Scientists observe the Earth grow a new layer under an Icelandic volcano

New research into an Icelandic eruption has shed light on how the Earth’s crust forms, according to a paper published today in Nature.

When the Bárðarbunga volcano, which is buried beneath Iceland’s Vatnajökull ice cap, reawakened in August 2014, scientists had a rare opportunity to monitor how the magma flowed through cracks in the rock away from the volcano. The molten rock forms vertical sheet-like features known as dykes, which force the surrounding rock apart.

Study co-author Professor Andy Hooper from the Centre for Observation and Modelling of Earthquakes, volcanoes and Tectonics (COMET) at the University of Leeds explained: “New crust forms where two tectonic plates are moving away from each other. Mostly this happens beneath the oceans, where it is difficult to observe.

“However, in Iceland this happens beneath dry land. The events leading to the eruption in August 2014 are the first time that such a rifting episode has occurred there and been observed with modern tools, like GPS and satellite radar.”

Although it has a long history of eruptions, Bárðarbunga has been increasingly restless since 2005. There was a particularly dynamic period in August and September this year, when more than 22,000 earthquakes were recorded in or around the volcano in just four weeks, due to stress being released as magma forced its way through the rock.

Using GPS and satellite measurements, the team were able to track the path of the magma for over 45km before it reached a point where it began to erupt, and continues to do so to this day. The rate of dyke propagation was variable and slowed as the magma reached natural barriers, which were overcome by the build-up of pressure, creating a new segment.

The dyke grows in segments, breaking through from one to the next by the build up of pressure. This explains how focused upwelling of magma under central volcanoes is effectively redistributed over large distances to create new upper crust at divergent plate boundaries, the authors conclude.

As well as the dyke, the team found ‘ice cauldrons’ – shallow depressions in the ice with circular crevasses, where the base of the glacier had been melted by magma. In addition, radar measurements showed that the ice inside Bárðarbunga’s crater had sunk by 16m, as the volcano floor collapsed.

COMET PhD student Karsten Spaans from the University of Leeds, a co-author of the study, added: “Using radar measurements from space, we can form an image of caldera movement occurring in one day. Usually we expect to see just noise in the image, but we were amazed to see up to 55cm of subsidence.”

Like other liquids, magma flows along the path of least resistance, which explains why the dyke at Bárðarbunga changed direction as it progressed. Magma flow was influenced mostly by the lie of the land to start with, but as it moved away from the steeper slopes, the influence of plate movements became more important.

Summarising the findings, Professor Hooper said: “Our observations of this event showed that the magma injected into the crust took an incredibly roundabout path and proceeded in fits and starts.

“Initially we were surprised at this complexity, but it turns out we can explain all the twists and turns with a relatively simple model, which considers just the pressure of rock and ice above, and the pull exerted by the plates moving apart.”

The paper ‘Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland’ is published in Nature on 15 December 2014.

The research leading to these results has received funding from the European Community’s Seventh Framework Programme under Grant Agreement No. 308377 (Project FUTUREVOLC)

Scientists observe the Earth grow a new layer under an Icelandic volcano

New research into an Icelandic eruption has shed light on how the Earth’s crust forms, according to a paper published today in Nature.

When the Bárðarbunga volcano, which is buried beneath Iceland’s Vatnajökull ice cap, reawakened in August 2014, scientists had a rare opportunity to monitor how the magma flowed through cracks in the rock away from the volcano. The molten rock forms vertical sheet-like features known as dykes, which force the surrounding rock apart.

Study co-author Professor Andy Hooper from the Centre for Observation and Modelling of Earthquakes, volcanoes and Tectonics (COMET) at the University of Leeds explained: “New crust forms where two tectonic plates are moving away from each other. Mostly this happens beneath the oceans, where it is difficult to observe.

“However, in Iceland this happens beneath dry land. The events leading to the eruption in August 2014 are the first time that such a rifting episode has occurred there and been observed with modern tools, like GPS and satellite radar.”

Although it has a long history of eruptions, Bárðarbunga has been increasingly restless since 2005. There was a particularly dynamic period in August and September this year, when more than 22,000 earthquakes were recorded in or around the volcano in just four weeks, due to stress being released as magma forced its way through the rock.

Using GPS and satellite measurements, the team were able to track the path of the magma for over 45km before it reached a point where it began to erupt, and continues to do so to this day. The rate of dyke propagation was variable and slowed as the magma reached natural barriers, which were overcome by the build-up of pressure, creating a new segment.

The dyke grows in segments, breaking through from one to the next by the build up of pressure. This explains how focused upwelling of magma under central volcanoes is effectively redistributed over large distances to create new upper crust at divergent plate boundaries, the authors conclude.

As well as the dyke, the team found ‘ice cauldrons’ – shallow depressions in the ice with circular crevasses, where the base of the glacier had been melted by magma. In addition, radar measurements showed that the ice inside Bárðarbunga’s crater had sunk by 16m, as the volcano floor collapsed.

