No Redoubt: Volcanic eruption forecasting improved

Forecasting volcanic eruptions with success is heavily dependent on recognizing well-established patterns of pre-eruption unrest in the monitoring data. But in order to develop better monitoring procedures, it is also crucial to understand volcanic eruptions that deviate from these patterns.

New research from a team led by Carnegie’s Diana Roman retrospectively documented and analyzed the period immediately preceding the 2009 eruption of the Redoubt volcano in Alaska, which was characterized by an abnormally long period of pre-eruption seismic activity that’s normally associated with short-term warnings of eruption. Their work is published today by Earth and Planetary Science Letters.

Well-established pre-eruption patterns can include a gradual increase in the rate of seismic activity, a progressive alteration in the type of seismic activity, or a change in ratios of gas released.

“But there are numerous cases of volcanic activity that in some way violated these common patterns of precursory unrest,” Roman said. “That’s why examining the unusual precursor behavior of the Redoubt eruption is so enlightening.”

About six to seven months before the March 2009 eruption, Redoubt began to experience long-period seismic events, as well as shallow volcanic tremors, which intensified into a sustained tremor over the next several months. Immediately following this last development, shallow, short-period earthquakes were observed at an increased rate below the summit. In the 48 hours prior to eruption both deep and shallow earthquakes were recorded.

This behavior was unusual because precursor observations usually involve a transition from short-period to long-period seismic activity, not the other way around. What’s more, seismic tremor is usually seen as a short-term warning, not something that happens months in advance. However, these same precursors were also observed during the 1989-90 Redoubt eruption, thus indicating that the unusual seismic pattern reflects some unique aspect of the volcano’s magma system.

Advanced analysis of the seismic activity taking place under the volcano allowed Roman and her team to understand the changes taking place before, during, and after eruption. Their results show that the eruption was likely preceded by a protracted period of slow magma ascent, followed by a short period of rapidly increasing pressure beneath Redoubt.

Elucidating the magma processes causing these unusual precursor events could help scientists to hone their seismic forecasting, rather than just relying on the same forecasting tools they’re currently using, ones that are not able to detect anomalies.

For example, using current techniques, the forecasts prior to Redoubt’s 2009 eruption wavered over a period of five months, back and forth between eruption being likely within a few weeks to within a few days. If the analytical techniques used by Roman and her team had been taken into consideration, the early risk escalations might not have been issued.

“Our work shows the importance of clarifying the underlying processes driving anomalous volcanic activity. This will allow us to respond to subtle signals and increase confidence in making our forecasts.” Roman said.

No Redoubt: Volcanic eruption forecasting improved

Forecasting volcanic eruptions with success is heavily dependent on recognizing well-established patterns of pre-eruption unrest in the monitoring data. But in order to develop better monitoring procedures, it is also crucial to understand volcanic eruptions that deviate from these patterns.

New research from a team led by Carnegie’s Diana Roman retrospectively documented and analyzed the period immediately preceding the 2009 eruption of the Redoubt volcano in Alaska, which was characterized by an abnormally long period of pre-eruption seismic activity that’s normally associated with short-term warnings of eruption. Their work is published today by Earth and Planetary Science Letters.

Well-established pre-eruption patterns can include a gradual increase in the rate of seismic activity, a progressive alteration in the type of seismic activity, or a change in ratios of gas released.

“But there are numerous cases of volcanic activity that in some way violated these common patterns of precursory unrest,” Roman said. “That’s why examining the unusual precursor behavior of the Redoubt eruption is so enlightening.”

About six to seven months before the March 2009 eruption, Redoubt began to experience long-period seismic events, as well as shallow volcanic tremors, which intensified into a sustained tremor over the next several months. Immediately following this last development, shallow, short-period earthquakes were observed at an increased rate below the summit. In the 48 hours prior to eruption both deep and shallow earthquakes were recorded.

This behavior was unusual because precursor observations usually involve a transition from short-period to long-period seismic activity, not the other way around. What’s more, seismic tremor is usually seen as a short-term warning, not something that happens months in advance. However, these same precursors were also observed during the 1989-90 Redoubt eruption, thus indicating that the unusual seismic pattern reflects some unique aspect of the volcano’s magma system.

