River deep, mountain high — new study reveals clues to lifecycle of worlds iconic mountains

This image shows the very steep topography of East Timor. The evolution of this mountain range is dominated by ongoing feedbacks between landslides and river erosion. -  Mike Sandiford University of Melbourne
This image shows the very steep topography of East Timor. The evolution of this mountain range is dominated by ongoing feedbacks between landslides and river erosion. – Mike Sandiford University of Melbourne

Scientists have discovered the reasons behind the lifespan of some of the world’s iconic mountain ranges.

The study conducted by the University of Melbourne, Australia, and Aarhus University, Denmark, has revealed that interactions between landslides and erosion, caused by rivers, explains why some mountain ranges exceed their expected lifespan.

Co-author Professor Mike Sandiford of the School of Earth Sciences at the University of Melbourne said the study had answered the quandary as to why there was fast erosion in active mountain ranges in the Himalayas and slow erosion in others such as the Great Dividing Range in Australia or the Urals in Russia.

“We have shown that links between landslides and rivers are important in maintaining erosion in active or ancient mountain ranges,” he said.

“This study is a great insight into the origins and topography of our globe’s mountainous landscape.”

Mountain ranges are expected to erode away in the absence of tectonic activity but several ranges, such as the Appalachians in the US and the Urals in Russia, have been preserved over several hundred million years.

Co-author, Professor David Egholm from Aarhus University said the new model study published in Nature today provided a plausible mechanism for the preservation of tectonically inactive mountain ranges.

“Computational simulations performed for the study revealed that variations in mountain erosion may relate to a coupling between river incision and landslides,” he said.

Researchers said rivers can cut through bedrock and this process is thought to be the major factor in controlling mountain erosion, however, the long-term preservation of some mountains is at odds with some of the underlying assumptions regarding river erosion rates in current models of river-based landscape evolution.

The study revealed landslides affected river erosion rates in two ways. Large landslides overwhelm river transport capacity and can protect the riverbed from further erosion; conversely, landslides also deliver abrasive agents to the streams, thereby accelerating erosion.

Feedback between these processes can help to stabilize the rates of erosion and increase the lifespan of mountains, the authors said.

A stepping-stone for oxygen on Earth

For most terrestrial life on Earth, oxygen is necessary for survival. But the planet’s atmosphere did not always contain this life-sustaining substance, and one of science’s greatest mysteries is how and when oxygenic photosynthesis-the process responsible for producing oxygen on Earth through the splitting of water molecules-first began. Now, a team led by geobiologists at the California Institute of Technology (Caltech) has found evidence of a precursor photosystem involving manganese that predates cyanobacteria, the first group of organisms to release oxygen into the environment via photosynthesis.

The findings, outlined in the June 24 early edition of the Proceedings of the National Academy of Sciences (PNAS), strongly support the idea that manganese oxidation-which, despite the name, is a chemical reaction that does not have to involve oxygen-provided an evolutionary stepping-stone for the development of water-oxidizing photosynthesis in cyanobacteria.

“Water-oxidizing or water-splitting photosynthesis was invented by cyanobacteria approximately 2.4 billion years ago and then borrowed by other groups of organisms thereafter,” explains Woodward Fischer, assistant professor of geobiology at Caltech and a coauthor of the study. “Algae borrowed this photosynthetic system from cyanobacteria, and plants are just a group of algae that took photosynthesis on land, so we think with this finding we’re looking at the inception of the molecular machinery that would give rise to oxygen.”

Photosynthesis is the process by which energy from the sun is used by plants and other organisms to split water and carbon dioxide molecules to make carbohydrates and oxygen. Manganese is required for water splitting to work, so when scientists began to wonder what evolutionary steps may have led up to an oxygenated atmosphere on Earth, they started to look for evidence of manganese-oxidizing photosynthesis prior to cyanobacteria. Since oxidation simply involves the transfer of electrons to increase the charge on an atom-and this can be accomplished using light or O2-it could have occurred before the rise of oxygen on this planet.

“Manganese plays an essential role in modern biological water splitting as a necessary catalyst in the process, so manganese-oxidizing photosynthesis makes sense as a potential transitional photosystem,” says Jena Johnson, a graduate student in Fischer’s laboratory at Caltech and lead author of the study.