COMET PhD student Karsten Spaans from the University of Leeds, a co-author of the study, added: “Using radar measurements from space, we can form an image of caldera movement occurring in one day. Usually we expect to see just noise in the image, but we were amazed to see up to 55cm of subsidence.”

Like other liquids, magma flows along the path of least resistance, which explains why the dyke at Bárðarbunga changed direction as it progressed. Magma flow was influenced mostly by the lie of the land to start with, but as it moved away from the steeper slopes, the influence of plate movements became more important.

Summarising the findings, Professor Hooper said: “Our observations of this event showed that the magma injected into the crust took an incredibly roundabout path and proceeded in fits and starts.

“Initially we were surprised at this complexity, but it turns out we can explain all the twists and turns with a relatively simple model, which considers just the pressure of rock and ice above, and the pull exerted by the plates moving apart.”

The paper ‘Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland’ is published in Nature on 15 December 2014.

The research leading to these results has received funding from the European Community’s Seventh Framework Programme under Grant Agreement No. 308377 (Project FUTUREVOLC)

Geophysicists challenge traditional theory underlying the origin of mid-plate volcanoes

Traditional thought holds that hot updrafts from the Earth's core cause volcanoes, but researchers say eruptions may stem from the asthenosphere, a layer closer to the surface. -  Virginia Tech
Traditional thought holds that hot updrafts from the Earth’s core cause volcanoes, but researchers say eruptions may stem from the asthenosphere, a layer closer to the surface. – Virginia Tech

A long-held assumption about the Earth is discussed in today’s edition of Science, as Don L. Anderson, an emeritus professor with the Seismological Laboratory of the California Institute of Technology, and Scott King, a professor of geophysics in the College of Science at Virginia Tech, look at how a layer beneath the Earth’s crust may be responsible for volcanic eruptions.

The discovery challenges conventional thought that volcanoes are caused when plates that make up the planet’s crust shift and release heat.

Instead of coming from deep within the interior of the planet, the responsibility is closer to the surface, about 80 kilometers to 200 kilometers deep — a layer above the Earth’s mantle, known as the as the asthenosphere.

“For nearly 40 years there has been a debate over a theory that volcanic island chains, such as Hawaii, have been formed by the interaction between plates at the surface and plumes of hot material that rise from the core-mantle boundary nearly 1,800 miles below the Earth’s surface,” King said. “Our paper shows that a hot layer beneath the plates may explain the origin of mid-plate volcanoes without resorting to deep conduits from halfway to the center of the Earth.”

Traditionally, the asthenosphere has been viewed as a passive structure that separates the moving tectonic plates from the mantle.

As tectonic plates move several inches every year, the boundaries between the plates spawn most of the planet’s volcanoes and earthquakes.

“As the Earth cools, the tectonic plates sink and displace warmer material deep within the interior of the Earth,” explained King. “This material rises as two broad, passive updrafts that seismologists have long recognized in their imaging of the interior of the Earth.”

The work of Anderson and King, however, shows that the hot, weak region beneath the plates acts as a lubricating layer, preventing the plates from dragging the material below along with them as they move.

The researchers show this lubricating layer is also the hottest part of the mantle, so there is no need for heat to be carried up to explain mid-plate volcanoes.

“We’re taking the position that plate tectonics and mid-plate volcanoes are the natural results of processes in the plates and the layer beneath them,” King said.

Geophysicists challenge traditional theory underlying the origin of mid-plate volcanoes

Traditional thought holds that hot updrafts from the Earth's core cause volcanoes, but researchers say eruptions may stem from the asthenosphere, a layer closer to the surface. -  Virginia Tech
Traditional thought holds that hot updrafts from the Earth’s core cause volcanoes, but researchers say eruptions may stem from the asthenosphere, a layer closer to the surface. – Virginia Tech

A long-held assumption about the Earth is discussed in today’s edition of Science, as Don L. Anderson, an emeritus professor with the Seismological Laboratory of the California Institute of Technology, and Scott King, a professor of geophysics in the College of Science at Virginia Tech, look at how a layer beneath the Earth’s crust may be responsible for volcanic eruptions.

The discovery challenges conventional thought that volcanoes are caused when plates that make up the planet’s crust shift and release heat.

Instead of coming from deep within the interior of the planet, the responsibility is closer to the surface, about 80 kilometers to 200 kilometers deep — a layer above the Earth’s mantle, known as the as the asthenosphere.

“For nearly 40 years there has been a debate over a theory that volcanic island chains, such as Hawaii, have been formed by the interaction between plates at the surface and plumes of hot material that rise from the core-mantle boundary nearly 1,800 miles below the Earth’s surface,” King said. “Our paper shows that a hot layer beneath the plates may explain the origin of mid-plate volcanoes without resorting to deep conduits from halfway to the center of the Earth.”