Advanced analysis of the seismic activity taking place under the volcano allowed Roman and her team to understand the changes taking place before, during, and after eruption. Their results show that the eruption was likely preceded by a protracted period of slow magma ascent, followed by a short period of rapidly increasing pressure beneath Redoubt.

Elucidating the magma processes causing these unusual precursor events could help scientists to hone their seismic forecasting, rather than just relying on the same forecasting tools they’re currently using, ones that are not able to detect anomalies.

For example, using current techniques, the forecasts prior to Redoubt’s 2009 eruption wavered over a period of five months, back and forth between eruption being likely within a few weeks to within a few days. If the analytical techniques used by Roman and her team had been taken into consideration, the early risk escalations might not have been issued.

“Our work shows the importance of clarifying the underlying processes driving anomalous volcanic activity. This will allow us to respond to subtle signals and increase confidence in making our forecasts.” Roman said.

Ancient Earth crust stored in deep mantle

Scientists have long believed that lava erupted from certain oceanic volcanoes contains materials from the early Earth’s crust. But decisive evidence for this phenomenon has proven elusive. New research from a team including Carnegie’s Erik Hauri demonstrates that oceanic volcanic rocks contain samples of recycled crust dating back to the Archean era 2.5 billion years ago. Their work is published in Nature.

Oceanic crust sinks into the Earth’s mantle at so-called subduction zones, where two plates come together. Much of what happens to the crust during this journey is unknown. Model-dependent studies for how long subducted material can exist in the mantle are uncertain and evidence of very old crust returning to Earth’s surface via upwellings of magma has not been found until now.

The research team studied volcanic rocks from the island of Mangaia in Polynesia’s Cook Islands that contain iron sulfide inclusions within crystals. In-depth analysis of the chemical makeup of these samples yielded interesting results.

The research focused on isotopes of the element sulfur. (Isotopes are atoms of the same element with different numbers of neutrons.) The measurements, conducted by graduate student Rita Cabral, looked at three of the four naturally occurring isotopes of sulfur–isotopic masses 32, 33, and 34. The sulfur-33 isotopes showed evidence of a chemical interaction with UV radiation that stopped occurring in Earth’s atmosphere about 2.45 billion years ago. It stopped after the Great Oxidation Event, a point in time when the Earth’s atmospheric oxygen levels skyrocketed as a consequence of oxygen-producing photosynthetic microbes. Prior to the Great Oxidation Event, the atmosphere lacked ozone. But once ozone was introduced, it started to absorb UV and shut down the process.

This indicates that the sulfur comes from a deep mantle reservoir containing crustal material subducted before the Great Oxidation Event and preserved for over half the age of the Earth.

“These measurements place the first firm age estimates of recycled material in oceanic hotspots,” Hauri said. “They confirm the cycling of sulfur from the atmosphere and oceans into mantle and ultimately back to the surface,” Hauri said.

Ancient Earth crust stored in deep mantle

Scientists have long believed that lava erupted from certain oceanic volcanoes contains materials from the early Earth’s crust. But decisive evidence for this phenomenon has proven elusive. New research from a team including Carnegie’s Erik Hauri demonstrates that oceanic volcanic rocks contain samples of recycled crust dating back to the Archean era 2.5 billion years ago. Their work is published in Nature.

Oceanic crust sinks into the Earth’s mantle at so-called subduction zones, where two plates come together. Much of what happens to the crust during this journey is unknown. Model-dependent studies for how long subducted material can exist in the mantle are uncertain and evidence of very old crust returning to Earth’s surface via upwellings of magma has not been found until now.

The research team studied volcanic rocks from the island of Mangaia in Polynesia’s Cook Islands that contain iron sulfide inclusions within crystals. In-depth analysis of the chemical makeup of these samples yielded interesting results.

