chemical composition with a mass spectrometer.

These tests revealed the age and underlying chemistry of each zircon. Of the thousands tested, about 200 were suitable for study due to the ravages of the billions of years these minerals have endured since their

The oldest minerals on Earth Date Beginning of plate tectonics to 3.6 billion years ago

Ancient zircons from the Jack Hills of Western Australia refine the date of an event critical to making the planet hospitable to life.

Scientists led by Michael Ackerson, a research geologist at Smithsonian’s National Museum of Natural History, provide new evidence that modern plate tectonics, a defining feature of Earth and its unique ability to support life, originated about 3.6 billion years ago.

Earth is the only planet known to harbor complex life, and that ability is based in part on another feature that makes the planet unique: plate tectonics.

No other planetary body known to science has a dynamic crustal split into continental plates that move, break, and collide for eons.

Plate tectonics connects the inner Earth’s chemical reactor to the surface that has created the habitable planet that humans enjoy today, from the oxygen in the atmosphere to the concentrations of climate-regulating carbon dioxide.

But when and how plate tectonics began has remained mysterious, buried under billions of years of geologic time.

The study, published May 14, 2021, in the journal Geochemical Perspectives Letters, uses zircons, the oldest minerals ever found on Earth, to look back into the planet’s ancient past.

The Jack Hills of Western Australia, where the zircons studied were sampled from 15 grapefruit-sized stones collected by the research team.

Scientists led by Michael Ackerson, a research geologist at Smithsonian’s National Museum of Natural History, provide new evidence that modern plate tectonics, a defining feature of Earth and its unique ability to support life, originated about 3.6 billion years ago.

The study, published May 14 in the journal Geochemical Perspective Letters, uses zircons, the oldest minerals ever found on Earth, to look back into the planet’s ancient past. Credit: Dustin Trail, University of Rochester

The oldest of the zircons in the study, which came from the Jack Hills of Western Australia, were about 4.3 billion years old – meaning these nearly indestructible minerals were formed when Earth itself was in its infancy, just about 200 million years old.

Along with other ancient zircons collected in the Jack Hills that span Earth’s earliest history up to 3 billion years ago, these minerals provide the closest researchers have to a continuous chemical record of the nascent world.

We are reconstructing how the Earth changed from a molten ball of stone and metal to what we have today, ”said Ackerson. “None of the other planets have continents or liquid oceans or life.

In a sense, we are trying to answer the question of why the Earth is unique, and we can, to some extent, answer that with these zircons.

To look billions of years into Earth’s past, Ackerson and the research team collected 15 grapefruit-sized rocks from the Jack Hills and reduced them to their smallest constituent parts – minerals – by grinding them into sand with a machine that called a chipmunk Fortunately zircons are very dense, making them relatively easy to separate from the rest of the sand using a technique similar to gold washing.

A thin, polished piece of rock collected in the Jack Hills of Western Australia. Using a special microscope equipped with a polarizing lens, the research team was able to examine the intricate quartz internal structure that makes up the rock, including unique features that allowed them to identify ancient zircons (magenta mineral in the center of the red outline inset image in the right photo).

Scientists led by Michael Ackerson, a research geologist at Smithsonian’s National Museum of Natural History, provide new evidence that modern plate tectonics, a defining feature of Earth and its unique ability to support life, originated about 3.6 billion years ago.

The study, published May 14 in the journal Geochemical Perspective Letters, uses zircons, the oldest minerals ever found on Earth, to look back into the planet’s ancient past.

To look billions of years into Earth’s past, Ackerson and the research team collected 15 grapefruit-sized rocks from the Jack Hills and reduced them to their smallest constituent parts – minerals – by grinding them to sand with a machine that made a called chipmunk.

Fortunately, zircons are very dense, making them relatively easy to separate from the rest of the sand using a technique similar to gold washing. Credit: Mi

The team tested more than 3,500 zircons, each just a few human hairs wide, by bombarding them with a laser and then measuring their chemical composition with a mass spectrometer.

These tests revealed the age and underlying chemistry of each zircon. Of the thousands tested, about 200 were suitable for study due to the ravages of the billions of years these minerals have endured since their creation.

“Unlocking the secrets contained in these minerals is not an easy task,” Ackerson said. “We’ve analyzed thousands of these crystals to come up with a handful of useful data points, but each sample has the potential to tell us something completely new and reshape how we understand the origins of our planet.

” The age of a zircon can be determined with a high degree of precision, because each zircon contains uranium. Uranium’s famously radioactive nature and well-quantified rate of decay allow scientists to reverse engineer how long the mineral has been around.

The aluminum content of each zircon was also of interest to the research team. Tests on modern zircons show that high aluminum content zircons can only be produced in a limited number of ways, allowing researchers to use the presence of aluminum to infer what was going on geologically at the time the zircon was formed.

After analyzing the results of the hundreds of usable zircons out of the thousands tested, Ackerson and his co-authors deciphered a marked increase in aluminum concentrations about 3.6 billion years ago.

“This compositional shift likely marks the beginning of modern plate tectonics and could potentially signal the origin of life on Earth,” Ackerson said. “But we will need to do a lot more research to establish the link between this geological shift and the origin of life.

” The line of inference connecting high-aluminum zircons to the beginning of a dynamic plate tectonics crust goes like this: One of the few ways high-aluminum zircons are formed is by melting rocks deeper below the Earth’s surface.

“It’s very difficult to get aluminum into zircons because of their chemical bonds,” Ackerson said. “You need some pretty extreme geological conditions.

” Ackerson reasons that this sign that rocks were melting deeper below the Earth’s surface meant that the Earth’s crust was thickening and starting to cool, and that this crustal thickening was a sign that the transition to modern plate tectonics was underway.

Previous research on the 4-billion-year-old Acasta Gneiss in northern Canada also suggests that the Earth’s crust thickened and caused rocks to melt deeper in the planet.

“The results of the Acasta Gneiss give us more confidence in our interpretation of the Jack Hills zircons,” Ackerson said.

“Today these locations are thousands of miles apart, but they tell us a fairly consistent story, which is that about 3.6 billion years ago something important happened worldwide.”

This work is part of the museum’s new initiative called Our Unique Planet, a public-private partnership that supports research into some of the most enduring and important questions about what makes Earth special.

Other research will explore the source of Earth’s liquid oceans and how minerals may have contributed to the creation of life.

Ackerson said he hopes to follow up on these results by searching the ancient Jack Hills zircons for traces of life and by looking at other extremely ancient rock formations to see if they too show signs of crustal thickening, about 3.6 billion years ago. Reference:

“Rise of peraluminous crustal magmas and implications for the early Earth” by M.R. Ackerson, D. Trail and J. Buettner, May 14, 2021, Geochemical Perspectives Letters.