Traditionally, the asthenosphere has been viewed as a passive structure that separates the moving tectonic plates from the mantle.

As tectonic plates move several inches every year, the boundaries between the plates spawn most of the planet’s volcanoes and earthquakes.

“As the Earth cools, the tectonic plates sink and displace warmer material deep within the interior of the Earth,” explained King. “This material rises as two broad, passive updrafts that seismologists have long recognized in their imaging of the interior of the Earth.”

The work of Anderson and King, however, shows that the hot, weak region beneath the plates acts as a lubricating layer, preventing the plates from dragging the material below along with them as they move.

The researchers show this lubricating layer is also the hottest part of the mantle, so there is no need for heat to be carried up to explain mid-plate volcanoes.

“We’re taking the position that plate tectonics and mid-plate volcanoes are the natural results of processes in the plates and the layer beneath them,” King said.

UW team explores large, restless volcanic field in Chile

If Brad Singer knew for sure what was happening three miles under an odd-shaped lake in the Andes, he might be less eager to spend a good part of his career investigating a volcanic field that has erupted 36 times during the last 25,000 years. As he leads a large scientific team exploring a region in the Andes called Laguna del Maule, Singer hopes the area remains quiet.

But the primary reason to expend so much effort on this area boils down to one fact: The rate of uplift is among the highest ever observed by satellite measurement for a volcano that is not actively erupting.

That uplift is almost definitely due to a large intrusion of magma — molten rock — beneath the volcanic complex. For seven years, an area larger than the city of Madison has been rising by 10 inches per year.

That rapid rise provides a major scientific opportunity: to explore a mega-volcano before it erupts. That effort, and the hazard posed by the restless magma reservoir beneath Laguna del Maule, are described in a major research article in the December issue of the Geological Society of America’s GSA Today.

“We’ve always been looking at these mega-eruptions in the rear-view mirror,” says Singer. “We look at the lava, dust and ash, and try to understand what happened before the eruption. Since these huge eruptions are rare, that’s usually our only option. But we look at the steady uplift at Laguna del Maule, which has a history of regular eruptions, combined with changes in gravity, electrical conductivity and swarms of earthquakes, and we suspect that conditions necessary to trigger another eruption are gathering force.”

Laguna del Maule looks nothing like a classic, cone-shaped volcano, since the high-intensity erosion caused by heavy rain and snow has carried most of the evidence to the nearby Pacific Ocean. But the overpowering reason for the absence of “typical volcano cones” is the nature of the molten rock underground. It’s called rhyolite, and it’s the most explosive type of magma on the planet.

The eruption of a rhyolite volcano is too quick and violent to build up a cone. Instead, this viscous, water-rich magma often explodes into vast quantities of ash that can form deposits hundreds of yards deep, followed by a slower flow of glassy magma that can be tens of yards tall and measure more than a mile in length.

The next eruption could be in the size range of Mount St. Helens — or it could be vastly bigger, Singer says. “We know that over the past million years or so, several eruptions at Laguna del Maule or nearby volcanoes have been more than 100 times larger than Mount St. Helens,” he says. “Those are rare, but they are possible.” Such a mega-eruption could change the weather, disrupt the ecosystem and damage the economy.

Trying to anticipate what Laguna del Maule holds in store, Singer is heading a new $3 million, five-year effort sponsored by the National Science Foundation to document its behavior before an eruption. With colleagues from Chile, Argentina, Canada, Singapore, and Cornell and Georgia Tech universities, he is masterminding an effort to build a scientific model of the underground forces that could lead to eruption. “This model should capture how this system has evolved in the crust at all scales, from the microscopic to basinwide, over the last 100,000 years,” Singer says. “It’s like a movie from the past to the present and into the future.”

Over the next five years, Singer says he and 30 colleagues will “throw everything, including the kitchen sink, at the problem — geology, geochemistry, geochronology and geophysics — to help measure, and then model, what’s going on.”

One key source of information on volcanoes is seismic waves. Ground shaking triggered by the movement of magma can signal an impending eruption. Team member Clifford Thurber, a seismologist and professor of geoscience at UW-Madison, wants to use distant earthquakes to locate the underground magma body.

As many as 50 seismometers will eventually be emplaced above and around the magma at Laguna del Maule, in the effort to create a 3-D image of Earth’s crust in the area.

By tracking multiple earthquakes over several years, Thurber and his colleagues want to pinpoint the size and location of the magma body — roughly estimated as an oval measuring five kilometers (3.1 miles) by 10 kilometers (6.2 miles).

Each seismometer will record the travel time of earthquake waves originating within a few thousand kilometers, Thurber explains. Since soft rock transmits sound less efficiently than hard rock, “we expect that waves that pass through the presumed magma body will be delayed,” Thurber says. “It’s very simple. It’s like a CT scan, except instead of density we are looking at seismic wave velocity.”

