Glacial history affects shape and growth habit of alpine plants

Climate change reflects in the morphology and genes of plants. -  (Image: University of Basel / Jürg Stöcklin)
Climate change reflects in the morphology and genes of plants. – (Image: University of Basel / Jürg Stöcklin)

Alpine plants that survived the Ice Ages in different locations still show accrued differences in appearance and features. These findings were made by botanists from the University of Basel using two plant species. So far, it was only known that the glacial climate changes had left a «genetic fingerprint» in the DNA of alpine plants.

During the Ice Ages the European Alps were covered by a thick layer of ice. Climate fluctuations led to great changes in the occurrences of plants: They survived the cold periods in refugia on the periphery of the Alps which they then repopulated after the ice had drawn back. Such processes in the history of the earth can be detected by molecular analysis as «genetic fingerprints»: refugia and colonization routes can be identified as genetic groups within the plant species. Thus, the postglacial colonization history of alpine plants is still borne in plants alive today.

Yellow Bellflower and Creeping Avens


So far, it was unknown if the Ice Ages also affected the structure and growth habit of alpine plants. Prof. Jürg Stöcklin and his colleagues from the Institute of Botany at the University of Basel were now able to proof this phenomenon in two publications. The glacial periods have left marks on the Yellow Bellflower and the Creeping Avens that are visible to the naked eye. The ancestors of these plants survived the Ice Ages in different glacial refugia which led to the fact that today they show genetic differences in their external morphology and in important functional traits.

Notably, the Yellow Bellflower’s inflorescence and timing of flowering differ between plants from the Eastern Alps and plants from the central or western parts of the Alps. Regarding the Creeping Avens, plants from the Western Alps show significantly more offshoots but have fewer flowers than those from the Eastern Alps, while the dissection of the leaves increases from West to East.

Plants are more adaptable than assumed

The Botanists from Basel further discovered that the variations within one species are partly due to natural selection. For example, the timing of flowering in the Yellow Bellflower can be explained with variability in growing season length. Plants shorten their flowering duration as adaptation to the shorter growing seasons at higher elevations.

«The findings are important for understanding the effects that future climate changes may have on plants», says Stöcklin. «The glacial periods have positively affected the intraspecific biodiversity.» Furthermore, the scientists were able to show that plants are more adaptable than has been assumed previously. Climate changes do have an effect on the distribution of species; however, alpine plants also possess considerable skills to genetically adapt to changing environmental conditions.

First evidence that dust and sand deposits in China are controlled by rivers

Northern China holds some of the world's most significant wind-blown dust deposits, known as loess. The origin of this loess-forming dust and its relationship to sand has previously been the subject of considerable debate. -  Royal Holloway University
Northern China holds some of the world’s most significant wind-blown dust deposits, known as loess. The origin of this loess-forming dust and its relationship to sand has previously been the subject of considerable debate. – Royal Holloway University

New research published today in the journal Quaternary Science Reviews has found the first evidence that large rivers control desert sands and dust in Northern China.

Northern China holds some of the world’s most significant wind-blown dust deposits, known as loess. The origin of this loess-forming dust and its relationship to sand has previously been the subject of considerable debate.

The team of researchers led by Royal Holloway University, analysed individual grains of fine wind-blown dust deposited in the Chinese Loess Plateau that has formed thick deposits over the past 2.5 million years. As part of this, they also analysed the Mu Us desert in Inner Mongolia and the Yellow River, one of the world’s longest rivers, to identify links between the dust deposits and nearby deserts and rivers.

The results showed that the Yellow River transports large quantities of sediment from northern Tibet to the Mu Us desert and further suggests that the river contributes a significant volume of material to the Loess Plateau.

“The Yellow River drains the northeast Tibetan plateau and so the uplift of this region and the development of Yellow River drainage seems to control the large scale dust deposits and sand formation in this part of China,” said lead researcher Tom Stevens from the Department of Geography at Royal Holloway.