The research focused on isotopes of the element sulfur. (Isotopes are atoms of the same element with different numbers of neutrons.) The measurements, conducted by graduate student Rita Cabral, looked at three of the four naturally occurring isotopes of sulfur–isotopic masses 32, 33, and 34. The sulfur-33 isotopes showed evidence of a chemical interaction with UV radiation that stopped occurring in Earth’s atmosphere about 2.45 billion years ago. It stopped after the Great Oxidation Event, a point in time when the Earth’s atmospheric oxygen levels skyrocketed as a consequence of oxygen-producing photosynthetic microbes. Prior to the Great Oxidation Event, the atmosphere lacked ozone. But once ozone was introduced, it started to absorb UV and shut down the process.

This indicates that the sulfur comes from a deep mantle reservoir containing crustal material subducted before the Great Oxidation Event and preserved for over half the age of the Earth.

“These measurements place the first firm age estimates of recycled material in oceanic hotspots,” Hauri said. “They confirm the cycling of sulfur from the atmosphere and oceans into mantle and ultimately back to the surface,” Hauri said.

Rethinking early atmospheric oxygen

This photo shows researchers doing field sampling of a pyrite-rich black shale outcrop in China. The weathering of such sediments, which contain sulfur originally buried from the ocean, transfers sulfur isotope signals to the ocean to be buried again in marine sediments. -  Chu Research Group, Institute of Geology and Geophysics, Chinese Academy of Sciences.
This photo shows researchers doing field sampling of a pyrite-rich black shale outcrop in China. The weathering of such sediments, which contain sulfur originally buried from the ocean, transfers sulfur isotope signals to the ocean to be buried again in marine sediments. – Chu Research Group, Institute of Geology and Geophysics, Chinese Academy of Sciences.

A research team of biogeochemists at the University of California, Riverside has provided a new view on the relationship between the earliest accumulation of oxygen in the atmosphere, arguably the most important biological event in Earth history, and its relationship to the sulfur cycle.

A general consensus exists that appreciable oxygen first accumulated in Earth’s atmosphere around 2.4 to 2.3 billion years ago. Though this paradigm is built upon a wide range of geological and geochemical observations, the famous “smoking gun” for what has come to be known as the “Great Oxidation Event” (GOE) comes from the disappearance of anomalous fractionations in rare sulfur isotopes.

“These isotope fractionations, often referred to as ‘mass-independent fractionations,’ or ‘MIF’ signals, require both the destruction of sulfur dioxide by ultraviolet energy from the sun in an atmosphere without ozone and very low atmospheric oxygen levels in order to be transported and deposited in marine sediments,” said Christopher T. Reinhard, the lead author of the research paper and a former UC Riverside graduate student. “As a result, their presence in ancient rocks is interpreted to reflect vanishingly low atmospheric oxygen levels continuously for the first ~2 billion years of Earth’s history.”

However, diverse types of data are emerging that point to the presence of atmospheric oxygen, and, by inference, the early emergence of oxygenic photosynthesis hundreds of millions of years before these MIF signals disappear from the rock record. These observations motivated Reinhard and colleagues to explore the possible conditions under which inherited MIF signatures may have persisted in the rock record long after oxygen accumulated in the atmosphere.

Using a simple quantitative model describing how sulfur and its isotopes cycle through the Earth’s crust, the researchers discovered that under certain conditions these MIF signatures can persist within the ocean and marine sediments long after O2 increases in the atmosphere. Simply put, the weathering of rocks on the continents can transfer the MIF signal to the oceans and their sediments long after production of this fingerprint has ceased in an oxygenated atmosphere.

“This lag would blur our ability to date the timing of the GOE and would allow for dynamic rising and falling oxygen levels during a protracted transition from an atmosphere without oxygen to one rich in this life-giving gas,” Reinhard said.

Study results appear in Nature‘s advanced online publication on April 24.

Reinhard explained that once MIF signals formed in an oxygen-poor atmosphere are captured in pyrite and other minerals in sedimentary rocks, they are recycled when those rocks are later uplifted as mountain ranges and the pyrite is oxidized.

“Under certain conditions, this will create a sort of ‘memory effect’ of these MIF signatures, providing a decoupling in time between the burial of MIF in sediments and oxygen accumulation at Earth’s surface,” he said.


