Scientists Discover Earth’s Youngest Banded Iron Formation In Western China

The banded iron formation, located in western China, has been conclusively dated as Cambrian in age. Approximately 527 million years old, this formation is young by comparison to the majority of discoveries to date. The deposition of banded iron formations, which began approximately 3.8 billion years ago, had long been thought to terminate before the beginning of the Cambrian Period at 540 million years ago.

“This is critical, as it is the first observation of a Precambrian-like banded iron formation that is Early Cambrian in age. This offers the most conclusive evidence for the presence of widespread iron-rich conditions at a time, confirming what has recently been suggested from geochemical proxies,” said Kurt Konhauser, professor in the Department of Earth and Atmospheric Sciences and co-author. Konhauser supervised the research that was led by Zhiquan Li, a PhD candidate from Beijing while on exchange at UAlberta.

The Early Cambrian is known for the rise of animals, so the level of oxygen in seawater should have been closer to near modern levels. “This is important as the availability of oxygen has long been thought to be a handbrake on the evolution of complex life, and one that should have been alleviated by the Early Cambrian,” says Leslie Robbins, a PhD candidate in Konhauser’s lab and a co-author on the paper.

The researchers compared the geological characteristics and geochemistry to ancient and modern samples to find an analogue for their deposition. The team relied on the use of rare earth element patterns to demonstrate that the deposit formed in, or near, a chemocline in a stratified iron-rich basin.

“Future studies will aim to quantify the full extent of these Cambrian banded iron formations in China and whether similar deposits can be found elsewhere,” says Kurt Konhauser.

Oxygen Levels On Early Earth Rose, Fell Several Times Before Great Oxidation Event

Earth’s oxygen levels rose and fell more than once hundreds of millions of years before the planetwide success of the Great Oxidation Event about 2.4 billion years ago, new research from the University of Washington shows.

The evidence comes from a new study that indicates a second and much earlier “whiff” of oxygen in Earth’s distant past — in the atmosphere and on the surface of a large stretch of ocean — showing that the oxygenation of the Earth was a complex process of repeated trying and failing over a vast stretch of time.

The finding also may have implications in the search for life beyond Earth. Coming years will bring powerful new ground- and space-based telescopes able to analyze the atmospheres of distant planets. This work could help keep astronomers from unduly ruling out “false negatives,” or inhabited planets that may not at first appear to be so due to undetectable oxygen levels.

“The production and destruction of oxygen in the ocean and atmosphere over time was a war with no evidence of a clear winner, until the Great Oxidation Event,” said Matt Koehler, a UW doctoral student in Earth and space sciences and lead author of a new paper published the week of July 9 in the Proceedings of the National Academy of Sciences.

“These transient oxygenation events were battles in the war, when the balance tipped more in favor of oxygenation.”

In 2007, co-author Roger Buick, UW professor of Earth and space sciences, was part of an international team of scientists that found evidence of an episode — a “whiff” — of oxygen some 50 million to 100 million years before the Great Oxidation Event. This they learned by drilling deep into sedimentary rock of the Mount McRae Shale in Western Australia and analyzing the samples for the trace metals molybdenum and rhenium, accumulation of which is dependent on oxygen in the environment.

Now, a team led by Koehler has confirmed a second such appearance of oxygen in Earth’s past, this time roughly 150 million years earlier — or about 2.66 billion years ago — and lasting for less than 50 million years. For this work they used two different proxies for oxygen — nitrogen isotopes and the element selenium — substances that, each in its way, also tell of the presence of oxygen.

“What we have in this paper is another detection, at high resolution, of a transient whiff of oxygen,” said Koehler. “Nitrogen isotopes tell a story about oxygenation of the surface ocean, and this oxygenation spans hundreds of kilometers across a marine basin and lasts for somewhere less than 50 million years.”

The team analyzed drill samples taken by Buick in 2012 at another site in the northwestern part of Western Australia called the Jeerinah Formation.