“Identifying how this dust is formed and controlled is important, since it drives climate change and ocean productivity and impacts human health. Its relationship to the river and Tibet implies strong links between tectonics and climate change. This suggests that global climate change caused by atmospheric dust may be influenced by the uplift of Tibet and changes in major river systems that drain this area.”

Iron in the Earth’s core weakens before melting

The iron in the Earth’s inner core weakens dramatically before it melts, explaining the unusual properties that exist in the moon-sized solid centre of our planet that have, up until now, been difficult to understand.

Scientists use seismic waves – pulses of energy generated during earthquakes – to measure what is happening in the Earth’s inner core, which at 6000 km beneath our feet is completely inaccessible.

Problematically for researchers, the results of seismic measurements consistently show that these waves move through the Earth’s solid inner core at much slower speeds than predicted by experiments and simulations.

Specifically, a type of seismic wave called a ‘shear wave’ moves particularly slowly through the Earth’s core relative to the speed expected for the material – mainly iron – from which the core is made. Shear waves move through the body of the object in a transverse motion – like waves in a rope, as opposed to waves moving through a slinky spring.

Now, in a paper published in Science, scientists from UCL have proposed a possible explanation. They suggest that the iron in the Earth’s core may weaken dramatically just before melting, becoming much less stiff. The team used quantum mechanical calculations to evaluate the wave velocities of solid iron at inner-core pressure up to melting.

They calculated that at temperatures up to 95% of what is needed to melt iron in the Earth’s inner core, the speed of the seismic waves moving through the inner core decreases linearly but, after 95%, it drops dramatically.

At about 99% of the melting temperature of iron, the team’s calculated velocities agree with seismic data for the Earth’s inner core. Since independent geophysical results suggest that the inner core is likely to be at 99-100% of its melting temperature, the results presented in this paper give a compelling explanation as to why the seismic wave velocities are lower than those predicted previously.

Professor Lidunka Vočadlo, from the UCL department of Earth Sciences and an author of the paper said: “The Earth’s deep interior still holds many mysteries that scientists are trying to unravel.

“The proposed mineral models for the inner core have always shown a faster wave speed than that observed in seismic data. This mismatch has given rise to several complex theories about the state and evolution of the Earth’s core.”

The authors stress that this is not the end of the story as other factors need to be taken into account before a definitive core model can be made. As well as iron, the core contains nickel and light elements, such as silicon and sulphur.

Professor Vočadlo said: “The strong pre-melting effects in iron shown in our paper are an exciting new development in understanding the Earth’s inner core. We are currently working on how this result is affected by the presence of other elements, and we may soon be in a position to produce a simple model for the inner core that is consistent with seismic and other geophysical measurements.

Crystals in Picabo’s rocks point to ‘recycled’ super-volcanic magma chambers

University of Oregon geologist Ilya Bindeman, left, and graduate student Dana Drew, working in Bindeman's stable isotope laboratory say that the composition of zircon bits in igneous rocks in the Yellowstone hotspot track tell a new story on how super volcanoes recycle magma. -  University of Oregon
University of Oregon geologist Ilya Bindeman, left, and graduate student Dana Drew, working in Bindeman’s stable isotope laboratory say that the composition of zircon bits in igneous rocks in the Yellowstone hotspot track tell a new story on how super volcanoes recycle magma. – University of Oregon

A thorough examination of tiny crystals of zircon, a mineral found in rhyolites, an igneous rock, from the Snake River Plain has solidified evidence for a new way of looking at the life cycle of super-volcanic eruptions in the long track of the Yellowstone hotspot, say University of Oregon scientists.

The pattern emerging from new and previous research completed in the last five years under a National Science Foundation career award, said UO geologist Ilya N. Bindeman, is that another super-eruption from the still-alive Yellowstone volcanic field is less likely for the next few million years than previously thought (see related story, “Not in a million years, says Oregon geologist about Yellowstone eruption“). The last eruption 640,000 years ago created the Yellowstone Caldera and the Lava Creek Tuff in what is now Yellowstone National Park.

