Clays in Antarctica from millions of years ago reveal past climate changes

Members of the TASMANDRAKE research group of the Andalusian Earth Sciences Institute (IACT), which pertains to the University of Granada and CSIC, have published a research paper in the prestigious international journal Scientific Reports describing their analysis of clays from Antarctica dating back 35.5 million years, to reconstruct past climate changes.

Glaucony grains observed under an electron microscope
[Credit: University of Granada]

Their study was conducted in the area known as Drake Passage—the body of water that separates South America from Antarctica, between Cape Horn (Chile) and the South Shetland Islands (Antarctica). The results help to better understand the climatic conditions prior to the formation of the Antarctic Circumpolar Current, thus evaluating possible links between the development of the ice sheet in Antarctica and the changes in the tectonic and paleoceanographic configuration. Such questions constitute key facets of past climate functioning that provide boundary conditions for today's climate models, which predict a general rise in sea levels over the coming centuries.

The article analyses the relevance as a climatic indicator of the mineral commonly known as 'glauconite', which is more properly termed 'the glauconia facies' or 'glauconia'. This is a type of green clay, formed mainly in shallow marine environments (<500 m) with temperatures below 15° C, under very specific oxygenation conditions.

The existence of this clay formation in the Antarctic region has received little scholarly attention to date compared to other geological records on the planet. The characteristic green-coloured mineral has been observed around Antarctica and the Antarctic Ocean in sedimentary sequences of the Terminal Eocene Event—that is, before one of the main climatic transitions in Earth's history. The Eocene–Oligocene climate transition took place approximately 34–33.6 million years ago.

Northwest region of the Antarctic Peninsula (South Shetland Islands)
[Credit: University of Granada]

This scientific contribution describes, for the first time in the Antarctic Ocean, a glauconitisation event (in which glauconia was formed) approximately 35.5 million years ago in the Weddell Sea, northeast of the Antarctic Peninsula between South America and Antarctica.

The formation of glauconia 35.5 million years ago marks the onset of progressive sea level rise in the north Weddell Sea during the Terminal Eocene. The results of this scientific study thus provide new insights regarding changes in paleoceanographic conditions just prior to the Eocene–Oligocene climate transition and the controversial opening and deepening of Drake Passage.

Studying the weather of the past to predict the future

The separation of the Antarctic continent from South America and Oceania allowed bodies of water to transfer freely between the Pacific and Atlantic Oceans. This new circulation of bodies of water resulted in the Circumpolar Current and, with it, the thermal insulation of the Antarctic and the formation of the ice cap on a continental scale.

Map of Antarctica showing the location of the Antarctic Circumpolar Current (ACC), which flows from west to east.
The ACC is a fundamental element in the deep global circulation connecting the Pacific, Atlantic, and Indian
Oceans. It is therefore an important part of the global ocean circulation network that distributes
 heat around the Earth [Credit: University of Granada]

The opening of Drake Passage between South America and the Antarctic Peninsula is therefore considered one of the most important events in the history of the Earth's oceanic and atmospheric circulation. However, in the absence of dating for the formation of the sedimentary basins of Drake Passage, it is difficult to specify the precise age when the Passage began to open up and the Circumpolar Current started to form. The glauconia analysis conducted by the TASMANDRAKE research group contributes to progress in this area of study.

To put these changes into perspective, Adrian Lopez Quiros, the principal author of the research, notes that "it is necessary to study the past to understand the present and help predict the future," by better understanding the tectonic, climatic, and paleoceanographic conditions that led to the onset and subsequent evolution of this important ocean current.

The United Nations' Intergovernmental Panel on Climate Change (IPCC), a major reference source for climate forecasts, established several possible future climate scenarios in 2014. However, the new data, when comparing simulations with real-world data, predict even greater impacts than those previously foreseen in the IPCC climate scenarios. Therefore, climate change is developing faster than previously thought. With its research, the TASMANDRAKE group aims to provide new variables for these models—focusing on sediments and geophysics—to ensure that its results reflect real-life events even more accurately, especially in terms of the transoceanic currents, global warming, and rising sea levels.