To test the hypothesis that manganese-based photosynthesis occurred prior to the evolution of oxygenic cyanobacteria, the researchers examined drill cores (newly obtained by the Agouron Institute) from 2.415 billion-year-old South African marine sedimentary rocks with large deposits of manganese.

Manganese is soluble in seawater. Indeed, if there are no strong oxidants around to accept electrons from the manganese, it will remain aqueous, Fischer explains, but the second it is oxidized, or loses electrons, manganese precipitates, forming a solid that can become concentrated within seafloor sediments.

“Just the observation of these large enrichments-16 percent manganese in some samples-provided a strong implication that the manganese had been oxidized, but this required confirmation,” he says.

To prove that the manganese was originally part of the South African rock and not deposited there later by hydrothermal fluids or some other phenomena, Johnson and colleagues developed and employed techniques that allowed the team to assess the abundance and oxidation state of manganese-bearing minerals at a very tiny scale of 2 microns.

“And it’s warranted-these rocks are complicated at a micron scale!” Fischer says. “And yet, the rocks occupy hundreds of meters of stratigraphy across hundreds of square kilometers of ocean basin, so you need to be able to work between many scales-very detailed ones, but also across the whole deposit to understand the ancient environmental processes at work.”

Using these multiscale approaches, Johnson and colleagues demonstrated that the manganese was original to the rocks and first deposited in sediments as manganese oxides, and that manganese oxidation occurred over a broad swath of the ancient marine basin during the entire timescale captured by the drill cores.

“It’s really amazing to be able to use X-ray techniques to look back into the rock record and use the chemical observations on the microscale to shed light on some of the fundamental processes and mechanisms that occurred billions of years ago,” says Samuel Webb, coauthor on the paper and beam line scientist at the SLAC National Accelerator Laboratory at Stanford University, where many of the study’s experiments took place. “Questions regarding the evolution of the photosynthetic pathway and the subsequent rise of oxygen in the atmosphere are critical for understanding not only the history of our own planet, but also the basics of how biology has perfected the process of photosynthesis.”

Once the team confirmed that the manganese had been deposited as an oxide phase when the rock was first forming, they checked to see if these manganese oxides were actually formed before water-splitting photosynthesis or if they formed after as a result of reactions with oxygen. They used two different techniques to check whether oxygen was present. It was not-proving that water-splitting photosynthesis had not yet evolved at that point in time. The manganese in the deposits had indeed been oxidized and deposited before the appearance of water-splitting cyanobacteria. This implies, the researchers say, that manganese-oxidizing photosynthesis was a stepping-stone for oxygen-producing, water-splitting photosynthesis.

“I think that there will be a number of additional experiments that people will now attempt to try and reverse engineer a manganese photosynthetic photosystem or cell,” Fischer says. “Once you know that this happened, it all of a sudden gives you reason to take more seriously an experimental program aimed at asking, ‘Can we make a photosystem that’s able to oxidize manganese but doesn’t then go on to split water? How does it behave, and what is its chemistry?’ Even though we know what modern water splitting is and what it looks like, we still don’t know exactly how it works. There is a still a major discovery to be made to find out exactly how the catalysis works, and now knowing where this machinery comes from may open new perspectives into its function-an understanding that could help target technologies for energy production from artificial photosynthesis. ”

Next up in Fischer’s lab, Johnson plans to work with others to try and mutate a cyanobacteria to “go backwards” and perform manganese-oxidizing photosynthesis. The team also plans to investigate a set of rocks from western Australia that are similar in age to the samples used in the current study and may also contain beds of manganese. If their current study results are truly an indication of manganese-oxidizing photosynthesis, they say, there should be evidence of the same processes in other parts of the world.

“Oxygen is the backdrop on which this story is playing out on, but really, this is a tale of the evolution of this very intense metabolism that happened once-an evolutionary singularity that transformed the planet,” Fischer says. “We’ve provided insight into how the evolution of one of these remarkable molecular machines led up to the oxidation of our planet’s atmosphere, and now we’re going to follow up on all angles of our findings.”