The Yellowstone hotspot creates a conveyor belt style of volcanism because of the southwest migration of the North American plate at 2-4 centimeters (about .8 to 1.6 inches) annually over the last 16 million years of volcanism. Due to the movement of the North American plate, the plume interaction with the crust leaves footprints in the form of caldera clusters, in what is now the Snake River Plain, Bindeman said.

The Picabo volcanic field of southern Idaho, described in a new paper by a six-member team, was active between 10.4 and 6.6 million years ago and experienced at least three, and maybe as many as six, violent caldera-forming eruptions. The field has been difficult to assess, said lead author Dana Drew, a UO graduate student, because the calderas have been buried by as much as two kilometers of basalt since its eruption cycle died.

The work at Picabo is detailed in a paper online ahead of publication in the journal Earth and Planetary Science Letters.

The team theorized that basalt from the mantle plume, rocks from Earth’s crust and previously erupted volcanoes are melted together to form the rhyolites erupted in the Snake River Plain. Before each eruption, rhyolite magma is stored in dispersed pockets throughout the upper crust, which are later mixed together, according to geochemical evidence. “We think that this batch-assembly process is an important part of caldera-forming eruptions, and generating rhyolites in general,” Drew said.

In reaching their conclusions, Drew and colleagues analyzed radiogenic and stable isotopic data — specifically oxygen and hafnium — in zircons detected in rhyolites found at the margins of the Picabo field and from a deep borehole. That data, in combination with whole rock geochemistry and zircon uranium-lead geochronology helped provide a framework to understand the region’s ancient volcanic past.

Previous research on the related Heise volcanic field east of Picabo yielded similar results. “There is a growing database of the geochemistry of rhyolites in the Yellowstone hotspot track,” Drew said. “Adding Picabo provides a missing link in the database.

Drew and colleagues, through their oxygen isotope analyses, identified a wide diversity of oxygen ratios occurring in erupted zircons near the end of the Picabo volcanic cycle. Such oxygen ratios are referred to as delta-O-18 signatures based on oxygen 18 levels relative to seawater. (Oxygen 18 contains eight protons and 10 neutrons; Oxygen 16, with eight protons and eight neutrons, is the most commonly found form of oxygen in nature)

The approach provided a glimpse into the connection of surface and subsurface processes at a caldera cluster. The interaction of erupted rhyolite with groundwater and surface water causes hydrothermal alteration and the change in oxygen isotopes, thereby providing a fingerprinting tool for the level of hydrothermal alteration, Drew said.

“Through the eruptive sequence, we begin to generate lower delta-O-18 signatures of the magmas and, with that, we also see a more diverse signature,” Drew said. “By the time of the final eruption there is up to five per mil diversity in the signature recorded in the zircons.” The team attributes these signatures to the mixing of diverse magma batches dispersed in the upper crust, which were formed by melting variably hydrothermally altered rocks — thus diverse delta-O-18 — after repeated formation of calderas and regional extension or stretching of the crust.

When the pockets of melt are rapidly assembled, the process could be the trigger for caldera forming eruptions, Bindeman said. “That leads to a homogenized magma, but in a way that preserves these zircons of different signatures from the individual pockets of melt,” he said. This research, he added, highlights the importance of using new micro-analytical isotopic techniques to relate geochemistry at the crystal-scale to processes occurring at the crustal-wide scale in generating and predicting large-volume rhyolitic eruptions.

“This important research by Dr. Bindeman and his team demonstrates the enormous impact an NSF CAREER award can have,” said Kimberly Andrews Espy, vice president for research and innovation and dean of the graduate school at the University of Oregon. “The five-year project is providing new insights into the eruption cycles of the Yellowstone hotspot and helping scientists to better predict future volcanic activity.”

3D model reveals new information about iconic volcano

The volcano on the Scottish peninsula Ardnamurchan is a popular place for the study of rocks and structures in the core of a volcano. Geology students read about it in text books and geologists have been certain that the Ardnamurchan volcano have three successive magma chambers. However, an international group of researchers, lead from Uppsala University, Sweden, has now showed that the volcano only has one single magma chamber.

The new study is published in Scientific Reports, the new open access journal of the Nature Publishing Group.