Source: University of Granada [January 23, 2020]

New research finds Earth's oldest asteroid strike linked to 'big thaw'

Curtin University scientists have discovered Earth's oldest asteroid strike occurred at Yarrabubba, in outback Western Australia, and coincided with the end of a global deep freeze known as a Snowball Earth.

The Yarrabubba Impact Structure
[Credit: Google Earth]

The research, published in the leading journal Nature Communications, used isotopic analysis of minerals to calculate the precise age of the Yarrabubba crater for the first time, putting it at 2.229 billion years old - making it 200 million years older than the next oldest impact.

Lead author Dr Timmons Erickson, from Curtin's School of Earth and Planetary Sciences and NASA's Johnson Space Center, together with a team including Professor Chris Kirkland, Associate Professor Nicholas Timms and Senior Research Fellow Dr Aaron Cavosie, all from Curtin's School of Earth and Planetary Sciences, analysed the minerals zircon and monazite that were 'shock recrystallized' by the asteroid strike, at the base of the eroded crater to determine the exact age of Yarrabubba.

The team inferred that the impact may have occurred into an ice-covered landscape, vaporised a large volume of ice into the atmosphere, and produced a 70km diameter crater in the rocks beneath.

Professor Kirkland said the timing raised the possibility that the Earth's oldest asteroid impact may have helped lift the planet out of a deep freeze.

"Yarrabubba, which sits between Sandstone and Meekatharra in central WA, had been recognised as an impact structure for many years, but its age wasn't well determined," Professor Kirkland said.

Researchers analysed 'shock crystallized' zircon to determine
the exact age of Yarrabubba [Credit: Curtin University]

"Now we know the Yarrabubba crater was made right at the end of what's commonly referred to as the early Snowball Earth - a time when the atmosphere and oceans were evolving and becoming more oxygenated and when rocks deposited on many continents recorded glacial conditions".

Associate Professor Nicholas Timms noted the precise coincidence between the Yarrabubba impact and the disappearance of glacial deposits.

"The age of the Yarrabubba impact matches the demise of a series of ancient glaciations. After the impact, glacial deposits are absent in the rock record for 400 million years. This twist of fate suggests that the large meteorite impact may have influenced global climate," Associate Professor Timms said.

"Numerical modelling further supports the connection between the effects of large impacts into ice and global climate change. Calculations indicated that an impact into an ice-covered continent could have sent half a trillion tons of water vapour - an important greenhouse gas - into the atmosphere. This finding raises the question whether this impact may have tipped the scales enough to end glacial conditions."

Dr Aaron Cavosie said the Yarrabubba study may have potentially significant implications for future impact crater discoveries.

"Our findings highlight that acquiring precise ages of known craters is important - this one sat in plain sight for nearly two decades before its significance was realised. Yarrabubba is about half the age of the Earth and it raises the question of whether all older impact craters have been eroded or if they are still out there waiting to be discovered," Dr Cavosie said.

Author: Lucien Wilkinson | Source: Curtin University [January 22, 2020]

Climate (not humans) shaped early forests of New England

A new study in the journal Nature Sustainability overturns long-held interpretations of the role humans played in shaping the American landscape before European colonization. The findings give new insight into the rationale and approaches for managing some of the most biodiverse landscapes in the eastern U.S.