According to the researchers, the key here is burying a distinct MIF signal in deep sea sediments, which are then subducted and removed from Earth’s surface.

“This would create a complementary signal in minerals that are weathered and delivered to the oceans, something that we actually see evidence of in the rock record,” said Noah Planavsky, the second author of the research paper and a former UC Riverside graduate student now at Caltech. “This signal can then be perpetuated through time without the need to generate it within the atmosphere contemporaneously.”

Reinhard, now a postdoctoral fellow at Caltech and soon to be an assistant professor at Georgia Institute of Technology, explained that although the researchers’ new model provides a plausible mechanism for reconciling recent conflicting data, this can only occur when certain key conditions are met – and these conditions are likely to have changed through time during Earth’s long early history.

“There is obviously much further work to do, but we hope that our model is one step toward a more integrated view of how Earth’s crust, mantle and atmosphere interact in the global sulfur cycle,” he said.

Timothy W. Lyons, a professor of biogeochemistry at UCR and the principal investigator of the research project noted that this is a fundamentally new and potentially very important way of looking at the sulfur isotope record and its relationship to biospheric oxygenation.

“The message is that sulfur isotope records, when viewed through the filter of sedimentary recycling, may challenge efforts to precisely date the GOE and its relationship to early life, while opening the door to the wonderful unknowns we should expect and embrace,” he said.

Rethinking early atmospheric oxygen

This photo shows researchers doing field sampling of a pyrite-rich black shale outcrop in China. The weathering of such sediments, which contain sulfur originally buried from the ocean, transfers sulfur isotope signals to the ocean to be buried again in marine sediments. -  Chu Research Group, Institute of Geology and Geophysics, Chinese Academy of Sciences.
This photo shows researchers doing field sampling of a pyrite-rich black shale outcrop in China. The weathering of such sediments, which contain sulfur originally buried from the ocean, transfers sulfur isotope signals to the ocean to be buried again in marine sediments. – Chu Research Group, Institute of Geology and Geophysics, Chinese Academy of Sciences.

A research team of biogeochemists at the University of California, Riverside has provided a new view on the relationship between the earliest accumulation of oxygen in the atmosphere, arguably the most important biological event in Earth history, and its relationship to the sulfur cycle.

A general consensus exists that appreciable oxygen first accumulated in Earth’s atmosphere around 2.4 to 2.3 billion years ago. Though this paradigm is built upon a wide range of geological and geochemical observations, the famous “smoking gun” for what has come to be known as the “Great Oxidation Event” (GOE) comes from the disappearance of anomalous fractionations in rare sulfur isotopes.

“These isotope fractionations, often referred to as ‘mass-independent fractionations,’ or ‘MIF’ signals, require both the destruction of sulfur dioxide by ultraviolet energy from the sun in an atmosphere without ozone and very low atmospheric oxygen levels in order to be transported and deposited in marine sediments,” said Christopher T. Reinhard, the lead author of the research paper and a former UC Riverside graduate student. “As a result, their presence in ancient rocks is interpreted to reflect vanishingly low atmospheric oxygen levels continuously for the first ~2 billion years of Earth’s history.”

However, diverse types of data are emerging that point to the presence of atmospheric oxygen, and, by inference, the early emergence of oxygenic photosynthesis hundreds of millions of years before these MIF signals disappear from the rock record. These observations motivated Reinhard and colleagues to explore the possible conditions under which inherited MIF signatures may have persisted in the rock record long after oxygen accumulated in the atmosphere.

Using a simple quantitative model describing how sulfur and its isotopes cycle through the Earth’s crust, the researchers discovered that under certain conditions these MIF signatures can persist within the ocean and marine sediments long after O2 increases in the atmosphere. Simply put, the weathering of rocks on the continents can transfer the MIF signal to the oceans and their sediments long after production of this fingerprint has ceased in an oxygenated atmosphere.

“This lag would blur our ability to date the timing of the GOE and would allow for dynamic rising and falling oxygen levels during a protracted transition from an atmosphere without oxygen to one rich in this life-giving gas,” Reinhard said.