As Singer, who has been visiting Laguna del Maule since 1998, notes, “The rate of uplift — among the highest ever observed — has been sustained for seven years, and we have discovered a large, fluid-rich zone in the crust under the lake using electrical resistivity methods. Thus, there are not many possible explanations other than a big, active body of magma at a shallow depth.”

The expanding body of magma could freeze in place — or blow its top, he says. “One thing we know for sure is that the surface cannot continue rising indefinitely.”

UW team explores large, restless volcanic field in Chile

If Brad Singer knew for sure what was happening three miles under an odd-shaped lake in the Andes, he might be less eager to spend a good part of his career investigating a volcanic field that has erupted 36 times during the last 25,000 years. As he leads a large scientific team exploring a region in the Andes called Laguna del Maule, Singer hopes the area remains quiet.

But the primary reason to expend so much effort on this area boils down to one fact: The rate of uplift is among the highest ever observed by satellite measurement for a volcano that is not actively erupting.

That uplift is almost definitely due to a large intrusion of magma — molten rock — beneath the volcanic complex. For seven years, an area larger than the city of Madison has been rising by 10 inches per year.

That rapid rise provides a major scientific opportunity: to explore a mega-volcano before it erupts. That effort, and the hazard posed by the restless magma reservoir beneath Laguna del Maule, are described in a major research article in the December issue of the Geological Society of America’s GSA Today.

“We’ve always been looking at these mega-eruptions in the rear-view mirror,” says Singer. “We look at the lava, dust and ash, and try to understand what happened before the eruption. Since these huge eruptions are rare, that’s usually our only option. But we look at the steady uplift at Laguna del Maule, which has a history of regular eruptions, combined with changes in gravity, electrical conductivity and swarms of earthquakes, and we suspect that conditions necessary to trigger another eruption are gathering force.”

Laguna del Maule looks nothing like a classic, cone-shaped volcano, since the high-intensity erosion caused by heavy rain and snow has carried most of the evidence to the nearby Pacific Ocean. But the overpowering reason for the absence of “typical volcano cones” is the nature of the molten rock underground. It’s called rhyolite, and it’s the most explosive type of magma on the planet.

The eruption of a rhyolite volcano is too quick and violent to build up a cone. Instead, this viscous, water-rich magma often explodes into vast quantities of ash that can form deposits hundreds of yards deep, followed by a slower flow of glassy magma that can be tens of yards tall and measure more than a mile in length.

The next eruption could be in the size range of Mount St. Helens — or it could be vastly bigger, Singer says. “We know that over the past million years or so, several eruptions at Laguna del Maule or nearby volcanoes have been more than 100 times larger than Mount St. Helens,” he says. “Those are rare, but they are possible.” Such a mega-eruption could change the weather, disrupt the ecosystem and damage the economy.

Trying to anticipate what Laguna del Maule holds in store, Singer is heading a new $3 million, five-year effort sponsored by the National Science Foundation to document its behavior before an eruption. With colleagues from Chile, Argentina, Canada, Singapore, and Cornell and Georgia Tech universities, he is masterminding an effort to build a scientific model of the underground forces that could lead to eruption. “This model should capture how this system has evolved in the crust at all scales, from the microscopic to basinwide, over the last 100,000 years,” Singer says. “It’s like a movie from the past to the present and into the future.”

Over the next five years, Singer says he and 30 colleagues will “throw everything, including the kitchen sink, at the problem — geology, geochemistry, geochronology and geophysics — to help measure, and then model, what’s going on.”

One key source of information on volcanoes is seismic waves. Ground shaking triggered by the movement of magma can signal an impending eruption. Team member Clifford Thurber, a seismologist and professor of geoscience at UW-Madison, wants to use distant earthquakes to locate the underground magma body.

As many as 50 seismometers will eventually be emplaced above and around the magma at Laguna del Maule, in the effort to create a 3-D image of Earth’s crust in the area.

By tracking multiple earthquakes over several years, Thurber and his colleagues want to pinpoint the size and location of the magma body — roughly estimated as an oval measuring five kilometers (3.1 miles) by 10 kilometers (6.2 miles).

Each seismometer will record the travel time of earthquake waves originating within a few thousand kilometers, Thurber explains. Since soft rock transmits sound less efficiently than hard rock, “we expect that waves that pass through the presumed magma body will be delayed,” Thurber says. “It’s very simple. It’s like a CT scan, except instead of density we are looking at seismic wave velocity.”

As Singer, who has been visiting Laguna del Maule since 1998, notes, “The rate of uplift — among the highest ever observed — has been sustained for seven years, and we have discovered a large, fluid-rich zone in the crust under the lake using electrical resistivity methods. Thus, there are not many possible explanations other than a big, active body of magma at a shallow depth.”

The expanding body of magma could freeze in place — or blow its top, he says. “One thing we know for sure is that the surface cannot continue rising indefinitely.”