Archaeologists Dianna Doucette, Deena Duranleau, and Randy Jardin conducting investigations at the Lucy Vincent Beach
 Site, Martha's Vineyard. The long-held belief that native people used fire to create a diverse landscape of woodlands,
grasslands, heathlands, and shrublands in New England has led to a widespread use of prescribed fire as a conservation
tool. Research by Oswald and colleagues indicates that these openlands actually arose following European contact,
deforestation, and agricultural expansion [Credit: Elizabeth Chilton, Binghamton University]

The study, led by archaeologists, ecologists, and paleoclimatologists at Harvard, Emerson College and elsewhere, focuses on the coast from Long Island to Cape Cod and the nearby islands of Nantucket, Martha's Vineyard, Block Island, and Naushon--areas that historically supported the greatest densities of Native people in New England and today are home to the highest concentrations of rare habitats in the region, including sandplain grasslands, heathlands, and pitch pine and scrub oak forests.

"For decades, there's been a growing popularization of the interpretation that, for millennia, Native people actively managed landscapes - clearing and burning forests, for example - to support horticulture, improve habitat for important plant and animal resources, and procure wood resources," says study co-author David Foster, Director of the Harvard Forest at Harvard University. This active management is said to have created an array of open-land habitats and enhanced regional biodiversity.

But, Foster says, the data reveal a new story. "Our data show a landscape that was dominated by intact, old-growth forests that were shaped largely by regional climate for thousands of years before European arrival."

Fires were uncommon, the study shows, and Native people foraged, hunted, and fished natural resources without actively clearing much land.

The long-held belief that native people used fire to create a diverse landscape of woodlands, grasslands,
heathlands, and shrublands in New England has led to a widespread use of prescribed fire as a
conservation tool. Research by Oswald and colleagues indicates that these openlands actually
 arose following European contact, deforestation, and agricultural expansion. These landscapes
and their critical habitats and species are best maintained through agricultural practices like
 grazing, as seen here on conservation land on the Elizabeth Islands, Massachusetts
[Credit: David Foster]

"Forest clearance and open grasslands and shrublands only appeared with widespread agriculture during the European colonial period, within the last few hundred years," says Wyatt Oswald, a professor at Emerson College and lead author of the study.

The authors say the findings transform thinking about how landscapes have been shaped in the past - and therefore how they should be managed in the future.

"Ancient Native people thrived under changing forest conditions not by intensively managing them but by adapting to them and the changing environment," notes Elizabeth Chilton, archaeologist, co-author of the study, and Dean of the Harpur College of Arts and Sciences at Binghamton University.

To reconstruct historical changes to the land, the research team combined archaeological records with more than two dozen intensive studies of vegetation, climate, and fire history spanning ten thousand years. They found that old-growth forests were predominant for millennia but are extremely uncommon today.

Conservationists have employed prescribed fire in an attempt to maintain openland habitats such
 as the Katama sandplain grassland on the island of Martha's Vineyard. Research by Oswald and
colleagues indicates that, despite a large human population for thousands of years, fire was
uncommon and landscapes across southern New England were heavily forested until
European contact and deforestation for agriculture. Grazing and other agricultural
practices can be used to maintain these uncommon habitats today
 [Credit: David Foster, Harvard University]

"Today, New England's species and habitat biodiversity are globally unique, and this research transforms our thinking and rationale for the best ways to maintain it," says Oswald. "It also points to the importance of historical research to help us interpret modern landscapes and conserve them effectively into the future."

The authors also note the unique role that colonial agriculture played in shaping landscapes and habitat. "European agriculture, especially the highly varied activity of sheep and cattle grazing, hay production, and orchard and vegetable cultivation in the 18th and 19th centuries, made it possible for open-land wildlife species and habitats that are now rare or endangered - such as the New England cottontail - to thrive," says Foster. Open-land species have declined dramatically as forests regrow on abandoned farmland, and housing and commercial development of both forests and farms have reduced their habitat.

Foster notes that the unique elements of biodiversity initiated through historical activities can be encouraged through analogous management practices today.

"Protected wildland reserves would preserve interior forest species that were abundant before European settlement," he says. "Lands managed through the diversified farming and forestry practices that created openlands and young forests during the colonial period would support another important suite of rare plants and animals."