Location of upwelling in Earth’s mantle discovered to be stable

This is a diagram showing a slice through the Earth's mantle, cutting across major mantle upwelling locations beneath Africa and the Pacific. -  C. Conrad (UH SOEST)
This is a diagram showing a slice through the Earth’s mantle, cutting across major mantle upwelling locations beneath Africa and the Pacific. – C. Conrad (UH SOEST)

A study published in Nature today shares the discovery that large-scale upwelling within Earth’s mantle mostly occurs in only two places: beneath Africa and the Central Pacific. More importantly, Clinton Conrad, Associate Professor of Geology at the University of Hawaii – Manoa’s School of Ocean and Earth Science and Technology (SOEST) and colleagues revealed that these upwelling locations have remained remarkably stable over geologic time, despite dramatic reconfigurations of tectonic plate motions and continental locations on the Earth’s surface. “For example,” said Conrad, “the Pangaea supercontinent formed and broke apart at the surface, but we think that the upwelling locations in the mantle have remained relatively constant despite this activity.”

Conrad has studied patterns of tectonic plates throughout his career, and has long noticed that the plates were, on average, moving northward. “Knowing this,” explained Conrad, “I was curious if I could determine a single location in the Northern Hemisphere toward which all plates are converging, on average.” After locating this point in eastern Asia, Conrad then wondered if other special points on Earth could characterize plate tectonics. “With some mathematical work, I described the plate tectonic ‘quadrupole’, which defines two points of ‘net convergence’ and two points of ‘net divergence’ of tectonic plate motions.”

When the researchers computed the plate tectonic quadruople locations for present-day plate motions, they found that the net divergence locations were consistent with the African and central Pacific locations where scientists think that mantle upwellings are occurring today. “This observation was interesting and important, and it made sense,” said Conrad. “Next, we applied this formula to the time history of plate motions and plotted the points – I was astonished to see that the points have not moved over geologic time!” Because plate motions are merely the surface expression of the underlying dynamics of the Earth’s mantle, Conrad and his colleagues were able to infer that upwelling flow in the mantle must also remain stable over geologic time. “It was as if I was seeing the ‘ghosts’ of ancient mantle flow patterns, recorded in the geologic record of plate motions!”

Earth’s mantle dynamics govern many aspects of geologic change on the Earth’s surface. This recent discovery that mantle upwelling has remained stable and centered on two locations (beneath Africa and the Central Pacific) provides a framework for understanding how mantle dynamics can be linked to surface geology over geologic time. For example, the researchers can now estimate how individual continents have moved relative to these two upwelling locations. This allows them to tie specific events that are observed in the geologic record to the mantle forces that ultimately caused these events.

More broadly, this research opens up a big question for solid earth scientists: What processes cause these two mantle upwelling locations to remain stable within a complex and dynamically evolving system such as the mantle? One notable observation is that the lowermost mantle beneath Africa and the Central Pacific seems to be composed of rock assemblages that are different than the rest of the mantle. Is it possible that these two anomalous regions at the bottom of the mantle are somehow organizing flow patterns for the rest of the mantle? How?

“Answering such questions is important because geologic features such as ocean basins, mountains belts, earthquakes and volcanoes ultimately result from Earth’s interior dynamics,” Conrad described. “Thus, it is important to understand the time-dependent nature of our planet’s interior dynamics in order to better understand the geological forces that affect the planetary surface that is our home.”

The mantle flow framework that can be defined as a result of this study allows geophysicists to predict surface uplift and subsidence patterns as a function of time. These vertical motions of continents and seafloor cause both local and global changes in sea level. In the future, Conrad wants to use this new understanding of mantle flow patterns to predict changes in sea level over geologic time. By comparing these predictions to observations of sea level change, he hopes to develop new constraints on the influence of mantle dynamics on sea level.

Stray gases found in water wells near shale gas sites

Homeowners living within one kilometer of shale gas wells appear to be at higher risk of having their drinking water contaminated by stray gases, according to a new Duke University-led study.

Duke scientists analyzed 141 drinking water samples from private water wells across northeastern Pennsylvania’s gas-rich Marcellus shale basin. Their study documented not only higher methane concentrations in drinking water within a kilometer of shale gas drilling — which past studies have shown — but higher ethane and propane concentrations as well.

Methane concentrations were six times higher and ethane concentrations were 23 times higher at homes within a kilometer of a shale gas well. Propane was detected in 10 samples, all of them from homes within a kilometer of drilling.