Study results appear in Nature‘s advanced online publication on April 24.

Reinhard explained that once MIF signals formed in an oxygen-poor atmosphere are captured in pyrite and other minerals in sedimentary rocks, they are recycled when those rocks are later uplifted as mountain ranges and the pyrite is oxidized.

“Under certain conditions, this will create a sort of ‘memory effect’ of these MIF signatures, providing a decoupling in time between the burial of MIF in sediments and oxygen accumulation at Earth’s surface,” he said.


According to the researchers, the key here is burying a distinct MIF signal in deep sea sediments, which are then subducted and removed from Earth’s surface.

“This would create a complementary signal in minerals that are weathered and delivered to the oceans, something that we actually see evidence of in the rock record,” said Noah Planavsky, the second author of the research paper and a former UC Riverside graduate student now at Caltech. “This signal can then be perpetuated through time without the need to generate it within the atmosphere contemporaneously.”

Reinhard, now a postdoctoral fellow at Caltech and soon to be an assistant professor at Georgia Institute of Technology, explained that although the researchers’ new model provides a plausible mechanism for reconciling recent conflicting data, this can only occur when certain key conditions are met – and these conditions are likely to have changed through time during Earth’s long early history.

“There is obviously much further work to do, but we hope that our model is one step toward a more integrated view of how Earth’s crust, mantle and atmosphere interact in the global sulfur cycle,” he said.

Timothy W. Lyons, a professor of biogeochemistry at UCR and the principal investigator of the research project noted that this is a fundamentally new and potentially very important way of looking at the sulfur isotope record and its relationship to biospheric oxygenation.

“The message is that sulfur isotope records, when viewed through the filter of sedimentary recycling, may challenge efforts to precisely date the GOE and its relationship to early life, while opening the door to the wonderful unknowns we should expect and embrace,” he said.

The Earth’s center is 1,000 degrees hotter than previously thought

Recreating the Earth's liquid iron core in the laboratory: a speck-sized piece of iron is thermally isolated and placed between the tips of two small conical diamonds. Pressing the two diamonds together produces pressures of 2 million atmospheres and more. As a laser beam heats the sample to temperatures of 3000 to 5000 degrees, a thin beam of synchrotron X-rays is used to detect whether it has started to melt. This will change its crystalline structure, in turn modifying the 'diffraction pattern' of deflected X-rays behind the sample. -  ESRF/Denis Andrault.
Recreating the Earth’s liquid iron core in the laboratory: a speck-sized piece of iron is thermally isolated and placed between the tips of two small conical diamonds. Pressing the two diamonds together produces pressures of 2 million atmospheres and more. As a laser beam heats the sample to temperatures of 3000 to 5000 degrees, a thin beam of synchrotron X-rays is used to detect whether it has started to melt. This will change its crystalline structure, in turn modifying the ‘diffraction pattern’ of deflected X-rays behind the sample. – ESRF/Denis Andrault.

Scientists have determined the temperature near the Earth’s center to be 6000 degrees Celsius, 1000 degrees hotter than in a previous experiment run 20 years ago. These measurements confirm geophysical models that the temperature difference between the solid core and the mantle above, must be at least 1500 degrees to explain why the Earth has a magnetic field. The scientists were even able to establish why the earlier experiment had produced a lower temperature figure. The results are published on 26 April 2013 in Science.

The research team was led by Agnès Dewaele from the French national technological research organization CEA, alongside members of the French National Center for Scientific Research CNRS and the European Synchrotron Radiation Facility ESRF in Grenoble (France).

The Earth’s core consists mainly of a sphere of liquid iron at temperatures above 4000 degrees and pressures of more than 1.3 million atmospheres. Under these conditions, iron is as liquid as the water in the oceans. It is only at the very center of the Earth, where pressure and temperature rise even higher, that the liquid iron solidifies. Analysis of earthquake-triggered seismic waves passing through the Earth, tells us the thickness of the solid and liquid cores, and even how the pressure in the Earth increases with depth. However these waves do not provide information on temperature, which has an important influence on the movement of material within the liquid core and the solid mantle above. Indeed the temperature difference between the mantle and the core is the main driver of large-scale thermal movements, which together with the Earth’s rotation, act like a dynamo generating the Earth’s magnetic field. The temperature profile through the Earth’s interior also underpins geophysical models that explain the creation and intense activity of hot-spot volcanoes like the Hawaiian Islands or La Réunion.