The 58 million year old Ardnamurchan volcano is an iconic site for the study of rocks and structures in the core of a volcano, which is why thousands of geology students from all over the world visit Ardnamurchan every year. Since the early days of modern geology the Ardnamurchan volcano is believed to have had three successive magma chambers (or centres) that fed hundreds of thin arcuate basalt intrusions, so-called cone sheets, that are exposed all over the peninsula.

The researchers from the universities of Uppsala (Sweden), Quebec (Canada), Durham and St. Andrews (UK), challenges the 3-centre concept using a 3D model of the subsurface beneath today’s land surface. According to this model, the Ardnamurchan volcano was underlain by a single but elongate magma chamber.

Studying extinct volcanoes is a way for geologists to understand the interior of volcanic edifices and to gain knowledge on the processes that occur within active volcanoes today. It is therefore that the volcanic centres of western Scotland and northeastern Ireland were intensely studied by British geologists in the late 19th and early 20th century. It was in these eroded volcanoes that the foundation for modern volcanology was laid. Ardnamurchan in particular has an iconic status among geologists everywhere in the world. Geology students read about it in text books and visit it during field excursions.

“It came as a bit of a surprise to us that there is still so much to learn from a place that has received so much attention by geologists, in particular since we used the original data collected in 1930 by Richey and Thomas.” said Dr Steffi Burchardt, senior lecturer at Uppsala University.

“Modern software allows visualizing field measurements in 3D and opens up a range of new perspectives. After projecting hundreds of cone sheets in the computer model, we were unable to identify three separate centres. The cone sheets instead appear to originate from a single, large, and elongate magma chamber about 1.5 km below today’s land surface.”

This magma chamber beneath Ardnamurchan was up to 6 km long and has the shape of an elongate saucer.

“These types of magma chambers are known to exist for example within volcanoes in Iceland have have been detected in the North Sea bedrock. Ardnamurchan’s new magma chamber is hence much more realistic considering everything we have learned about Ardnamurchan and other extinct and active volcanoes since the time of Richey and Thomas” said Prof. Valentin Troll, chair in petrology at Uppsala University.

Water and lava, but — curiously — no explosion

Researchers say pillars like these were formed when lava and water met on land without exploding. -  Tracy Gregg
Researchers say pillars like these were formed when lava and water met on land without exploding. – Tracy Gregg

Rocky pillars dotting Iceland’s Skaelingar valley were projectiles tossed into the fields by warring trolls. That, at least, is the tale that University at Buffalo geologist Tracy Gregg heard from a tour guide and local hiker when she visited the site on two occasions.

But Gregg and a colleague have a new explanation for the presence of the lava formations – this one also unexpected.

In the Journal of Volcanology and Geothermal Research, she and former UB master’s student Kenneth Christle report that the pillars, hollow and made from basalt, likely formed in a surprising reaction where lava met water without any explosion occurring. Their findings appeared online Aug. 15 and will be published in a forthcoming print edition of the journal.

“Usually, when lava and water meet in aerial environments, the water instantly flashes to steam,” said Gregg, a UB associate professor of geology. “That’s a volume increase of eight times – boom.”

“Formations like the ones we see in Iceland are common in the ocean under two miles of water, where there’s so much pressure that there’s no explosion,” she said. “They’ve never been described on land before, and it’s important because it tells us that water and lava can come together on land and not explode. This has implications for the way we view volcanic risk.”

Deep-sea basalt pillars form when columns of super-heated water rise between pillows of lava on the ocean floor, cooling the molten rock into hollow, pipe-like minarets. The structures grow taller as lava levels rise, and remain standing even after volcanic eruptions end and lava levels fall again.

Gregg and Christle propose that the same phenomenon sculpted the land-based lava pillars in Iceland.

It happened in the 1780s, when lava from a nearby eruption entered the Skaelingar valley, which Gregg theorizes was covered by a pond or was super-swampy. She thinks one reason no explosion occurred was because the lava was moving so slowly – centimeters per second – that it was able to react with the water in a “kinder, gentler” manner.