The researchers drilled two cores about 300 kilometers apart but through the same sedimentary rocks — one core samples sediments deposited in shallower waters, and the other samples sediments from deeper waters. Analyzing successive layers in the rocks years shows, Buick said, a “stepwise” change in nitrogen isotopes “and then back again to zero. This can only be interpreted as meaning that there is oxygen in the environment. It’s really cool — and it’s sudden.”

The nitrogen isotopes reveal the activity of certain marine microorganisms that use oxygen to form nitrate, and other microorganisms that use this nitrate for energy. The data collected from nitrogen isotopes sample the surface of the ocean, while selenium suggests oxygen in the air of ancient Earth. Koehler said the deep ocean was likely anoxic, or without oxygen, at the time.

The team found plentiful selenium in the shallow hole only, meaning that it came from the nearby land, not making it to deeper water. Selenium is held in sulfur minerals on land; higher atmospheric oxygen would cause more selenium to be leached from the land through oxidative weathering — “the rusting of rocks,” Buick said — and transported to sea.

“That selenium then accumulates in ocean sediments,” Koehler said. “So when we measure a spike in selenium abundances in ocean sediments, it could mean there was a temporary increase in atmospheric oxygen.”

The finding, Buick and Koehler said, also has relevance for detecting life on exoplanets, or those beyond the solar system.

“One of the strongest atmospheric biosignatures is thought to be oxygen, but this study confirms that during a planet’s transition to becoming permanently oxygenated, its surface environments may be oxic for intervals of only a few million years and then slip back into anoxia,” Buick said.

“So, if you fail to detect oxygen in a planet’s atmosphere, that doesn’t mean that the planet is uninhabited or even that it lacks photosynthetic life. Merely that it hasn’t built up enough sources of oxygen to overwhelm the ‘sinks’ for any longer than a short interval.

“In other words, lack of oxygen can easily be a ‘false negative’ for life.”

Koehler added: “You could be looking at a planet and not see any oxygen — but it could be teeming with microbial life.”

Stability Of Earth: Scientists Propose Solution To ‘Gaia Puzzle’

Scientists may have solved a long-standing puzzle over why conditions on Earth have remained stable enough for life to evolve over billions of years. The ‘Gaia’ hypothesis proposed that living things interacting with inorganic processes somehow keep the planet in a state where life can persist — despite threats such as a brightening sun, volcanoes and meteorite strikes.

The puzzle of how this might work has divided experts for decades, but a team led by scientists from the University of Exeter have proposed a solution. They say stability could come from “sequential selection” in which situations where life destabilises the environment tend to be short-lived and result in further change until a stable situation emerges, which then tends to persist.

Once this happens, the system has more time to acquire further traits that help to stabilise and maintain it — a process known as “selection by survival alone.”

“We can now explain how the Earth has accumulated stabilising mechanisms over the past 3.5 billion years of life on the planet,” said Professor Tim Lenton, of the University of Exeter.

“The central problem with the original Gaia hypothesis was that evolution via natural selection cannot explain how the whole planet came to have stabilising properties over geologic timescales.”

“Instead, we show that at least two simpler mechanisms work together to give our planet with life self-stabilising properties.”

He added: “Our findings can help explain how we came to be here to wonder about this question in the first place.”

Professor Dave Wilkinson, of the University of Lincoln, who was also involved in the research, added: “I have been involved in trying to figure out how

Gaia might work for over 20 years — finally it looks like a series of promising ideas are all coming together to provide the understanding I have been searching for.”

Dr James Dyke, of the University of Southampton, also an author on the paper, said: “As well as being important for helping to estimate the probability of complex life elsewhere in the universe, the mechanisms we identify may prove crucial in understanding how our home planet may respond to drivers such as human-produced climate change and extinction events.”

Creating transformative solutions to the global changes that humans are now causing is a key focus of the University of Exeter’s new Global Systems Institute, directed by Professor Lenton, who said: “We can learn some lessons from Gaia on how to create a flourishing, sustainable, stable future for 9-11 billion people this century.”