To generate an accurate picture of the temperature profile within the Earth’s centre, scientists can look at the melting point of iron at different pressures in the laboratory, using a diamond anvil cell to compress speck-sized samples to pressures of several million atmospheres, and powerful laser beams to heat them to 4000 or even 5000 degrees Celsius.”In practice, many experimental challenges have to be met”, explains Agnès Dewaele from CEA, “as the iron sample has to be insulated thermally and also must not be allowed to chemically react with its environment. Even if a sample reaches the extreme temperatures and pressures at the centre of the Earth, it will only do so for a matter of seconds. In this short timeframe it is extremely difficult to determine whether it has started to melt or is still solid”.

This is where X-rays come into play. “We have developed a new technique where an intense beam of X-rays from the synchrotron can probe a sample and deduce whether it is solid, liquid or partially molten within as little as a second, using a process known diffraction”, says Mohamed Mezouar from the ESRF, “and this is short enough to keep temperature and pressure constant, and at the same time avoid any chemical reactions”.

The scientists determined experimentally the melting point of iron up to 4800 degrees Celsius and 2.2 million atmospheres pressure, and then used an extrapolation method to determine that at 3.3 million atmospheres, the pressure at the border between liquid and solid core, the temperature would be 6000 +/- 500 degrees. This extrapolated value could slightly change if iron undergoes an unknown phase transition between the measured and the extrapolated values.

When the scientists scanned across the area of pressures and temperatures, they observed why Reinhard Boehler, then at the MPI for Chemistry in Mainz (Germany), had in 1993 published values about 1000 degrees lower. Starting at 2400 degrees, recrystallization effects appear on the surface of the iron samples, leading to dynamic changes of the solid iron’s crystalline structure. The experiment twenty years ago used an optical technique to determine whether the samples were solid or molten, and it is highly probable that the observation of recrystallization at the surface was interpreted as melting.

“We are of course very satisfied that our experiment validated today’s best theories on heat transfer from the Earth’s core and the generation of the Earth’s magnetic field. I am hopeful that in the not-so-distant future, we can reproduce in our laboratories, and investigate with synchrotron X-rays, every state of matter inside the Earth,” concludes Agnès Dewaele.

The Earth’s center is 1,000 degrees hotter than previously thought

Recreating the Earth's liquid iron core in the laboratory: a speck-sized piece of iron is thermally isolated and placed between the tips of two small conical diamonds. Pressing the two diamonds together produces pressures of 2 million atmospheres and more. As a laser beam heats the sample to temperatures of 3000 to 5000 degrees, a thin beam of synchrotron X-rays is used to detect whether it has started to melt. This will change its crystalline structure, in turn modifying the 'diffraction pattern' of deflected X-rays behind the sample. -  ESRF/Denis Andrault.
Recreating the Earth’s liquid iron core in the laboratory: a speck-sized piece of iron is thermally isolated and placed between the tips of two small conical diamonds. Pressing the two diamonds together produces pressures of 2 million atmospheres and more. As a laser beam heats the sample to temperatures of 3000 to 5000 degrees, a thin beam of synchrotron X-rays is used to detect whether it has started to melt. This will change its crystalline structure, in turn modifying the ‘diffraction pattern’ of deflected X-rays behind the sample. – ESRF/Denis Andrault.

Scientists have determined the temperature near the Earth’s center to be 6000 degrees Celsius, 1000 degrees hotter than in a previous experiment run 20 years ago. These measurements confirm geophysical models that the temperature difference between the solid core and the mantle above, must be at least 1500 degrees to explain why the Earth has a magnetic field. The scientists were even able to establish why the earlier experiment had produced a lower temperature figure. The results are published on 26 April 2013 in Science.