“The methane, ethane and propane data, and new evidence from hydrocarbon and helium isotopes, all suggest that drilling has affected some homeowners’ water,” said Robert B. Jackson, a professor of environmental sciences at Duke’s Nicholas School of the Environment. “In a minority of cases, the gas even looks Marcellus-like, probably caused by faulty well construction.”

The ethane and propane contamination data are “new and hard to refute,” Jackson stressed. “There is no biological source of ethane and propane in the region and Marcellus gas is high in both, and higher in concentration than the Upper Devonian gas found in-between.”

The team examined which factors might explain their results, including topography, distance to gas wells and distance to geologic features. “Distance to gas wells was, by far, the most significant factor influencing gases in the drinking water we sampled,” said Jackson.

The peer-reviewed findings will appear this week in the online Early Edition of the Proceedings of the National Academy of Sciences.

Hydraulic fracturing, also called hydrofracking or fracking, involves pumping water, sand and chemicals deep underground into horizontal gas wells at high pressure to crack open hydrocarbon-rich shale and extract natural gas. Accelerated shale gas drilling and hydrofracking in recent years has fueled concerns about contamination in nearby drinking water supplies.

Two previous peer-reviewed studies by Duke scientists found direct evidence of methane contamination in water wells near shale-gas drilling sites in northeastern Pennsylvania, as well as possible connectivity between deep brines and shallow aquifers. A third study conducted with U.S. Geological Survey scientists found no evidence of drinking water contamination from shale gas production in Arkansas. None of the studies have found evidence of contamination by fracking fluids.

“Our studies demonstrate that distances from drilling sites, as well as variations in local and regional geology, play major roles in determining the possible risk of groundwater impacts from shale gas development,” said Avner Vengosh, professor of geochemistry and water quality at Duke’s Nicholas School. “As such, they must be taken into consideration before drilling begins.”

“The helium data in this study are the first from a new tool kit we’ve devised for identifying contamination using noble gas isotopes,” said Duke research scientist Thomas H. Darrah. “These tools allow us to identify and trace contaminants with a high degree of certainty.”

Seismic gap outside of Istanbul

Earthquake researchers have now identified a 30 kilometers long and ten kilometers deep area along the North Anatolian fault zone just south of Istanbul that could be the starting point for a strong earthquake. The group of seismologists including Professor Marco Bohnhoff of the GFZ German Research Centre for Geosciences reported in the current online issue of the scientific journal Nature (Nature Communications, DOI: 10.1038/ncomms2999) that this potential earthquake source is only 15 to 20 kilometers from the historic city center of Istanbul.

The Istanbul-Marmara region of northwestern Turkey with a population of more than 15 million faces a high probability of being exposed to an earthquake of magnitude 7 or more. To better understand the processes taking place before a strong earthquake at a critically pressurized fault zone, a seismic monitoring network was built on the Princes Islands in the Sea of Marmara off Istanbul under the auspices of the Potsdam Helmholtz Centre GFZ together with the Kandilli Earthquake Observatory in Istanbul. The Princes Islands offer the only opportunity to monitor the seismic zone running below the seafloor from a distance of few kilometers.

The now available data allow the scientists around GFZ researcher Marco Bohnhoff to come to the conclusion that the area is locked in depth in front of the historic city of Istanbul: “The block we identified reaches ten kilometers deep along the fault zone and has displayed no seismic activity since measurements began over four years ago. This could be an indication that the expected Marmara earthquake could originate there”, says Bohnhoff.

This is also supported by the fact that the fracture zone of the last strong earthquake in the region, in 1999, ended precisely in this area – probably at the same structure, which has been impeding the progressive shift of the Anatolian plate in the south against the Eurasian plate in the north since 1766 and building up pressure. The results are also being compared with findings from other fault zones, such as the San Andreas Fault in California, to better understand the physical processes before an earthquake.

Currently, the GFZ is intensifying its activity to monitor the earthquake zone in front of Istanbul. Together with the Disaster and Emergency Management Presidency of Turkey AFAD, several 300 meter deep holes are currently being drilled around the eastern Marmara Sea, into which highly sensitive borehole seismometers will be placed. With this Geophysical borehole Observatory at the North Anatolian Fault GONAF, measurement accuracy and detection threshold for microearthquakes are improved many times over. In addition, the new data also provide insights on the expected ground motion in the event of an earthquake in the region. Bohnhoff: “Earthquake prediction is scientifically impossible. But studies such as this provide a way to better characterize earthquakes in advance in terms of location, magnitude and rupture progression, and therefore allow a better assessment of damage risk.”