“If you’re driving your car at 5 miles per hour and you hit a stop sign, it’s a lot different than if you hit that same stop sign at 40 miles an hour,” she said. “There’s a lot more energy that will be released.”

The Iceland formations, some over 2 meters tall, display telltale features that hint at how they were created. For example:

  • They are hollow on the inside.

  • Their rocky exteriors bear vertical scars – scratches where pieces of floating crust may have rammed into the pillars and scraped the surface as lava levels in the valley declined.

  • The skin of the towers isn’t smooth, but gnarled with shiny drips of rock. The glassy texture suggests that the lava hardened quickly into rock, at a pace consistent with non-explosive water-lava interactions. Had the lava cooled more slowly in air, it would have formed crystals.

Each of these distinctive characteristics is also prevalent in deep-ocean pillars, said Gregg, who first saw the Icelandic formations in the mid-1990s while hiking in the valley with her husband.

“I knew as soon as I saw them what they were,” she said. “I had, at that time, been on submarine cruises and seen these things deep under the sea, so I was just hysterical, saying, ‘Look at these!’ So I ran around and started taking pictures until the light started running out.”

She didn’t have the chance to return to the site until 2010, when Christle received a student research grant from the Geological Society of America to do field work in Iceland. The two spent four days studying the pillars in detail, confirming Gregg’s original suspicions.

In the future, scientists could hunt for land-based lava pillars near oceans to learn about the height of ancient seas, or search for such formations on Mars and other planets to determine where water once existed.

First ever evidence of a comet striking Earth

This is an artist's rendition of the comet exploding in Earth's atmosphere above Egypt. -  Terry Bakker
This is an artist’s rendition of the comet exploding in Earth’s atmosphere above Egypt. – Terry Bakker

The first ever evidence of a comet entering Earth’s atmosphere and exploding, raining down a shock wave of fire which obliterated every life form in its path, has been discovered by a team of South African scientists and international collaborators.

The discovery has not only provided the first definitive proof of a comet striking Earth, millions of years ago, but it could also help us to unlock, in the future, the secrets of the formation of our solar system.

“Comets always visit our skies – they’re these dirty snowballs of ice mixed with dust – but never before in history has material from a comet ever been found on Earth,” says Professor David Block of Wits University.

The comet entered Earth’s atmosphere above Egypt about 28 million years ago. As it entered the atmosphere, it exploded, heating up the sand beneath it to a temperature of about 2 000 degrees Celsius, and resulting in the formation of a huge amount of yellow silica glass which lies scattered over a 6 000 square kilometre area in the Sahara. A magnificent specimen of the glass, polished by ancient jewellers, is found in Tutankhamun’s brooch with its striking yellow-brown scarab.

The research, which will be published in Earth and Planetary Science Letters, was conducted by a collaboration of geoscientists, physicists and astronomers including Block, lead author Professor Jan Kramers of the University of Johannesburg, Dr Marco Andreoli of the South African Nuclear Energy Corporation, and Chris Harris of the University of Cape Town.

At the centre of the attention of this team was a mysterious black pebble found years earlier by an Egyptian geologist in the area of the silica glass. After conducting highly sophisticated chemical analyses on this pebble, the authors came to the inescapable conclusion that it represented the very first known hand specimen of a comet nucleus, rather than simply an unusual type of meteorite.

Kramers describes this as a moment of career defining elation. “It’s a typical scientific euphoria when you eliminate all other options and come to the realisation of what it must be,” he said.

The impact of the explosion also produced microscopic diamonds. “Diamonds are produced from carbon bearing material. Normally they form deep in the earth, where the pressure is high, but you can also generate very high pressure with shock. Part of the comet impacted and the shock of the impact produced the diamonds,” says Kramers.

The team have named the diamond-bearing pebble “Hypatia” in honour of the first well known female mathematician, astronomer and philosopher, Hypatia of Alexandria.

Comet material is very elusive. Comet fragments have not been found on Earth before except as microscopic sized dust particles in the upper atmosphere and some carbon-rich dust in the Antarctic ice. Space agencies have spent billions to secure the smallest amounts of pristine comet matter.