The research team was led by Agnès Dewaele from the French national technological research organization CEA, alongside members of the French National Center for Scientific Research CNRS and the European Synchrotron Radiation Facility ESRF in Grenoble (France).

The Earth’s core consists mainly of a sphere of liquid iron at temperatures above 4000 degrees and pressures of more than 1.3 million atmospheres. Under these conditions, iron is as liquid as the water in the oceans. It is only at the very center of the Earth, where pressure and temperature rise even higher, that the liquid iron solidifies. Analysis of earthquake-triggered seismic waves passing through the Earth, tells us the thickness of the solid and liquid cores, and even how the pressure in the Earth increases with depth. However these waves do not provide information on temperature, which has an important influence on the movement of material within the liquid core and the solid mantle above. Indeed the temperature difference between the mantle and the core is the main driver of large-scale thermal movements, which together with the Earth’s rotation, act like a dynamo generating the Earth’s magnetic field. The temperature profile through the Earth’s interior also underpins geophysical models that explain the creation and intense activity of hot-spot volcanoes like the Hawaiian Islands or La Réunion.

To generate an accurate picture of the temperature profile within the Earth’s centre, scientists can look at the melting point of iron at different pressures in the laboratory, using a diamond anvil cell to compress speck-sized samples to pressures of several million atmospheres, and powerful laser beams to heat them to 4000 or even 5000 degrees Celsius.”In practice, many experimental challenges have to be met”, explains Agnès Dewaele from CEA, “as the iron sample has to be insulated thermally and also must not be allowed to chemically react with its environment. Even if a sample reaches the extreme temperatures and pressures at the centre of the Earth, it will only do so for a matter of seconds. In this short timeframe it is extremely difficult to determine whether it has started to melt or is still solid”.

This is where X-rays come into play. “We have developed a new technique where an intense beam of X-rays from the synchrotron can probe a sample and deduce whether it is solid, liquid or partially molten within as little as a second, using a process known diffraction”, says Mohamed Mezouar from the ESRF, “and this is short enough to keep temperature and pressure constant, and at the same time avoid any chemical reactions”.

The scientists determined experimentally the melting point of iron up to 4800 degrees Celsius and 2.2 million atmospheres pressure, and then used an extrapolation method to determine that at 3.3 million atmospheres, the pressure at the border between liquid and solid core, the temperature would be 6000 +/- 500 degrees. This extrapolated value could slightly change if iron undergoes an unknown phase transition between the measured and the extrapolated values.

When the scientists scanned across the area of pressures and temperatures, they observed why Reinhard Boehler, then at the MPI for Chemistry in Mainz (Germany), had in 1993 published values about 1000 degrees lower. Starting at 2400 degrees, recrystallization effects appear on the surface of the iron samples, leading to dynamic changes of the solid iron’s crystalline structure. The experiment twenty years ago used an optical technique to determine whether the samples were solid or molten, and it is highly probable that the observation of recrystallization at the surface was interpreted as melting.

“We are of course very satisfied that our experiment validated today’s best theories on heat transfer from the Earth’s core and the generation of the Earth’s magnetic field. I am hopeful that in the not-so-distant future, we can reproduce in our laboratories, and investigate with synchrotron X-rays, every state of matter inside the Earth,” concludes Agnès Dewaele.

Unique chemistry reveals eruption of ancient materials once at Earth’s surface

An international team of researchers, including Scripps Institution of Oceanography, UC San Diego, geochemist James Day, has found new evidence that material contained in oceanic lava flows originated in Earth’s ancient Archean crust. These findings support the theory that much of the Earth’s original crust has been recycled by the process of subduction, helping to explain how the Earth has formed and changed over time.

The Archean geologic eon, Earth’s second oldest, dating from 3.8 to 2.5 billion years ago, is the source of the oldest exposed rock formations on the planet’s surface. (Archean rocks are known from Greenland, the Canadian Shield, the Baltic Shield, Scotland, India, Brazil, western Australia, and southern Africa.) Although the first continents were formed during the Archean eon, rock of this age makes up only around seven percent of the world’s current crust.