The long-held belief that native people used fire to create a diverse landscape of woodlands, grasslands,
 heathlands, and shrublands in New England has led to a widespread use of prescribed fire as a
 conservation tool. Research by Oswald and colleagues indicates that these openlands actually
arose following European contact, deforestation, and agricultural expansion. These landscapes
 and their critical habitats and species are best maintained through agricultural practices like
grazing, as seen here on a hillside in Chilmark, Martha's Vineyard, MA.
[Credit: David Foster, Harvard University]

For successful conservation models that leverage this historical perspective, the authors point to efforts by The Trustees of Reservations, the oldest land trust in the world, which manages more than 25,000 acres in Massachusetts embracing old and young forests, farms, and many cultural resources. The organization uses livestock grazing to keep lands open for birds like bobolinks and meadowlarks, which in turn supports local farmers and produces food for local communities.

Jocelyn Forbush, Executive Vice President for the Trustees, says, "Maintaining the legacy of our conserved openlands in Massachusetts is an important goal for The Trustees and we are increasingly looking to agricultural practices to yield a range of outcomes. In particular, we are employing grazing practices to support the habitats of our open and early successional lands in addition to the scenic and cultural landscapes that shape the character of our communities."

Source: Harvard University [January 20, 2020]

New research provides evidence of strong early magnetic field around Earth

Deep within Earth, swirling liquid iron generates our planet's protective magnetic field. This magnetic field is invisible but is vital for life on Earth's surface: it shields the planet from harmful solar wind and cosmic rays from the sun.

Artist rendition of early Earth and Mars 4.2 billion years ago with internally generated magnetic fields. The long
life of the geodynamo and magnetic shielding prevented loss of the ocean on Earth, whereas the collapse of the
Martian magnetic field contributed to its loss of water [Credit: Michael Osadciw (University of Rochester,
Rochester, NY) & John A. Tarduno]

Given the importance of the magnetic field, scientists have been trying to figure out how the field has changed throughout Earth's history. That knowledge can provide clues to understanding the future evolution of Earth, as well as the evolution of other planets in the solar system.

New research from the University of Rochester provides evidence that the magnetic field that first formed around Earth was even stronger than scientists previously believed. The research, published in the Proceedings of the National Academy of Sciences, will help scientists draw conclusions about the sustainability of Earth's magnetic shield and whether or not there are other planets in the solar system with the conditions necessary to harbor life.

"This research is telling us something about the formation of a habitable planet," says John Tarduno, the William R. Kenan, Jr., Professor of Earth and Environmental Sciences and Dean of Research for Arts, Sciences, and Engineering at Rochester. "One of the questions we want to answer is why Earth evolved as it did and this gives us even more evidence that the magnetic shielding was recorded very early on the planet."

Earth's magnetic field today

Today's magnetic shield is generated in Earth's outer core. The intense heat in Earth's dense inner core causes the outer core—composed of liquid iron—to swirl and churn, generating electric currents, and driving a phenomenon called the geodynamo, which powers Earth's magnetic field. The currents in the liquid outer core are strongly affected by the heat that flows out of the solid inner core.

In order to determine the past magnetic field direction and intensity, the researchers dated and analyzed zircon crystals
collected from sites in Australia. The zircons are about two-tenths of a millimeter and contain even smaller magnetic
particles that lock in the magnetization of the earth at the time the zircons were formed. Here, a zircon crystal
is placed within the "O" on a dime, for scale [Credit: University of Rochester/John Tarduno]

Because of the location and extreme temperatures of materials in the core, scientists aren't able to directly measure the magnetic field. Fortunately, minerals that rise to Earth's surface contain tiny magnetic particles that lock in the direction and intensity of the magnetic field at the time the minerals cool from their molten state.

Using new paleomagnetic, electron microscope, geochemical, and paleointensity data, the researchers dated and analyzed zircon crystals—the oldest known terrestrial materials—collected from sites in Australia. The zircons, which are about two-tenths of a millimeter, contain even smaller magnetic particles that lock in the magnetization of the earth at the time the zircons were formed.

