̽��ֱ�� of Cambridge - Carleton ̽��ֱ��

Traces of Earth’s early magma ocean identified in Greenland rocks

cmm201 — Fri, 12 Mar 2021 19:00:00 +0000

̽��ֱ��study, published in the journal Science Advances, yields information on an important period in our planet’s formation, when a deep sea of incandescent magma stretched across Earth’s surface and extended hundreds of kilometres into its interior.

It is the gradual cooling and crystallisation of this ‘magma ocean’ that set the chemistry of Earth’s interior – a defining stage in the assembly of our planet’s structure and the formation of our early atmosphere.

Scientists know that catastrophic impacts during the formation of the Earth and Moon would have generated enough energy to melt our planet's interior. But we don’t know much about this distant and fiery phase of Earth’s history because tectonic processes have recycled almost all rocks older than 4 billion years.

Now researchers have found the chemical remnants of the magma ocean in 3.6-billion-year-old rocks from southwestern Greenland.

̽��ֱ��findings support the long-held theory that Earth was once almost entirely molten and provide a window into a time when the planet started to solidify and develop the chemistry that now governs its internal structure. ̽��ֱ��research suggests that other rocks on Earth’s surface may also preserve evidence of ancient magma oceans.

“There are few opportunities to get geological constraints on the events in the first billion years of Earth’s history. 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,” said lead author Dr Helen Williams, from Cambridge’s Department of Earth Sciences.

̽��ֱ��study brings forensic chemical analysis together with thermodynamic modelling in search of the primeval origins of the Greenland rocks, and how they got to the surface.

At first glance, the rocks that makeup Greenland’s Isua supracrustal belt look just like any modern basalt you’d find on the seafloor. But this outcrop, which was first described in the 1960s, is the oldest exposure of rocks on Earth. It is known to contain the earliest evidence of microbial life and plate tectonics.

̽��ֱ��new research shows that the Isua rocks also preserve rare evidence which even predates plate tectonics – the residues of some of the crystals left behind as that magma ocean cooled.

“It was a combination of some new chemical analyses we did and the previously published data that flagged to us that the Isua rocks might contain traces of ancient material. ̽��ֱ��hafnium and neodymium isotopes were really tantalizing, because those isotope systems are very hard to modify – so we had to look at their chemistry in more detail,” said co-author Dr Hanika Rizo, from Carleton ̽��ֱ��.

Iron isotopic systematics confirmed to Williams and the team that the Isua rocks were derived from parts of the Earth’s interior that formed as a consequence of magma ocean crystallisation.

Most of this primeval rock has been mixed up by convection in the mantle, but scientists think that some isolated zones deep at the mantle-core boundary – ancient crystal graveyards – may have remained undisturbed for billions of years.

It’s the relics of these crystal graveyards that Williams and her colleagues observed in the Isua rock chemistry. “Those samples with the iron fingerprint also have a tungsten anomaly – a signature of Earth’s formation – which makes us think that their origin can be traced back to these primeval crystals,” said Williams.

But how did these signals from the deep mantle find their way up to the surface? Their isotopic makeup shows they were not just funnelled up from melting at the core-mantle boundary. Their journey was more circuitous, involving several stages of crystallization and remelting – a kind of distillation process. ̽��ֱ��mix of ancient crystals and magma would have first migrated to the upper mantle, where it was churned up to create a ‘marble cake’ of rocks from different depths. Later melting of that hybrid of rocks is what produced the magma which fed this part of Greenland.

̽��ֱ��team’s findings suggest that modern hotspot volcanoes, which are thought to have formed relatively recently, may actually be influenced by ancient processes. “ ̽��ֱ��geochemical signals we report in the Greenland rocks bear similarities to rocks erupted from hotspot volcanoes like Hawaii – something we are interested in is whether they might also be tapping into the depths and accessing regions of the interior usually beyond our reach,” said Dr Oliver Shorttle who is jointly based at Cambridge’s Department of Earth Sciences and Institute of Astronomy.

̽��ֱ��team’s findings came out of a project funded by Deep Volatiles, a NERC-funded 5-year research programme. They now plan to continue their quest to understand the magma ocean by widening their search for clues in ancient rocks and experimentally modelling isotopic fractionation in the lower mantle.

“We’ve been able to unpick what one part of our planet’s interior was doing billions of years ago, but to fill in the picture further we must keep searching for more chemical clues in ancient rocks,” said co-author Dr Simon Matthews from the ̽��ֱ�� of Iceland.

Scientists have often been reluctant to look for chemical evidence of these ancient events. “ ̽��ֱ��evidence is often altered by the course of time. 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,” said Williams.

Reference:
Helen M. Williams et al. ‘Iron isotopes trace primordial magma ocean cumulates melting in Earth’s upper mantle.’ Science Advances (2021). DOI: 10.1126/sciadv.abc7394

New research led by the ̽��ֱ�� of Cambridge has found rare evidence – preserved in the chemistry of ancient rocks from Greenland - which tells of a time when Earth was almost entirely molten.

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

Helen Williams

Hanika Rizo

Isua in Greenland

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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First atlas of Inuit Arctic trails launched

fpjl2 — Tue, 10 Jun 2014 10:39:48 +0000

For centuries, indigenous peoples in the Arctic navigated the land, sea, and ice, using knowledge of trails that was passed down through the generations.