New ‘embryonic’ subduction zone found

A new subduction zone forming off the coast of Portugal heralds the beginning of a cycle that will see the Atlantic Ocean close as continental Europe moves closer to America.

Published in Geology, new research led by Monash University geologists has detected the first evidence that a passive margin in the Atlantic ocean is becoming active. Subduction zones, such as the one beginning near Iberia, are areas where one of the tectonic plates that cover the Earth’s surface dives beneath another plate into the mantle – the layer just below the crust.

Lead author Dr João Duarte, from the School of Geosciences said the team mapped the ocean floor and found it was beginning to fracture, indicating tectonic activity around the apparently passive South West Iberia plate margin.

“What we have detected is the very beginnings of an active margin – it’s like an embryonic subduction zone,” Dr Duarte said.

“Significant earthquake activity, including the 1755 quake which devastated Lisbon, indicated that there might be convergent tectonic movement in the area. For the first time, we have been able to provide not only evidences that this is indeed the case, but also a consistent driving mechanism.”

The incipient subduction in the Iberian zone could signal the start of a new phase of the Wilson Cycle – where plate movements break up supercontinents, like Pangaea, and open oceans, stabilise and then form new subduction zones which close the oceans and bring the scattered continents back together.

This break-up and reformation of supercontinents has happened at least three times, over more than four billion years, on Earth. The Iberian subduction will gradually pull Iberia towards the United States over approximately 220 million years.

The findings provide a unique opportunity to observe a passive margin becoming active – a process that will take around 20 million years. Even at this early phase the site will yield data that is crucial to refining the geodynamic models.

“Understanding these processes will certainly provide new insights on how subduction zones may have initiated in the past and how oceans start to close,” Dr Duarte said.

First risk assessment of shale gas fracking to biodiversity

Fracking, the controversial method of mining shale gas, is widespread across Pennsylvania, covering up to 280,000 km² of the Appalachian Basin. New research in the Annals of the New York Academy of Sciences explores the threat posed to biodiversity including pollution from toxic chemicals, the building of well pads and pipelines, and changes to wetlands.

“Shale gas has engendered a great deal of controversy, largely because of its impact on human health, but effects on biological diversity and resources have scarcely been addressed in the public debate,” said study author Erik Kiviat.

“This study indicated a wide range of potential impacts, some of which could be severe, including salinization of soils and surface waters and fragmentation of forests. The degree of industrialization of shale gas landscapes, and the 285,000 km² extent of the Marcellus and Utica shale gas region alone, should require great caution regarding impacts on biodiversity.”

Water is no lubricant

Water in the Earth’s crust and upper mantle may not play such an important role as a lubricant of plate tectonics as previously assumed. This is a result geoscientists present in the current issue of the scientific journal Nature (13/06/2013) after the examination of water in the mineral olivine.

Laboratory experiments over the past three decades have suggested the presence of water greatly weakens the mechanical strength of the mineral olivine, a key component of the Earth’s upper mantle. In a recent study led by the Bayerisches Geoinstitut in Bayreuth, the Secondary Ion Mass Spectrometer (SIMS) facility at the Potsdam based GFZ German Research Centre for Geosciences was used to reassess the importance of water in defining the rigidity of olivine.

While earlier studies were based on mineral aggregates, the SIMS method enabled a look at the role of water in single olivine crystals at the near-atomic scale.

Michael Wiedenbeck, who conducted the SIMS experiment at the GFZ: “We discovered that water has a much, much lower effect in terms of the mechanical weakening of olivine as previously believed. The new observations call for a reassessment of the role of water within the Earth’s interior.” One important consequence is that the earlier concept, indicating that water provides lubrication for continental drift, needs to be carefully reconsidered

Preparing for the next megathrust

Understanding the size and frequency of large earthquakes along the Pacific coast of North America is of great importance, not just to scientists, but also to government planners and the general public. The only way to predict the frequency and intensity of the ground motion expected from large and giant “megathrust ” earthquakes along Canada’s west coast is to analyze the geologic record. A new study published today in the Canadian Journal of Earth Sciences presents an exceptionally well-dated first record of earthquake history along the south coast of BC. Using a new high-resolution age model, a team of scientists meticulously identified and dated the disturbed sedimentary layers in a 40-metre marine sediment core raised from Effingham Inlet. The disturbances appear to have been caused by large and megathrust earthquakes that have occurred over the past 11,000 years.