“NASA and ESA (European Space Agency) spend billions of dollars collecting a few micrograms of comet material and bringing it back to Earth, and now we’ve got a radical new approach of studying this material, without spending billions of dollars collecting it,” says Kramers.

The study of Hypatia has grown into an international collaborative research programme, coordinated by Andreoli, which involves a growing number of scientists drawn from a variety of disciplines. Dr Mario di Martino of Turin’s Astrophysical Observatory has led several expeditions to the desert glass area.

“Comets contain the very secrets to unlocking the formation of our solar system and this discovery gives us an unprecedented opportunity to study comet material first hand,” says Block.

Clues to foam formation could help find oil

In one of two bubble-forming mechanisms discovered at Rice University, a bubble is split before entering a constriction by a neighboring bubble and the wall. The research is part of Rice's effort to understand the creation of foam for enhanced oil extraction and other purposes. -  Biswal Lab/Rice University
In one of two bubble-forming mechanisms discovered at Rice University, a bubble is split before entering a constriction by a neighboring bubble and the wall. The research is part of Rice’s effort to understand the creation of foam for enhanced oil extraction and other purposes. – Biswal Lab/Rice University

Blowing bubbles in the backyard is one thing and quite another when searching for oil. That distinction is at the root of new research by Rice University scientists who describe in greater detail than ever precisely how those bubbles form, evolve and act.

A new study led by Rice chemical and biomolecular engineer Sibani Lisa Biswal and published in the journal Soft Matter describes two previously unknown ways that bubbles form in foam.

The work should be of interest to those who make and use foam for a variety of reasons, from shaving cream to insulation. But it may be of primary importance to companies trying to extract every possible drop of oil from a reservoir by using volumes of thick foam to displace it.

Biswal and her team used microfluidic devices and high-speed imaging to capture images of how bubbles transform as they pass through tight spaces like those found in permeable rock deep underground. They discovered mechanisms that should help engineers understand how foam can be manipulated for specific tasks.

“In the classic descriptions of bubble formation, there’s what we call snap-off, lamella division and leave-behind,” Biswal said. Snap-off bubbles are created when liquid accumulates by capillary action in a narrow section of a pore and forms a liquid slug separating two bubbles. A lamella division bubble happens when the lamella (a thin film of liquid) moves through a branch in the flow path and becomes two lamella. Leave-behind happens when a gas enters two adjoining, parallel pores and the liquid between the two pores thin down to a lamella.

In the newly observed bubble-making processes, which she calls “pinch-off” behaviors, the bubbles form before gas passes through the constriction, not after.

“No one has seen these mechanisms,” she said. In one pinch-off, a bubble caught between a neighboring bubble and the wall would split as it entered the channel. In the second, she said, “We found neighboring bubbles that are basically karate-chopping a third one as it tries to go through.”

The smaller the bubbles in the foam, the better it may serve enhanced oil recovery, said George Hirasaki, a Rice research professor of chemical and biomolecular engineering and co-author of the paper.

“We’re trying to understand how foam behaves in porous media because it is a way of making gas act like a more viscous fluid,” he said. “Normally, gas has very low viscosity and it tends to flow through rock and not displace oil and water. Once it finds a path, usually along the top of a reservoir, the rest of the gas tends to follow.

“If there were some way to make gas act more like a liquid, to make it more viscous, then it would contact much more of the reservoir and would push the fluids out,” Hirasaki said.

Ideally, foam would pack the channels inside high-permeable regions and force pressure to flow through rocks with low permeability, flushing out the hard-to-get oil often trapped there.

The Biswal lab built devices that mimic what happens in porous rock, squeezing mixtures of gas and surfactant through 20 micrometer-wide channels. They filmed what happened under a range of pressures at either end of the channel at 10,000 frames per second.

“Normally we work in rock samples or sand packs and we measure the pressure drop,” Hirasaki said. “It’s hard to see what’s happening at the pore scale. But with the micromodel, we can see it with our own eyes – or with the camera’s eye.”