Now, researchers have mapped these ancient routes using archival and published accounts of encounters with Inuit stretching back through the 19th and 20th centuries, and have released it online for the public as an interactive atlas – bringing together hundreds of years of accrued cultural knowledge for the first time.

̽��ֱ��atlas, found at paninuittrails.org, is constructed from historical records, maps, trails and place names, and allows the first overview of the "pan-Inuit" world that is being fragmented as the annual sea ice diminishes and commercial mining and oil drilling encroaches.

Researchers say the atlas is important not just for cultural preservation but to show the geographical extent and connectedness of Inuit occupancy – illustrating their historic sovereignty and mobility over a resource-rich area with important trade routes that are opening up due to climate change.

"To the untutored eye, these trails may seem arbitrary and indistinguishable from surrounding landscapes. But for Inuit, the subtle features and contours are etched into their narratives and story-telling traditions with extraordinary precision," said Dr Michael Bravo from Cambridge ̽��ֱ��'s Scott Polar Research Institute, who co-directed the research with colleagues Claudio Aporta from Dalhousie ̽��ֱ��, and Fraser Taylor from Carleton ̽��ֱ�� in Canada.

"This atlas is a first step in making visible some of the most important tracks and trails spanning the North American continent from one end to the other."

Over the course of centuries, Arctic peoples established a network of trails – routes across the sea ice in the winter, and across open water in the summer, that stretched for hundreds of kilometres, allowing them to follow the seasonal movements of sea and land mammals on which their lives depended.

̽��ֱ��intricate network of trails also connected Inuit groups with each other. ̽��ֱ��atlas shows that, when brought together, these connections span the continent from Greenland to Alaska. Understanding the trails is essential to appreciating Inuit history and occupancy of the Arctic, say the researchers, for which the new atlas is a vital step.

"Essentially the trails and the atlas reduce the topology of the Arctic, revealing it to be a smaller, richer, and more intimate world," Bravo said. "For all that the 19th century explorers had military equipment and scientific instruments, they lacked the very precise indigenous knowledge about the routes, patterns, and timing of animal movements. That mattered in a place where the margins of survival could be extremely narrow."

̽��ֱ��documents that form the foundation of the new atlas consist of accounts – both published and unpublished – of encounters with Inuit by explorers, scientists, ethnographers and other visitors seeking access to the traditional indigenous knowledge to unlock the geographical secrets of the Arctic.

̽��ֱ��material has been digitised and organised geo-spatially, with trails mapped out over satellite imagery using global positioning systems. It constitutes the first attempt to map the ancient hubs and networks that have long-existed in a part of the world frequently and wrongly depicted as 'empty': as though an unclaimed stretch of vacant space.

This notion of emptiness is one that benefits those governments and corporations whose investments in shipping routes into the northern archipelago conveniently downplay the presence of the people that have lived there for centuries.

̽��ֱ��atlas provides evidence of the use and occupancy patterns of coastal and marine areas that intersect and overlap with significant parts of the Northwest Passage – the focus of recent mineral exploration and potentially a major shipping route. Historical printed sources like those found in the atlas are important for understanding the spatial extent of Inuit sovereignty, say the team, as these records reflect well-established Inuit networks.

In fact, because the maps are the product of encounters between Inuit and outsiders, the new resource also shows patterns of non-Inuit exploration – Western desires and ambitions to map and, at times, possess the Arctic.

"Most of the Inuit trails and place names recorded by explorers and other Arctic visitors are still used by Inuit today. They passed this knowledge on for hundreds of years, indicating intensive and extensive use of land and marine areas across the North American Arctic," said co-director Claudio Aporta.

While much of the Arctic appears 'featureless' to outsiders, it's not – and the Inuit learned how to read the fine-grained details of this landscape. Knowledge of the trails was attained by remembering specific journeys they themselves had taken, or learning in detail instructions in the oral narratives passed on by others.

̽��ֱ��Inuit were able to read the snow, the prevailing wind, the thickness of the ice, and the landscape as a whole. Over hundreds of years, their culture and way of life was, therefore, written into the landscape. ̽��ֱ��region became an intimate part of who they are.

" ̽��ֱ��trails are lived, remembered, and celebrated through the connections that ultimately reflect the Inuit traditions of sharing life while travelling," said Bravo.

" ̽��ֱ��geographical range of the atlas is a testimony to the legacy of the Inuit people, their remarkable collective memory built on practices of detailed observation, and motivated by an enduring sense of curiosity, as well as a set of ethical obligations to the living world they inhabit," he said.

Inset images: Inuit trails and Dr Michael Bravo in the Arctic

New digital resource brings together centuries of cultural knowledge for the first time, showing that networks of trails over snow and sea ice, seemingly unconnected to the untrained eye, in fact span a continent – and that the Inuit have long-occupied one of the most resource-rich and contested areas on the planet.

̽��ֱ��trails are lived, remembered, and celebrated through the connections that ultimately reflect the Inuit traditions of sharing life while travelling

Michael Bravo

Claudio Aporta

Example of an Inuit Arctic trail

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