The Gaia hypothesis, first put forward by James Lovelock in the 1970s, was named after the deity who personified the Earth in Greek mythology.

Seismologists Use Massive Earthquakes To Unlock Secrets Of The Outer Core

By applying new data and Princeton’s supercomputers to the classic question of what lies beneath our feet, Princeton seismologist Jessica Irving and an international team of colleagues have developed a new model for the Earth’s outer core, a liquid iron region deep in the Earth.

The outer core is churning constantly, sustaining the planet’s magnetic field and providing heat to the mantle. “Understanding the outer core is crucial for understanding the history of the magnetic field,” said Irving, an assistant professor of geosciences. Her team’s work appears today in the journal Science Advances.

“The model we have produced, EPOC—Elastic Parameters of the Outer Core—is going to be the background model, the one thing that underlies everything else,” said Irving. The researchers describe EPOC as an outer core update of the existing Preliminary Earth Reference Model (PREM), a model of how fundamental Earth properties vary with depth, which was developed almost 40 years ago.

The key data in the research came from “normal modes,” which are standing waves that can be measured after the very largest earthquakes, typically magnitude 7.5 or higher. Unlike the body waves and surface waves that most seismologists study, normal modes are “the vibration of the whole Earth at once, which is kind of an amazing thing to think about,” Irving said. “We could say that the Earth ‘rings like a bell,’ at characteristic frequencies.”

The new model, EPOC, was first envisioned at a four-week summer science workshop where Irving was housed with fellow seismologists Sanne Cottaar, at the University of Cambridge, and Vedran Leki?, at the University of Maryland-College Park.

“PREM is a venerable, very simple, well-regarded model, but it can’t represent any small-scale structures,” Irving said. “We thought, ‘Can we make a simple model, with even fewer parameters than PREM, that does the job just as well?’ It turned out we could make a model that does the job much better.”

For one, EPOC reduces the need for a “complicated little layer” at the boundary between the core and the mantle, she said. Researchers in recent decades had found discrepancies between the PREM-predicted body wave velocity and the data they were finding, especially at the top of the core, and some had argued that there must be an anomalously slow layer hidden there. They debated how thick it should be—estimates range from 50 to 300 miles—and exactly what it must be composed of.

Her team’s model doesn’t offer any more specifics than PREM, Irving said, “but we suggest that because EPOC fits the data better, maybe you don’t need this little layer.” And additionally, it provides information about the material properties of the outer core.

The outer core is vitally important to the thermal history of the planet and its magnetic field, said Irving, but “it’s not tangible. We can’t show you a rock from the outer core. But at the same time, it is such a huge section of our planet. The core has roughly 30 percent of the mass of the planet in it. The crust is insignificant by comparison. There is so much that we don’t understand about the deep earth—and these aren’t even the complicated properties. We’re just looking for the very slowly varying bulk properties.”

To create their model, Irving and fellow seismologists pooled their skills. Cottaar had experience with equations of state—the physics explaining the connections between temperature, pressure, volume and other fundamental characteristics—and Leki? was fluent in Bayesian techniques, a probabilistic approach that helped the team sift through countless possible models and find the most likely ones. And because of her background with normal mode seismology, Irving knew how to work with the newly updated dataset.

“So all three of us were seismologists with different specialized skill sets, and we liked to have coffee at breakfast together,” Irving said. “It’s so much fun doing science with friends.”

The researchers fed the equations of state into Princeton’s Tiger supercomputer cluster to generate millions of possible models of the outer core. “Every six seconds we created a new model,” Irving said. “Some we rejected because they looked wrong. We have scientific tests for ‘wrong,’ for models that say things like, ‘The mass of the Earth should be twice what we think it is.'”

The team then took the best of the models and used them to predict what frequencies the whole Earth would shake at after a massive earthquake. The researchers compared the measured frequencies of normal modes to the predictions from their models until they found their preferred model.