“We want to offer the oil industry more mobility control,” Biswal said. “What we mean by that is the ability to drive fluids through areas that vary in their permeability. We want fluids to move through the entire path, not just the path of least resistance.”

Lead authors are Rice alumna Rachel Liontas, currently a graduate student at Caltech, and former graduate student Kun Ma, currently a reservoir engineer at Total E&P USA. Biswal is an associate professor of chemical and biomolecular engineering.

Iron melt network helped grow Earth’s core, study suggests

The same process that allows water to trickle through coffee grinds to create your morning espresso may have played a key role in the formation of the early Earth and influenced its internal organization, according to a new study by scientists at Stanford’s School of Earth Sciences.

The finding, published in the current issue of the journal Nature Geoscience, lends credence to a theory first proposed nearly half a century ago suggesting that Earth’s iron-rich core and layered internal structure might have formed in a series of steps that took place over millions of years under varying temperature and pressure conditions.

“We know that Earth today has a core and a mantle that are differentiated. With improving technology, we can look at different mechanisms of how this came to be in a new light,” said study leader Wendy Mao, an assistant professor of geological and environmental sciences at Stanford, and of photon sciences at the SLAC National Accelerator Laboratory, which is operated by the university.

Earth’s innards are presently divided into layers, with the rocky mantle composed mostly of silicates overlying an iron-rich metallic core. How the planet came to have this orderly arrangement is a major mystery, especially since scientists think its beginnings were messy and chaotic, the result of small bodies made up of rock and metals crashing and clumping together shortly after the formation of the sun and the birth of the solar system some 4.5 billion years ago.

How did Earth evolve from this conglomerated mass of rocks and metals into its current layered state?

Separating metal from rock


One idea is that the heat generated by the collisions and by the radioactive decay of certain isotopes warmed the Earth. The planet could have gotten so hot that its rocks and metals melted. The molten rocks and metals in this “magma ocean” would then have separated into distinct layers as a result of their different densities. Iron would have drifted downward towards the planet’s center, while silicates remained on top.

Other scientists have proposed that even if the early Earth’s temperature was not hot enough to melt silicates, the molten iron might still have separated out by percolating through the solid silicate layer.

The thought was that pockets of molten iron trapped in the mantle layer could tunnel through the surrounding rock to create channels, or capillaries. This network of tunnels could have helped funnel molten iron towards the planet’s center to join the spherical metallic heart that was slowly amassing there.

However, this “percolation” theory was dealt a major blow when scientists discovered that, in the upper mantle layer at least, the molten iron tended to form isolated spheres that didn’t interact with one another, similar to the way water beads up on a waxed surface.

For this reason, scientists had previously thought that percolation couldn’t be possible, Mao said.

Recreating ancient Earth

But a new experiment conducted by Mao and her team uncovered fresh evidence that percolation might still be a viable mechanism for explaining the formation of Earth’s core.

Working with researchers at the U.S. Department of Energy’s SLAC facility, Mao and her team recreated a speck of the molten silicate and iron material that scientists believe existed deep inside the early Earth.

To do this, Mao’s team placed minute amounts of iron and silicate rock into a metal chamber that they then inserted between the tips of two small diamonds. Squeezing these “diamond anvils” together recreated the immense pressures present in the Earth’s interior, and a laser beam was used to heat the sample to a high enough temperature to melt the iron.

After the sample cooled, the scientists examined it using X-ray-computed tomography. Tomography creates a three-dimensional image of an object by combining a series of two-dimensional slices. A computer program then helps flesh out the re-creation of the object.

A state-of-the-art X-ray microscope at SLAC allowed Mao’s team to resolve nanometer-scale details in their sample of heated silicates and iron. The higher resolution allowed the scientists to observe never-before-seen changes in the texture and shape of the molten iron and silicates as they responded to the same intense pressures and temperatures that were present deep in the early Earth.

Which happened first?