One of the co-authors of the study, Dr. Audrey Dallimore, Associate Professor at Royal Roads University explains: “Some BC coastal fjords preserve annually layered organic sediments going back all the way to deglacial times. In Effingham Inlet, on the west coast of Vancouver Island, these sediments reveal disturbances we interpret were caused by earthquakes. With our very detailed age model that includes 68 radiocarbon dates and the Mazama Ash deposit (a volcanic eruption that took place 6800 yrs ago); we have identified 22 earthquake shaking events over the last 11,000 years, giving an estimate of a recurrence interval for large and megathrust earthquakes of about 500 years. However, it appears that the time between major shaking events can stretch up to about a 1,000 years.

“The last megathrust earthquake originating from the Cascadia subduction zone occurred in 1700 AD. Therefore, we are now in the risk zone of another earthquake. Even though it could be tomorrow or perhaps even centuries before it occurs, paleoseismic studies such as this one can help us understand the nature and frequency of rupture along the Cascadia Subduction Zone, and help Canadian coastal communities to improve their hazard assessments and emergency preparedness plans.”

“This exceptionally well-dated paleoseismic study by Enkin et al., involved a multi-disciplinary team of Canadian university and federal government scientists, and a core from the 2002 international drill program Marges Ouest Nord Américaines (MONA) campaign,” says Dr. Olav Lian, an associate editor of the Canadian Journal of Earth Sciences, professor at the University of the Fraser Valley and Director of the university’s Luminescence Dating Laboratory. “It gives us our first glimpse back in geologic time, of the recurrence interval of large and megathrust earthquakes impacting the vulnerable BC outer coastline. It also supports paleoseismic data found in offshore marine sediment cores along the US portion of the Cascadia Subduction Zone, recently released in an important United States Geological Survey (USGS) paleoseismic study by a team of researchers led by Dr. Chris Goldfinger of Oregon State University. In addition to analyzing the Effingham Inlet record for earthquake events, this study site has also revealed much information about climate and ocean changes throughout the Holocene to the present. These findings also clearly illustrate the importance of analyzing the geologic record to help today’s planners and policy makers, and ultimately to increase the resiliency of Canadian communities. “

New study proposes solution to long-running debate as to how stable the Earth system is

Researchers at the University of Southampton have proposed an answer to the long-running debate as to how stable the Earth system is.

The Earth, with its core-driven magnetic field, oceans of liquid water, dynamic climate and abundant life is arguably the most complex system in the known Universe. Life arose on Earth over three and a half billion years ago and it would appear that despite planetary scale calamities such as the impacts of massive meteorites, runaway climate change and increases in brightness of the Sun, it has continued to grow, reproduce and evolve ever since.

Has life on Earth simply been lucky in withstanding these events or are there any self-stabilising processes operating in the Earth system that would reduce the severity of such perturbations? If such planetary processes exist, to what extent are they the result of the actions of life?

Forty years ago, James Lovelock formulated his Gaia Hypothesis in which life controls aspects of the planet and in doing so maintains conditions that are suitable for widespread life despite shocks and perturbations. This hypothesis was and remains controversial in part because there is no understood mechanism by which such a planetary self-stabilizing system could emerge.

In research published in PLOS Computational Biology, University of Southampton lecturer Dr James Dyke and PhD student Iain Weaver detail a mechanism that shows how when life is both affected by and alters environmental conditions, then what emerges is a control system that stabilises environmental conditions. This control system was first described around the middle of the 20th Century during the development of the cybernetics movement and has until now been largely neglected. Their findings are in principle applicable to a wide range of real world systems – from microbial mats to aquatic ecosystems up to and including the entire biosphere.

Dr Dyke says: “As well as being a fascinating issue in its own right, we quite desperately need to understand what is currently happening to the Earth and in particular the impacts of our own behaviour.

“Pretty much whatever we do, life on Earth will carry on, just as it did for the previous 3.5 billion years or so. It is only by discovering the mechanisms by which our living planet has evolved in the past can we hope to continue to be part of its future.”