When teaching about normal modes, Irving uses the metaphor of two bells, one of brass and one of steel, both painted white. “If you hit those bells, you’ll get different notes out of them, and that will tell you that you have different materials in there,” she said. “The exact frequencies—the exact pitch that the Earth at shakes after these very large earthquakes—depends on the material properties of the Earth. Just like we can’t see through the paint on the bells, we can’t see through the planet, but we can listen for the pitch, the frequencies of these whole-Earth observations, and use them to make inferences about what’s going on deep in the Earth.”

Yosemite Granite ‘Tells A Different Story’ About Earth’s Geologic History

A team of scientists including Carnegie’s Michael Ackerson and Bjorn Mysen revealed that granites from Yosemite National Park contain minerals that crystallized at much lower temperatures than previously thought possible. This finding upends scientific understanding of how granites form and what they can teach us about our planet’s geologic history. Their work is published in Nature.

Granites are igneous rocks comprised predominately of the minerals quartz and feldspar. They are the link between igneous processes that occur within the Earth and volcanic rocks that solidified on Earth’s surface.

“Granites are the ultimate product of the processes by which our planet separated into layers and they are key to understanding the formation of the continental crust,” Ackerson said. “Minerals from granites record almost all of our planet’s history — from 4.4 billion years ago to today.”

So, understanding the conditions under which granites form is important to geoscientists trying to unravel the processes that have shaped the Earth.

Until now, the prevailing wisdom on granites was that the minerals that comprise them crystallize as the molten rock cools to temperatures between 650 and 700 degrees Celsius (or between about 1,200 and 1,300 degrees Fahrenheit). Below these temperatures, the granites have been assumed to be completely crystallized.

It was previously known that under certain conditions some of the minerals of which granite is comprised can solidify at lower temperatures. So, the team — which also included Nicholas Tailby of the American Museum of Natural History and Bruce Watson of the Rensselaer Polytechnic Institute — used lab analysis to determine the temperatures of granite crystallization in granites from Yosemite National Park.

The team employed a technique called titanium in quartz thermometry. By measuring the amount of titanium dissolved in the quartz crystals, the team was able to determine the temperatures at which it crystallized deep in the Earth when the granites formed 90 million years ago.

They demonstrated that quartz crystals in samples of a body of granite body called the Tuolumne Intrusive Suite in Yosemite crystallized at temperatures between 474 and 561 Celsius (or 885 and 1,042 degrees Fahrenheit) — up to 200 degrees cooler than previously thought possible for granites.

“These granites tell a different story,” Ackerson added. “And it could rewrite what we think we understand about how Earth’s continents form.”

These findings could influence our understanding of the conditions in which the Earth’s crust first formed during the Hadean and Archean. They could also explain some recent observations about the temperature at which volcanic magmas exist before eruption and the mechanisms through which economically important ore deposits form.

Researchers Discover Volcanic Heat as Source Under Antarctic Glacier

A researcher from the University of Rhode Island’s Graduate School of Oceanography and five other scientists have discovered an active volcanic heat source beneath the Pine Island Glacier in Antarctica.

The discovery and other findings, which are critical to understanding the stability of the West Antarctic Ice Sheet, of which the Pine Island Glacier is a part, are published in the paper, “Evidence of an active volcanic heat source beneath the Pine Island Glacier,” in the latest edition of Nature Communications.

Assistant Professor Brice Loose of Newport, a chemical oceanographer at GSO and the lead author, said the paper is based on research conducted during a major expedition in 2014 to Antarctica led by scientists from the United Kingdom. They worked aboard an icebreaker, the RRS James Clark Ross, from January to March, Antarctica’s summer.

“We were looking to better understand the role of the ocean in melting the ice shelf,” Loose said. “I was sampling the water for five different noble gases, including helium and xenon. I use these noble gases to trace ice melt as well as heat transport. Helium-3, the gas that indicates volcanism, is one of the suite of gases that we obtain from this tracing method.

“We weren’t looking for volcanism, we were using these gases to trace other actions,” he said. “When we first started seeing high concentrations of helium-3, we thought we had a cluster of bad or suspicious data.”