Magma pancakes beneath Lake Toba

The tremendous amounts of lava that are emitted during super-eruptions accumulate over millions of years prior to the event in the Earth’s crust. These reservoirs consist of magma that intrudes into the crust in the form of numerous horizontally oriented sheets resting on top of each other like a pile of pancakes.

A team of geoscientists from Novosibirsk, Paris and Potsdam presents these results in the current issue of Science (2014/10/31). The scientists investigate the question on where the tremendous amounts of material that are ejected to from huge calderas during super-eruptions actually originate. Here we are not dealing with large volcanic eruptions of the size of Pinatubo of Mount St. Helens, here we are talking about extreme events: The Toba-caldera in the Sumatra subduction zone in Indonesia originated from one of the largest volcanic eruption in recent Earth history, about 74,000 years ago. It emitted the enormous amount of 2,800 cubic kilometers of volcanic material with a dramatic global impact on climate and environment. Hereby, the 80 km long Lake Toba was formed.

Geoscientists were interested in finding out: How can the gigantic amounts of eruptible material required to form such a super volcano accumulate in the Earth’s crust. Was this a singular event thousands of years ago or can it happen again?

Researchers from the GFZ German Research Centre for Geosciences successfully installed a seismometer network in the Toba area to investigate these questions and provided the data to all participating scientists via the GEOFON data archive. GFZ scientist, Christoph Sens-Schönfelder, a co-author of the study explains: “With a new seismological method we were able to investigate the internal structure of the magma reservoir beneath the Toba-caldera. We found that the middle crust below the Toba supervolcano is horizontally layered.” The answer thus lies in the structure of the magma reservoir. Here, below 7 kilometers the crust consists of many, mostly horizontal, magmatic intrusions still containing molten material.

New seismological technique

It was already suspected that the large volume of magma ejected during the supervolcanic eruption had slowly accumulated over the last few millions of years in the form of consequently emplaced intrusions. This could now be confirmed with the results of field measurements. The GFZ scientists used a novel seismological method for this purpose. Over a six-month period they recorded the ambient seismic noise, the natural vibrations which usually are regarded as disturbing signals. With a statistical approach they analyzed the data and discovered that the velocity of seismic waves beneath Toba depends on the direction in which the waves shear the Earth’s crust. Above 7 kilometers depth the deposits of the last eruption formed a zone of low velocities. Below this depth the seismic anisotropy is caused by horizontally layered intrusions that structure the reservoir like a pile of pancakes. This is reflected in the seismic data.

Supervolcanoes

Not only in Indonesia, but also in other parts of the world there are such supervoclcanoes, which erupt only every couple of hundred thousand years but then in gigantic eruptions. Because of their size those volcanoes do not build up mountains but manifest themselves with their huge carter formed during the eruption – the caldera. Other known supervolcanoes include the area of the Yellow-Stone-Park, volcanoes in the Andes, and the caldera of Lake-Taupo in New Zealand. The present study helps to better understand the processes that lead to such super-eruptions.

Magma pancakes beneath Lake Toba

The tremendous amounts of lava that are emitted during super-eruptions accumulate over millions of years prior to the event in the Earth’s crust. These reservoirs consist of magma that intrudes into the crust in the form of numerous horizontally oriented sheets resting on top of each other like a pile of pancakes.

A team of geoscientists from Novosibirsk, Paris and Potsdam presents these results in the current issue of Science (2014/10/31). The scientists investigate the question on where the tremendous amounts of material that are ejected to from huge calderas during super-eruptions actually originate. Here we are not dealing with large volcanic eruptions of the size of Pinatubo of Mount St. Helens, here we are talking about extreme events: The Toba-caldera in the Sumatra subduction zone in Indonesia originated from one of the largest volcanic eruption in recent Earth history, about 74,000 years ago. It emitted the enormous amount of 2,800 cubic kilometers of volcanic material with a dramatic global impact on climate and environment. Hereby, the 80 km long Lake Toba was formed.

Geoscientists were interested in finding out: How can the gigantic amounts of eruptible material required to form such a super volcano accumulate in the Earth’s crust. Was this a singular event thousands of years ago or can it happen again?

Researchers from the GFZ German Research Centre for Geosciences successfully installed a seismometer network in the Toba area to investigate these questions and provided the data to all participating scientists via the GEOFON data archive. GFZ scientist, Christoph Sens-Schönfelder, a co-author of the study explains: “With a new seismological method we were able to investigate the internal structure of the magma reservoir beneath the Toba-caldera. We found that the middle crust below the Toba supervolcano is horizontally layered.” The answer thus lies in the structure of the magma reservoir. Here, below 7 kilometers the crust consists of many, mostly horizontal, magmatic intrusions still containing molten material.