Earth's magnetic field 4 billion years ago

Previous research by Tarduno found that Earth's magnetic field is at least 4.2 billion years old and has existed for nearly as long as the planet. Earth's inner core, on the other hand, is a relatively recent addition: it formed only about 565 million years ago, according to research published by Tarduno and his colleagues earlier this year.

While the researchers initially believed Earth's early magnetic field had a weak intensity, the new zircon data suggests a stronger field. But, because the inner core had not yet formed, the strong field that originally developed 4 billion years ago must have been powered by a different mechanism.

"We think that mechanism is chemical precipitation of magnesium oxide within Earth," Tarduno says.

The magnesium oxide was likely dissolved by extreme heat related to the giant impact that formed Earth's moon. As the inside of Earth cooled, magnesium oxide could precipitate out, driving convection and the geodynamo. The researchers believe inner Earth eventually exhausted the magnesium oxide source to the point that the magnetic field almost completely collapsed 565 million years ago.

But the formation of the inner core provided a new source to power the geodynamo and the planetary magnetic shield Earth has today.

A magnetic field on Mars

"This early magnetic field was extremely important because it shielded the atmosphere and water removal from the early Earth when solar winds were most intense," Tarduno says. "The mechanism of field generation is almost certainly important for other bodies like other planets and exoplanets."

A leading theory, for instance, is that Mars, like Earth, had a magnetic field early on in its history. However, on Mars, the field collapsed and, unlike Earth, Mars did not generate a new one.

"Once Mars lost its magnetic shielding, it then lost its water," Tarduno says. "But we still don't know why the magnetic shielding collapsed. Early magnetic shielding is really important, but we're also interested in the sustainability of a magnetic field. This study gives us more data in trying to figure out the set of processes that maintain the magnetic shield on Earth."

Source: University of Rochester [January 20, 2020]

It was microbial mayhem in the Chicxulub crater, Curtin research suggests

New insights into how microbial life was quickly re-established following the mass extinction of the dinosaurs have been detailed for the first time by Curtin University-led research.

Impact illustration [Credit: Victor Leshyk]

The research, published in Geology, analyzed biomarkers, also known as molecular fossils, found in drill core rock samples from the center of the Chicxulub crater located in deep sea waters of the Gulf of Mexico.

The findings suggest that remains from land plants, fungi and coastal microbial mats, like modern stromatolites, were transported into the crater through wave activity during a giant tsunami in the immediate aftermath of the giant asteroid impact credited with causing the extinction of the dinosaurs, 66 million years ago.

Lead author Ph.D. candidate Bettina Schaefer, from the WA-Organic and Isotope Geochemistry Centre (WA-OIGC) in Curtin's School of Earth and Planetary Sciences, said the research study provided the first molecular evidence of many forms of photosynthetic life present in the Chicxulub crater, demonstrating how resilient microorganisms were after experiencing abnormally hostile conditions following the asteroid's impact.

"Our research shows that when the dust from the asteroid's impact settled and sunlight returned to ideal levels, there was a rapid resurgence of land plants, dinoflagellates, cyanobacteria and all forms of anaerobic photosynthetic sulfur bacteria, including those from microbial mats in the crater area," Ms Schaefer said.

John Curtin Distinguished Professor Kliti Grice, the founding director of WA-OIGC in Curtin's School of Earth and Planetary Sciences, said the research findings further suggested the phytoplankton communities in the post-impact crater basin continued to produce and evolve at a "rapid" rate.

"The development and productivity of phytoplankton was accompanied by major transitions in nutrient and oxygen supplies that shaped the recovery of microbial life. There was so much going on in such a short time frame, it really was like a post-apocalyptic microbial mayhem was happening in the Chicxulub crater."

Author: April Kleer | Source: Curtin University [January 20, 2020]