“Our new results are important because they provide strong evidence not only to tie materials that were once on Earth’s surface to an entire cycle of subduction, storage in the mantle, and return to the surface as lavas, but they also place a firm time constraint on when plate tectonics began; no later than 2.5 billion years ago,” said Day. “This is because mass independent sulfur signatures have only been shown to occur in the atmosphere during periods of low oxygenation prior to the rise of oxygen-exhaling organisms.”

The new study, which will be published in the April 24 issue of the journal Nature, adds further support to the theory that most of the Archean crust was subducted or folded back into the Earth’s mantle, evidence of which is seen in the presence of specific sulfur isotopes found in some oceanic lava flows.

According to the researchers, because terrestrial independently fractionated (MIF) sulfur-isotope isotope signatures were generated exclusively through atmospheric photochemical reactions until about 2.5 billion years ago, material containing such isotopes must have originated in the Archean crust. In the new study, the researchers found MIF sulfur-isotope signatures in olivine-hosted sulfides from relatively young (20-million-year-old) ocean island basalts (OIB) from Mangaia, Cook Islands (Polynesia), providing evidence that the mantle is the only possible source of the ancient Archean materials found in the Mangaia lavas.

“The discovery of MIF-S isotope in these young oceanic lavas suggests that sulfur-likely derived from the hydrothermally-altered oceanic crust-was subducted into the mantle more than 2.5 billion years ago and recycled into the mantle source of the Mangaia lavas,” said Rita Cabral, the study’s primary author and a graduate student in Boston University’s Department of Earth and Environment.

The data also complement evidence for sulfur recycling of ancient sedimentary materials to the subcontinental lithospheric mantle previously identified in diamond inclusions.

Unique chemistry reveals eruption of ancient materials once at Earth’s surface

An international team of researchers, including Scripps Institution of Oceanography, UC San Diego, geochemist James Day, has found new evidence that material contained in oceanic lava flows originated in Earth’s ancient Archean crust. These findings support the theory that much of the Earth’s original crust has been recycled by the process of subduction, helping to explain how the Earth has formed and changed over time.

The Archean geologic eon, Earth’s second oldest, dating from 3.8 to 2.5 billion years ago, is the source of the oldest exposed rock formations on the planet’s surface. (Archean rocks are known from Greenland, the Canadian Shield, the Baltic Shield, Scotland, India, Brazil, western Australia, and southern Africa.) Although the first continents were formed during the Archean eon, rock of this age makes up only around seven percent of the world’s current crust.

“Our new results are important because they provide strong evidence not only to tie materials that were once on Earth’s surface to an entire cycle of subduction, storage in the mantle, and return to the surface as lavas, but they also place a firm time constraint on when plate tectonics began; no later than 2.5 billion years ago,” said Day. “This is because mass independent sulfur signatures have only been shown to occur in the atmosphere during periods of low oxygenation prior to the rise of oxygen-exhaling organisms.”

The new study, which will be published in the April 24 issue of the journal Nature, adds further support to the theory that most of the Archean crust was subducted or folded back into the Earth’s mantle, evidence of which is seen in the presence of specific sulfur isotopes found in some oceanic lava flows.

According to the researchers, because terrestrial independently fractionated (MIF) sulfur-isotope isotope signatures were generated exclusively through atmospheric photochemical reactions until about 2.5 billion years ago, material containing such isotopes must have originated in the Archean crust. In the new study, the researchers found MIF sulfur-isotope signatures in olivine-hosted sulfides from relatively young (20-million-year-old) ocean island basalts (OIB) from Mangaia, Cook Islands (Polynesia), providing evidence that the mantle is the only possible source of the ancient Archean materials found in the Mangaia lavas.

“The discovery of MIF-S isotope in these young oceanic lavas suggests that sulfur-likely derived from the hydrothermally-altered oceanic crust-was subducted into the mantle more than 2.5 billion years ago and recycled into the mantle source of the Mangaia lavas,” said Rita Cabral, the study’s primary author and a graduate student in Boston University’s Department of Earth and Environment.

The data also complement evidence for sulfur recycling of ancient sedimentary materials to the subcontinental lithospheric mantle previously identified in diamond inclusions.