New seismological technique

It was already suspected that the large volume of magma ejected during the supervolcanic eruption had slowly accumulated over the last few millions of years in the form of consequently emplaced intrusions. This could now be confirmed with the results of field measurements. The GFZ scientists used a novel seismological method for this purpose. Over a six-month period they recorded the ambient seismic noise, the natural vibrations which usually are regarded as disturbing signals. With a statistical approach they analyzed the data and discovered that the velocity of seismic waves beneath Toba depends on the direction in which the waves shear the Earth’s crust. Above 7 kilometers depth the deposits of the last eruption formed a zone of low velocities. Below this depth the seismic anisotropy is caused by horizontally layered intrusions that structure the reservoir like a pile of pancakes. This is reflected in the seismic data.

Supervolcanoes

Not only in Indonesia, but also in other parts of the world there are such supervoclcanoes, which erupt only every couple of hundred thousand years but then in gigantic eruptions. Because of their size those volcanoes do not build up mountains but manifest themselves with their huge carter formed during the eruption – the caldera. Other known supervolcanoes include the area of the Yellow-Stone-Park, volcanoes in the Andes, and the caldera of Lake-Taupo in New Zealand. The present study helps to better understand the processes that lead to such super-eruptions.

Rare 2.5-billion-year-old rocks reveal hot spot of sulfur-breathing bacteria

Gold miners prospecting in a mountainous region of Brazil drilled this 590-foot cylinder of bedrock from the Neoarchaean Eon, which provides rare evidence of conditions on Earth 2.5 billion years ago. -  Alan J. Kaufman
Gold miners prospecting in a mountainous region of Brazil drilled this 590-foot cylinder of bedrock from the Neoarchaean Eon, which provides rare evidence of conditions on Earth 2.5 billion years ago. – Alan J. Kaufman

Wriggle your toes in a marsh’s mucky bottom sediment and you’ll probably inhale a rotten egg smell, the distinctive odor of hydrogen sulfide gas. That’s the biochemical signature of sulfur-using bacteria, one of Earth’s most ancient and widespread life forms.

Among scientists who study the early history of our 4.5 billion-year-old planet, there is a vigorous debate about the evolution of sulfur-dependent bacteria. These simple organisms arose at a time when oxygen levels in the atmosphere were less than one-thousandth of what they are now. Living in ocean waters, they respired (or breathed in) sulfate, a form of sulfur, instead of oxygen. But how did that sulfate reach the ocean, and when did it become abundant enough for living things to use it?

New research by University of Maryland geology doctoral student Iadviga Zhelezinskaia offers a surprising answer. Zhelezinskaia is the first researcher to analyze the biochemical signals of sulfur compounds found in 2.5 billion-year-old carbonate rocks from Brazil. The rocks were formed on the ocean floor in a geologic time known as the Neoarchaean Eon. They surfaced when prospectors drilling for gold in Brazil punched a hole into bedrock and pulled out a 590-foot-long core of ancient rocks.

In research published Nov. 7, 2014 in the journal Science, Zhelezinskaia and three co-authors–physicist John Cliff of the University of Western Australia and geologists Alan Kaufman and James Farquhar of UMD–show that bacteria dependent on sulfate were plentiful in some parts of the Neoarchaean ocean, even though sea water typically contained about 1,000 times less sulfate than it does today.

“The samples Iadviga measured carry a very strong signal that sulfur compounds were consumed and altered by living organisms, which was surprising,” says Farquhar. “She also used basic geochemical models to give an idea of how much sulfate was in the oceans, and finds the sulfate concentrations are very low, much lower than previously thought.”

Geologists study sulfur because it is abundant and combines readily with other elements, forming compounds stable enough to be preserved in the geologic record. Sulfur has four naturally occurring stable isotopes–atomic signatures left in the rock record that scientists can use to identify the elements’ different forms. Researchers measuring sulfur isotope ratios in a rock sample can learn whether the sulfur came from the atmosphere, weathering rocks or biological processes. From that information about the sulfur sources, they can deduce important information about the state of the atmosphere, oceans, continents and biosphere when those rocks formed.

Farquhar and other researchers have used sulfur isotope ratios in Neoarchaean rocks to show that soon after this period, Earth’s atmosphere changed. Oxygen levels soared from just a few parts per million to almost their current level, which is around 21 percent of all the gases in the atmosphere. The Brazilian rocks Zhelezinskaia sampled show only trace amounts of oxygen, a sign they were formed before this atmospheric change.

With very little oxygen, the Neoarchaean Earth was a forbidding place for most modern life forms. The continents were probably much drier and dominated by volcanoes that released sulfur dioxide, carbon dioxide, methane and other greenhouse gases. Temperatures probably ranged between 0 and 100 degrees Celsius (32 to 212 degrees Fahrenheit), warm enough for liquid oceans to form and microbes to grow in them.

Rocks 2.5 billion years old or older are extremely rare, so geologists’ understanding of the Neoarchaean are based on a handful of samples from a few small areas, such as Western Australia, South Africa and Brazil. Geologists theorize that Western Australia and South Africa were once part of an ancient supercontinent called Vaalbara. The Brazilian rock samples are comparable in age, but they may not be from the same supercontinent, Zhelezinskaia says.