The West Antarctic Ice Sheet lies atop a major volcanic rift system, but there had been no evidence of current magmatic activity, the URI scientist said. The last such activity was 2,200 years ago, Loose said. And while volcanic heat can be traced to dormant volcanoes, what the scientists found at Pine Island was new.

NASA Study Solves Glacier Puzzle

A new NASA study explains why the Tracy and Heilprin glaciers, which flow side by side into Inglefield Gulf in northwest Greenland, are melting at radically different rates.

Using ocean data from NASA’s Oceans Melting Greenland (OMG) campaign, the study documents a plume of warm water flowing up Tracy’s underwater face, and a much colder plume in front of Heilprin. Scientists have assumed plumes like these exist for glaciers all around Greenland, but this is the first time their effects have been measured.

The finding highlights the critical role of oceans in glacial ice loss and their importance for understanding future sea level rise. A paper on the research was published June 21 in the journal Oceanography.

Tracy and Heilprin were first observed by explorers in 1892 and have been measured sporadically ever since. Even though the adjoining glaciers experience the same weather and ocean conditions, Heilprin has retreated upstream less than 2.5 miles (4 kilometers) in 125 years, while Tracy has retreated more than 9.5 miles (15 kilometers). That means Tracy is losing ice almost four times faster than its next-door neighbor.

This is the kind of puzzle OMG was designed to explain. The five-year campaign is quantifying ice loss from all glaciers that drain the Greenland Ice Sheet with an airborne survey of ocean and ice conditions around the entire coastline, collecting data through 2020. OMG is making additional boat-based measurements in areas where the seafloor topography and depths are inadequately known.

About a decade ago, NASA’s Operation IceBridge used ice-penetrating radar to document a major difference between the glaciers: Tracy is seated on bedrock at a depth of about 2,000 feet (610 meters) below the ocean surface, while Heilprin extends only 1,100 feet (350 meters) beneath the waves.

Scientists would expect this difference to affect the melt rates, because the top ocean layer around Greenland is colder than the deep water, which has traveled north from the midlatitudes in ocean currents. The warm water layer starts about 660 feet (200 meters) down from the surface, and the deeper the water, the warmer it is. Naturally, a deeper glacier would be exposed to more of this warm water than a shallower glacier would.

When OMG Principal Investigator Josh Willis of NASA’s Jet Propulsion Laboratory in Pasadena, California, looked for more data to quantify the difference between Tracy and Heilprin, “I couldn’t find any previous observations of ocean temperature and salinity in the fjord at all,” he said. There was also no map of the seafloor in the gulf.

OMG sent a research boat into the Inglefield Gulf in the summer of 2016 to fill in the data gap. The boat’s soundings of ocean temperature and salinity showed a river of meltwater draining out from under Tracy. Because freshwater is more buoyant than the surrounding seawater, as soon as the water escapes from under the glacier, it swirls upward along the glacier’s icy face. The turbulent flow pulls in surrounding subsurface water, which is warm for a polar ocean at about 33 degrees Fahrenheit (0.5 degree Celsius). As it gains volume, the plume spreads like smoke rising from a smokestack.

“Most of the melting happens as the water rises up Tracy’s face,” Willis said. “It eats away at a huge chunk of the glacier.”

Heilprin also has a plume, but its shallower depth limits the plume’s damage in two ways: the plume has a shorter distance to rise and gathers less seawater; and the shallow seawater it pulls in has a temperature of only about 31 degrees Fahrenheit (minus 0.5 degree Celsius). As a result, even though Heilprin is a bigger glacier and more water drains from underneath it than from Tracy, its plume is smaller and colder.

The study produced another surprise by first mapping a ridge, called a sill, only about 820 feet (250 meters) below the ocean surface in front of Tracy, and then proving that this sill did not keep warm water from the ocean depths away from the glacier. “In fact, quite a lot of warm water comes in from offshore, mixes with the shallower layers and comes over the sill,” Willis said. Tracy’s destructive plume is evidence of that.