The experiment confirmed the findings from previous studies that molten iron in the upper mantle tended to form isolated blobs, which would have prevented percolation from happening. “In order for percolation to be efficient, the molten iron needs to be able to form continuous channels through the solid,” Mao explained.

However, the scientists found that at the higher pressures and temperatures that would have been present in the early Earth’s lower mantle, the structure of the silicates changed in a way that permitted connections to form between pockets of molten iron, making percolation possible.

“Scientists had said this theory wasn’t possible, but now we’re saying, under certain conditions that we know exist in the planet, it could happen,” Mao said. “So this brings back another possibility for how the core might have formed.”

The team’s new findings do not rule out the possibility that differentiation began when Earth was in a magma ocean state. In fact, both mechanisms could have occurred, said study first author Crystal Shi, a graduate student in Mao’s lab.

“We don’t know which mechanism happened first, or if the two happened together,” Shi said. “At the very beginning, Earth would have still been very hot, and the magma ocean mechanism could have been important. But later as the planet cooled, percolation may have become the dominant mechanism.”

Extrusive volcanism formed the Hawaiian Islands

This is a 3-D perspective view of the topography of the Hawaiian Islands (gray shaded) and seafloor relief viewed from just south of the Hawaii's Big Island. The colors show residual gravity anomaly, measured on land and along ship tracks: red-cyan representing an excess pull of gravity, blue representing a small deficit in the pull of gravity. -  Ashton Flinders, UHM SOEST.
This is a 3-D perspective view of the topography of the Hawaiian Islands (gray shaded) and seafloor relief viewed from just south of the Hawaii’s Big Island. The colors show residual gravity anomaly, measured on land and along ship tracks: red-cyan representing an excess pull of gravity, blue representing a small deficit in the pull of gravity. – Ashton Flinders, UHM SOEST.

A recent study by researchers at the University of Hawaii – Manoa (UHM) School of Ocean and Earth Science and Technology (SOEST) and the University of Rhode Island (URI) changes the understanding of how the Hawaiian Islands formed. Scientists have determined that it is the eruptions of lava on the surface, extrusion, which grow Hawaiian volcanoes, rather than internal emplacement of magma, as was previously thought.

Before this work, most scientists thought that Hawaiian volcanoes grew primarily internally – by magma intruding into rock and solidifying before it reaches the surface. While this type of growth does occur, along Kilauea’s East Rift Zone (ERZ), for example, it does not appear to be representative of the overall history of how the Hawaiian Islands formed. Previous estimates of the internal-to-extrusive ratios (internally emplaced magma versus extrusive lava flow) were based on observations over a very short time frame, in the geologic sense.

Ashton Flinders (M.S. from UHM), lead author and graduate student at URI, and colleagues compiled historical land-based gravity surveys with more recent surveys on the Big Island of Hawaii (in partnership with Jim Kauhikaua of the U.S. Geological Survey – Hawaii Volcano Observatory) and Kauai, along with marine surveys from the National Geophysical Data Center and from the UH R/V Kilo Moana. These types of data sets allow scientists to infer processes that have taken place over longer time periods.

“The discrepancy we see between our estimate and these past estimates emphasizes that the short term processes we currently see in Hawaii (which tend to be more intrusive) do not represent the predominant character of their volcanic activity,” said Flinder.

“This could imply that over the long-term, Kilauea’s ERZ will see less seismic activity and more eruptive activity that previously thought. The 3-decade-old eruption along Kilauea’s ERZ could last for many, many more decades to come,” said Dr. Garrett Ito, Professor of Geology and Geophysics at UHM and co-author.

“I think one of the more interesting possible implications is how the intrusive-to-extrusive ratio impacts the stability of the volcano’s flank. Collapses occur over a range of scales from as large as the whole flank of a volcano, to bench collapses on the south coast of Big Island, to small rock falls. ” said Flinders. Intrusive magma is more dense and structurally stronger than lava flows. “If the bulk of the islands are made from these weak extrusive flows then this would account for some of the collapses that have been documented, but this is mainly just speculation as of now.”

The authors hope this new density model can be used as a starting point for further crustal studies in the Hawaiian Islands.