Most of the Neoarchaean rocks studied are from Western Australia and South Africa and are black shale, which forms when fine dust settles on the sea floor. The Brazilian prospector’s core contains plenty of black shale and a band of carbonate rock, formed below the surface of shallow seas, in a setting that probably resembled today’s Bahama Islands. Black shale usually contains sulfur-bearing pyrite, but carbonate rock typically does not, so geologists have not focused on sulfur signals in Neoarchaean carbonate rocks until now.

Zhelezinskaia “chose to look at a type of rock that others generally avoided, and what she saw was spectacularly different,” said Kaufman. “It really opened our eyes to the implications of this study.”

The Brazilian carbonate rocks’ isotopic ratios showed they formed in ancient seabed containing sulfate from atmospheric sources, not continental rock. And the isotopic ratios also showed that Neoarchaean bacteria were plentiful in the sediment, respiring sulfate and emitted hydrogen sulfide–the same process that goes on today as bacteria recycle decaying organic matter into minerals and gases.

How could the sulfur-dependent bacteria have thrived during a geologic time when sulfur levels were so low? “It seems that they were in shallow water, where evaporation may have been high enough to concentrate the sulfate, and that would make it abundant enough to support the bacteria,” says Zhelezinskaia.

Zhelezinskaia is now analyzing carbonate rocks of the same age from Western Australia and South Africa, to see if the pattern holds true for rocks formed in other shallow water environments. If it does, the results may change scientists’ understanding of one of Earth’s earliest biological processes.

“There is an ongoing debate about when sulfate-reducing bacteria arose and how that fits into the evolution of life on our planet,” says Farquhar. “These rocks are telling us the bacteria were there 2.5 billion years ago, and they were doing something significant enough that we can see them today.”

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This research was supported by the Fulbright Program (Grantee ID 15110620), the NASA Astrobiology Institute (Grant No. NNA09DA81A) and the National Science Foundation Frontiers in Earth-System Dynamics program (Grant No. 432129). The content of this article does not necessarily reflect the views of these organizations.

“Large sulfur isotope fractionations associated with Neoarchaean microbial sulfate reductions,” Iadviga Zhelezinskaia, Alan J. Kaufman, James Farquhar and John Cliff, was published Nov. 7, 2014 in Science. Download the abstract after 2 p.m. U.S. Eastern time, Nov. 6, 2014: http://www.sciencemag.org/lookup/doi/10.1126/science.1256211

James Farquhar home page

http://www.geol.umd.edu/directory.php?id=13

Alan J. Kaufman home page

http://www.geol.umd.edu/directory.php?id=15

Iadviga Zhelezinskaia home page

http://www.geol.umd.edu/directory.php?id=66

Media Relations Contact: Abby Robinson, 301-405-5845, abbyr@umd.edu

Writer: Heather Dewar

Rare 2.5-billion-year-old rocks reveal hot spot of sulfur-breathing bacteria

Gold miners prospecting in a mountainous region of Brazil drilled this 590-foot cylinder of bedrock from the Neoarchaean Eon, which provides rare evidence of conditions on Earth 2.5 billion years ago. -  Alan J. Kaufman
Gold miners prospecting in a mountainous region of Brazil drilled this 590-foot cylinder of bedrock from the Neoarchaean Eon, which provides rare evidence of conditions on Earth 2.5 billion years ago. – Alan J. Kaufman

Wriggle your toes in a marsh’s mucky bottom sediment and you’ll probably inhale a rotten egg smell, the distinctive odor of hydrogen sulfide gas. That’s the biochemical signature of sulfur-using bacteria, one of Earth’s most ancient and widespread life forms.

Among scientists who study the early history of our 4.5 billion-year-old planet, there is a vigorous debate about the evolution of sulfur-dependent bacteria. These simple organisms arose at a time when oxygen levels in the atmosphere were less than one-thousandth of what they are now. Living in ocean waters, they respired (or breathed in) sulfate, a form of sulfur, instead of oxygen. But how did that sulfate reach the ocean, and when did it become abundant enough for living things to use it?

New research by University of Maryland geology doctoral student Iadviga Zhelezinskaia offers a surprising answer. Zhelezinskaia is the first researcher to analyze the biochemical signals of sulfur compounds found in 2.5 billion-year-old carbonate rocks from Brazil. The rocks were formed on the ocean floor in a geologic time known as the Neoarchaean Eon. They surfaced when prospectors drilling for gold in Brazil punched a hole into bedrock and pulled out a 590-foot-long core of ancient rocks.

In research published Nov. 7, 2014 in the journal Science, Zhelezinskaia and three co-authors–physicist John Cliff of the University of Western Australia and geologists Alan Kaufman and James Farquhar of UMD–show that bacteria dependent on sulfate were plentiful in some parts of the Neoarchaean ocean, even though sea water typically contained about 1,000 times less sulfate than it does today.

“The samples Iadviga measured carry a very strong signal that sulfur compounds were consumed and altered by living organisms, which was surprising,” says Farquhar. “She also used basic geochemical models to give an idea of how much sulfate was in the oceans, and finds the sulfate concentrations are very low, much lower than previously thought.”

Geologists study sulfur because it is abundant and combines readily with other elements, forming compounds stable enough to be preserved in the geologic record. Sulfur has four naturally occurring stable isotopes–atomic signatures left in the rock record that scientists can use to identify the elements’ different forms. Researchers measuring sulfur isotope ratios in a rock sample can learn whether the sulfur came from the atmosphere, weathering rocks or biological processes. From that information about the sulfur sources, they can deduce important information about the state of the atmosphere, oceans, continents and biosphere when those rocks formed.

Farquhar and other researchers have used sulfur isotope ratios in Neoarchaean rocks to show that soon after this period, Earth’s atmosphere changed. Oxygen levels soared from just a few parts per million to almost their current level, which is around 21 percent of all the gases in the atmosphere. The Brazilian rocks Zhelezinskaia sampled show only trace amounts of oxygen, a sign they were formed before this atmospheric change.

With very little oxygen, the Neoarchaean Earth was a forbidding place for most modern life forms. The continents were probably much drier and dominated by volcanoes that released sulfur dioxide, carbon dioxide, methane and other greenhouse gases. Temperatures probably ranged between 0 and 100 degrees Celsius (32 to 212 degrees Fahrenheit), warm enough for liquid oceans to form and microbes to grow in them.

Rocks 2.5 billion years old or older are extremely rare, so geologists’ understanding of the Neoarchaean are based on a handful of samples from a few small areas, such as Western Australia, South Africa and Brazil. Geologists theorize that Western Australia and South Africa were once part of an ancient supercontinent called Vaalbara. The Brazilian rock samples are comparable in age, but they may not be from the same supercontinent, Zhelezinskaia says.

Most of the Neoarchaean rocks studied are from Western Australia and South Africa and are black shale, which forms when fine dust settles on the sea floor. The Brazilian prospector’s core contains plenty of black shale and a band of carbonate rock, formed below the surface of shallow seas, in a setting that probably resembled today’s Bahama Islands. Black shale usually contains sulfur-bearing pyrite, but carbonate rock typically does not, so geologists have not focused on sulfur signals in Neoarchaean carbonate rocks until now.

Zhelezinskaia “chose to look at a type of rock that others generally avoided, and what she saw was spectacularly different,” said Kaufman. “It really opened our eyes to the implications of this study.”

The Brazilian carbonate rocks’ isotopic ratios showed they formed in ancient seabed containing sulfate from atmospheric sources, not continental rock. And the isotopic ratios also showed that Neoarchaean bacteria were plentiful in the sediment, respiring sulfate and emitted hydrogen sulfide–the same process that goes on today as bacteria recycle decaying organic matter into minerals and gases.

How could the sulfur-dependent bacteria have thrived during a geologic time when sulfur levels were so low? “It seems that they were in shallow water, where evaporation may have been high enough to concentrate the sulfate, and that would make it abundant enough to support the bacteria,” says Zhelezinskaia.

Zhelezinskaia is now analyzing carbonate rocks of the same age from Western Australia and South Africa, to see if the pattern holds true for rocks formed in other shallow water environments. If it does, the results may change scientists’ understanding of one of Earth’s earliest biological processes.

“There is an ongoing debate about when sulfate-reducing bacteria arose and how that fits into the evolution of life on our planet,” says Farquhar. “These rocks are telling us the bacteria were there 2.5 billion years ago, and they were doing something significant enough that we can see them today.”

###

This research was supported by the Fulbright Program (Grantee ID 15110620), the NASA Astrobiology Institute (Grant No. NNA09DA81A) and the National Science Foundation Frontiers in Earth-System Dynamics program (Grant No. 432129). The content of this article does not necessarily reflect the views of these organizations.

“Large sulfur isotope fractionations associated with Neoarchaean microbial sulfate reductions,” Iadviga Zhelezinskaia, Alan J. Kaufman, James Farquhar and John Cliff, was published Nov. 7, 2014 in Science. Download the abstract after 2 p.m. U.S. Eastern time, Nov. 6, 2014: http://www.sciencemag.org/lookup/doi/10.1126/science.1256211

James Farquhar home page

http://www.geol.umd.edu/directory.php?id=13

Alan J. Kaufman home page

http://www.geol.umd.edu/directory.php?id=15

Iadviga Zhelezinskaia home page

http://www.geol.umd.edu/directory.php?id=66

Media Relations Contact: Abby Robinson, 301-405-5845, abbyr@umd.edu

Writer: Heather Dewar