From University of Chicago(US) and Carleton University(CA) via Science Alert(AU): “Ancient Magma From Earth’s Early Days Discovered in Rocks From Greenland”

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From University of Chicago(US)

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ScienceAlert

Science Alert(AU)

12 MARCH 2021
MIKE MCRAE

1
Isua Greenland Belt. Credit: Hanika Rizo.

Our planet’s surface has seen a thing or two in its 4.5 billion-odd-years of existence. Weathered by ocean, corroded by wind, and remolded by the relentless turnover of plate tectonics, we might assume nothing remains of Earth in its most primitive state.

Yet an analysis of rocks from a formation in Greenland reveals traces of a geological journey that took place at a time when our rocky world was little more than a molten ocean of magma, and it could fill in missing details on our ancient past.

Researchers from the University of Cambridge(UK) and Carleton University(CA) paid particular attention to signature levels of iron isotopes in a powdered sample of basalt taken from the northern parts of the Isua Greenland Belt (ISB).

Along with a study of its tungsten, the chemical signatures reflect the basalt’s birth from a mix of components from different parts of the mantle at a time when Earth’s entirely molten surface was hardening.

The Isua belt is a strip of crust in Greenland’s southwest that has remained relatively unchanged for a mind-blowing 3.7 billion years, officially making them the oldest rocks on Earth.

For more than half a century the ISB has been a regular haunt for planetary scientists and biologists keen to learn more about how our planet’s crust formed, and how its chemistry – including the earliest forms of life – might have emerged.

As old as the belt might be, Earth had already been a planet of sorts for a good half a billion years prior to their formation. Not that we’d recognize it now.

Heated by frequent collisions of new material raining down from space and radioactive materials that hadn’t yet sunk to the planet’s core, there was no crust yet as such – just a churning blob of mineral soup.

We can work that much out by applying models of planetary formation, but many of the finer details of what went on below remain sketchy. What kinds of currents were rising and falling in our planet’s guts? How was energy transferred? What sorts of minerals might have crystallized out of solution as it cooled?

These are questions that could be answered if we had pristine samples of that magma. Fortunately, that’s just what happens to be locked up in Isua.

“There are few opportunities to get geological constraints on the events in the first billion years of Earth’s history,” says lead study author, Earth scientist Helen Williams from the University of Cambridge.

“It’s astonishing that we can even hold these rocks in our hands – let alone get so much detail about the early history of our planet.”

Previous research [Earth and Planetary Science Letters] on the sample’s recipe of hafnium and neodymium isotopes had already hinted at the rock’s origins spewing out of the planet’s mantle some 3.7 billion years ago, potentially preserving signatures of a time when the magma ocean was still crystallizing.

Measuring a specific isotope of iron in the rock’s make-up cemented speculations that at least some of it had been flowing as a liquid just beneath ancient Earth’s first skin.

Other measurements suggested there was more to the story, though, revealing a component made up of minerals that had risen from much deeper down.

That deeper rock shows signs of spending time in the lower mantle, with evidence of being forged by dynamic processes that involved a cycle of melting and crystallization before being blended with material in the upper mantle.

Fresh new volcanic rocks blasted onto the surface in other parts of the world today display similar signs of mixing, suggesting it’s possible ancient processes close to the planet’s core are still at work deep beneath our feet today.

Tying together the evidence to show exactly how our adolescent Earth chilled out and crusted up will take a lot more evidence.

Ancient records of Earth’s distant past will continue to erode away slowly. Fortunately we’re quickly learning how to unravel the clues they contain.

“The evidence is often altered by the course of time,” says Williams.

“But the fact we found what we did suggests that the chemistry of other ancient rocks may yield further insights into the Earth’s formation and evolution – and that’s immensely exciting.”

This research was published in Science Advances.

See the full article here .

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The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with UChicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

UChicago research has led to such breakthroughs as discovering the link between cancer and genetics; establishing revolutionary theories of economics; and developing tools to produce reliably excellent urban schooling. We generate new insights for the benefit of present and future generations.

The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts.