Fracking’s environmental impacts scrutinized

Greenhouse gas emissions from the production and use of shale gas would be comparable to conventional natural gas, but the controversial energy source actually faired better than renewables on some environmental impacts, according to new research.

The UK holds enough shale gas to supply its entire gas demand for 470 years, promising to solve the country’s energy crisis and end its reliance on fossil-fuel imports from unstable markets. But for many, including climate scientists and environmental groups, shale gas exploitation is viewed as environmentally dangerous and would result in the UK reneging on its greenhouse gas reduction obligations under the Climate Change Act.

University of Manchester scientists have now conducted one of the most thorough examinations of the likely environmental impacts of shale gas exploitation in the UK in a bid to inform the debate. Their research has just been published in the leading academic journal Applied Energy and study lead author, Professor Adisa Azapagic, will outline the findings at the Labour Party Conference in Manchester, England, today (Monday, 22 September).

“While exploration is currently ongoing in the UK, commercial extraction of shale gas has not yet begun, yet its potential has stirred controversy over its environmental impacts, its safety and the difficulty of justifying its use to a nation conscious of climate change,” said Professor Azapagic.

“There are many unknowns in the debate surrounding shale gas, so we have attempted to address some of these unknowns by estimating its life cycle environmental impacts from ‘cradle to grave’. We looked at 11 different impacts from the extraction of shale gas using hydraulic fracturing – known as ‘fracking’- as well as from its processing and use to generate electricity.”

The researchers compared shale gas to other fossil-fuel alternatives, such as conventional natural gas and coal, as well as low-carbon options, including nuclear, offshore wind and solar power (solar photovoltaics).

The results of the research suggest that the average emissions of greenhouse gases from shale gas over its entire life cycle are about 460 grams of carbon dioxide-equivalent per kilowatt-hour of electricity generated. This, the authors say, is comparable to the emissions from conventional natural gas. For most of the other life-cycle environmental impacts considered by the team, shale gas was also comparable to conventional natural gas.

But the study also found that shale gas was better than offshore wind and solar for four out of 11 impacts: depletion of natural resources, toxicity to humans, as well as the impact on freshwater and marine organisms. Additionally, shale gas was better than solar (but not wind) for ozone layer depletion and eutrophication (the effect of nutrients such as phosphates, on natural ecosystems).

On the other hand, shale gas was worse than coal for three impacts: ozone layer depletion, summer smog and terrestrial eco-toxicity.

Professor Azapagic said: “Some of the impacts of solar power are actually relatively high, so it is not a complete surprise that shale gas is better in a few cases. This is mainly because manufacturing solar panels is very energy and resource-intensive, while their electrical output is quite low in a country like the UK, as we don’t have as much sunshine. However, our research shows that the environmental impacts of shale gas can vary widely, depending on the assumptions for various parameters, including the composition and volume of the fracking fluid used, disposal routes for the drilling waste and the amount of shale gas that can be recovered from a well.

“Assuming the worst case conditions, several of the environmental impacts from shale gas could be worse than from any other options considered in the research, including coal. But, under the best-case conditions, shale gas may be preferable to imported liquefied natural gas.”

The authors say their results highlight the need for tight regulation of shale gas exploration – weak regulation, they claim, may result in shale gas having higher impacts than coal power, resulting in a failure to meet climate change and sustainability imperatives and undermining the deployment of low-carbon technologies.

Professor Azapagic added: “Whether shale gas is an environmentally sound option depends on the perceived importance of different environmental impacts and the regulatory structure under which shale gas operates.

“From the government policy perspective – focusing mainly on economic growth and energy security – it appears likely that shale gas represents a good option for the UK energy sector, assuming that it can be extracted at reasonable cost.

“However, a wider view must also consider other aspects of widespread use of shale gas, including the impact on climate change, as well as many other environmental considerations addressed in our study. Ultimately, the environmental impacts from shale gas will depend on which options it is displacing and how tight the regulation is.”

Study co-author Dr Laurence Stamford, from Manchester’s School of Chemical Engineering and Analytical Science, said: “Appropriate regulation should introduce stringent controls on the emissions from shale gas extraction and disposal of drilling waste. It should also discourage extraction from sites where there is little shale gas in order to avoid the high emissions associated with a low-output well.

He continued: “If shale gas is extracted under tight regulations and is reasonably cheap, there is no obvious reason, as yet, why it should not make some contribution to our energy mix. However, regulation should also ensure that investment in sustainable technologies is not reduced at the expense of shale gas.”

Fracking’s environmental impacts scrutinized

Greenhouse gas emissions from the production and use of shale gas would be comparable to conventional natural gas, but the controversial energy source actually faired better than renewables on some environmental impacts, according to new research.

The UK holds enough shale gas to supply its entire gas demand for 470 years, promising to solve the country’s energy crisis and end its reliance on fossil-fuel imports from unstable markets. But for many, including climate scientists and environmental groups, shale gas exploitation is viewed as environmentally dangerous and would result in the UK reneging on its greenhouse gas reduction obligations under the Climate Change Act.

University of Manchester scientists have now conducted one of the most thorough examinations of the likely environmental impacts of shale gas exploitation in the UK in a bid to inform the debate. Their research has just been published in the leading academic journal Applied Energy and study lead author, Professor Adisa Azapagic, will outline the findings at the Labour Party Conference in Manchester, England, today (Monday, 22 September).

“While exploration is currently ongoing in the UK, commercial extraction of shale gas has not yet begun, yet its potential has stirred controversy over its environmental impacts, its safety and the difficulty of justifying its use to a nation conscious of climate change,” said Professor Azapagic.

“There are many unknowns in the debate surrounding shale gas, so we have attempted to address some of these unknowns by estimating its life cycle environmental impacts from ‘cradle to grave’. We looked at 11 different impacts from the extraction of shale gas using hydraulic fracturing – known as ‘fracking’- as well as from its processing and use to generate electricity.”

The researchers compared shale gas to other fossil-fuel alternatives, such as conventional natural gas and coal, as well as low-carbon options, including nuclear, offshore wind and solar power (solar photovoltaics).

The results of the research suggest that the average emissions of greenhouse gases from shale gas over its entire life cycle are about 460 grams of carbon dioxide-equivalent per kilowatt-hour of electricity generated. This, the authors say, is comparable to the emissions from conventional natural gas. For most of the other life-cycle environmental impacts considered by the team, shale gas was also comparable to conventional natural gas.

But the study also found that shale gas was better than offshore wind and solar for four out of 11 impacts: depletion of natural resources, toxicity to humans, as well as the impact on freshwater and marine organisms. Additionally, shale gas was better than solar (but not wind) for ozone layer depletion and eutrophication (the effect of nutrients such as phosphates, on natural ecosystems).

On the other hand, shale gas was worse than coal for three impacts: ozone layer depletion, summer smog and terrestrial eco-toxicity.

Professor Azapagic said: “Some of the impacts of solar power are actually relatively high, so it is not a complete surprise that shale gas is better in a few cases. This is mainly because manufacturing solar panels is very energy and resource-intensive, while their electrical output is quite low in a country like the UK, as we don’t have as much sunshine. However, our research shows that the environmental impacts of shale gas can vary widely, depending on the assumptions for various parameters, including the composition and volume of the fracking fluid used, disposal routes for the drilling waste and the amount of shale gas that can be recovered from a well.

“Assuming the worst case conditions, several of the environmental impacts from shale gas could be worse than from any other options considered in the research, including coal. But, under the best-case conditions, shale gas may be preferable to imported liquefied natural gas.”

The authors say their results highlight the need for tight regulation of shale gas exploration – weak regulation, they claim, may result in shale gas having higher impacts than coal power, resulting in a failure to meet climate change and sustainability imperatives and undermining the deployment of low-carbon technologies.

Professor Azapagic added: “Whether shale gas is an environmentally sound option depends on the perceived importance of different environmental impacts and the regulatory structure under which shale gas operates.

“From the government policy perspective – focusing mainly on economic growth and energy security – it appears likely that shale gas represents a good option for the UK energy sector, assuming that it can be extracted at reasonable cost.

“However, a wider view must also consider other aspects of widespread use of shale gas, including the impact on climate change, as well as many other environmental considerations addressed in our study. Ultimately, the environmental impacts from shale gas will depend on which options it is displacing and how tight the regulation is.”

Study co-author Dr Laurence Stamford, from Manchester’s School of Chemical Engineering and Analytical Science, said: “Appropriate regulation should introduce stringent controls on the emissions from shale gas extraction and disposal of drilling waste. It should also discourage extraction from sites where there is little shale gas in order to avoid the high emissions associated with a low-output well.

He continued: “If shale gas is extracted under tight regulations and is reasonably cheap, there is no obvious reason, as yet, why it should not make some contribution to our energy mix. However, regulation should also ensure that investment in sustainable technologies is not reduced at the expense of shale gas.”

First eyewitness accounts of mystery volcanic eruption

This eruption occurred just before the 1815 Tambora volcanic eruption which is famous for its impact on climate worldwide, with 1816 given memorable names such as ‘Eighteen-Hundred-and-Froze-to-Death’, the ‘Year of the Beggar’ and the ‘Year Without a Summer’ because of unseasonal frosts, crop failure and famine across Europe and North America. The extraordinary conditions are considered to have inspired literary works such as Byron’s ‘Darkness’ and Mary Shelley’s Frankenstein.

However, the global deterioration of the 1810s into the coldest decade in the last 500 years started six years earlier, with another large eruption. In contrast to Tambora, this so-called ‘Unknown’ eruption seemingly occurred unnoticed, with both its location and date a mystery. In fact the ‘Unknown’ eruption was only recognised in the 1990s, from tell-tale markers in Greenland and Antarctic ice that record the rare events when volcanic aerosols are so violently erupted that they reach the Earth’s stratosphere.

Working in collaboration with colleagues from the School of Earth Sciences and PhD student Alvaro Guevara-Murua, Dr Caroline Williams, from the Department of Hispanic, Portuguese and Latin American Studies, began searching historical archives for references to the event.

Dr Williams said: “I spent months combing through the vast Spanish colonial archive, but it was a fruitless search – clearly the volcano wasn’t in Latin America. I then turned to the writings of Colombian scientist Francisco José de Caldas, who served as Director of the Astronomical Observatory of Bogotá between 1805 and 1810. Finding his precise description of the effects of an eruption was a ‘Eureka’ moment.”

In February 1809 Caldas wrote about a “mystery” that included a constant, stratospheric “transparent cloud that obstructs the sun’s brilliance” over Bogotá, starting on the 11 December 1808 and seen across Colombia. He gave detailed observations, for example that the “natural fiery colour [of the sun] has changed to that of silver, so much so that many have mistaken it for the moon”; and that the weather was unusually cold, the fields covered with ice and the crops damaged by frost.

Unearthing a short account written by physician José Hipólito Unanue in Lima, Peru, describing sunset after-glows (a common atmospheric effect caused by volcanic aerosols in the stratosphere) at the same time as Caldas’ “vapours above the horizon”, enabled the researchers to verify that the atmospheric effects of the eruption were seen at the same time on both sides of the equator.

These two 19th century Latin American scientists provide the first direct observations that can be linked to the ‘Unknown’ eruption. More importantly, the accounts date the eruption to within a fortnight of 4 December 1808.

Dr Erica Hendy said: “There have to be more observations hidden away, for example in ship logs. Having a date for the eruption will now make it much easier to track these down, and maybe even pinpoint the volcano. Climate modelling of this fascinating decade will also now be more accurate because the season of the eruption determines how the aerosols disperse around the globe and where climatic effects are felt.”

Alvaro Guevara-Murua added: “This study has meant delving into many fields of research – obviously paleoclimatology and volcanology, but also 19th century meteorology and Spanish colonial history – and has also needed rigorous precision to correctly translate the words of two scientists writing 200 years ago. Giving them a voice in modern science has been a big responsibility.”

One further question remains: why are there so few historical accounts of what was clearly a significant event with wide-reaching consequences? Perhaps, Dr Williams suggests, the political environment on both sides of the Atlantic at the beginning of the nineteenth century played a part.

“The eruption coincided with the Napoleonic Wars in Europe, the Peninsular War in Spain, and with political developments in Latin America that would soon lead to the independence of almost all of Spain’s American colonies. It’s possible that, in Europe and Latin America at least, the attention of individuals who might otherwise have provided us with a record of unusual meteorological or atmospheric effects simply turned to military and political matters instead,” she said.

First eyewitness accounts of mystery volcanic eruption

This eruption occurred just before the 1815 Tambora volcanic eruption which is famous for its impact on climate worldwide, with 1816 given memorable names such as ‘Eighteen-Hundred-and-Froze-to-Death’, the ‘Year of the Beggar’ and the ‘Year Without a Summer’ because of unseasonal frosts, crop failure and famine across Europe and North America. The extraordinary conditions are considered to have inspired literary works such as Byron’s ‘Darkness’ and Mary Shelley’s Frankenstein.

However, the global deterioration of the 1810s into the coldest decade in the last 500 years started six years earlier, with another large eruption. In contrast to Tambora, this so-called ‘Unknown’ eruption seemingly occurred unnoticed, with both its location and date a mystery. In fact the ‘Unknown’ eruption was only recognised in the 1990s, from tell-tale markers in Greenland and Antarctic ice that record the rare events when volcanic aerosols are so violently erupted that they reach the Earth’s stratosphere.

Working in collaboration with colleagues from the School of Earth Sciences and PhD student Alvaro Guevara-Murua, Dr Caroline Williams, from the Department of Hispanic, Portuguese and Latin American Studies, began searching historical archives for references to the event.

Dr Williams said: “I spent months combing through the vast Spanish colonial archive, but it was a fruitless search – clearly the volcano wasn’t in Latin America. I then turned to the writings of Colombian scientist Francisco José de Caldas, who served as Director of the Astronomical Observatory of Bogotá between 1805 and 1810. Finding his precise description of the effects of an eruption was a ‘Eureka’ moment.”

In February 1809 Caldas wrote about a “mystery” that included a constant, stratospheric “transparent cloud that obstructs the sun’s brilliance” over Bogotá, starting on the 11 December 1808 and seen across Colombia. He gave detailed observations, for example that the “natural fiery colour [of the sun] has changed to that of silver, so much so that many have mistaken it for the moon”; and that the weather was unusually cold, the fields covered with ice and the crops damaged by frost.

Unearthing a short account written by physician José Hipólito Unanue in Lima, Peru, describing sunset after-glows (a common atmospheric effect caused by volcanic aerosols in the stratosphere) at the same time as Caldas’ “vapours above the horizon”, enabled the researchers to verify that the atmospheric effects of the eruption were seen at the same time on both sides of the equator.

These two 19th century Latin American scientists provide the first direct observations that can be linked to the ‘Unknown’ eruption. More importantly, the accounts date the eruption to within a fortnight of 4 December 1808.

Dr Erica Hendy said: “There have to be more observations hidden away, for example in ship logs. Having a date for the eruption will now make it much easier to track these down, and maybe even pinpoint the volcano. Climate modelling of this fascinating decade will also now be more accurate because the season of the eruption determines how the aerosols disperse around the globe and where climatic effects are felt.”

Alvaro Guevara-Murua added: “This study has meant delving into many fields of research – obviously paleoclimatology and volcanology, but also 19th century meteorology and Spanish colonial history – and has also needed rigorous precision to correctly translate the words of two scientists writing 200 years ago. Giving them a voice in modern science has been a big responsibility.”

One further question remains: why are there so few historical accounts of what was clearly a significant event with wide-reaching consequences? Perhaps, Dr Williams suggests, the political environment on both sides of the Atlantic at the beginning of the nineteenth century played a part.

“The eruption coincided with the Napoleonic Wars in Europe, the Peninsular War in Spain, and with political developments in Latin America that would soon lead to the independence of almost all of Spain’s American colonies. It’s possible that, in Europe and Latin America at least, the attention of individuals who might otherwise have provided us with a record of unusual meteorological or atmospheric effects simply turned to military and political matters instead,” she said.

What set the Earth’s plates in motion?

The image shows a snapshot from the film after 45 million years of spreading. The pink is the region where the mantle underneath the early continent has melted, facilitating its spreading, and the initiation of the plate tectonic process. -  Patrice Rey, Nicolas Flament and Nicolas Coltice.
The image shows a snapshot from the film after 45 million years of spreading. The pink is the region where the mantle underneath the early continent has melted, facilitating its spreading, and the initiation of the plate tectonic process. – Patrice Rey, Nicolas Flament and Nicolas Coltice.

The mystery of what kick-started the motion of our earth’s massive tectonic plates across its surface has been explained by researchers at the University of Sydney.

“Earth is the only planet in our solar system where the process of plate tectonics occurs,” said Professor Patrice Rey, from the University of Sydney’s School of Geosciences.

“The geological record suggests that until three billion years ago the earth’s crust was immobile so what sparked this unique phenomenon has fascinated geoscientists for decades. We suggest it was triggered by the spreading of early continents then eventually became a self-sustaining process.”

Professor Rey is lead author of an article on the findings published in Nature on Wednesday, 17 September.

The other authors on the paper are Nicolas Flament, also from the School of Geosciences and Nicolas Coltice, from the University of Lyon.

There are eight major tectonic plates that move above the earth’s mantle at rates up to 150 millimetres every year.

In simple terms the process involves plates being dragged into the mantle at certain points and moving away from each other at others, in what has been dubbed ‘the conveyor belt’.

Plate tectonics depends on the inverse relationship between density of rocks and temperature.

At mid-oceanic ridges, rocks are hot and their density is low, making them buoyant or more able to float. As they move away from those ridges they cool down and their density increases until, where they become denser than the underlying hot mantle, they sink and are ‘dragged’ under.

But three to four billion years ago, the earth’s interior was hotter, volcanic activity was more prominent and tectonic plates did not become cold and dense enough to spontaneously sank.

“So the driving engine for plate tectonics didn’t exist,” said Professor Rey said.

“Instead, thick and buoyant early continents erupted in the middle of immobile plates. Our modelling shows that these early continents could have placed major stress on the surrounding plates. Because they were buoyant they spread horizontally, forcing adjacent plates to be pushed under at their edges.”

“This spreading of the early continents could have produced intermittent episodes of plate tectonics until, as the earth’s interior cooled and its crust and plate mantle became heavier, plate tectonics became a self-sustaining process which has never ceased and has shaped the face of our modern planet.”

The new model also makes a number of predictions explaining features that have long puzzled the geoscience community.



Video
Click on this image to view the .mp4 video
The movie tells an 87-million-year-long story. It shows an early buoyant continent (made of a residual mantle in green and continental crust in red) slowly spreading toward the adjacent immobile plate (blue). After 45 million years, a short-lived subduction zone, where the plate goes under, develops. This allows the continent to surge toward the ocean, leading to the detachment of a continental block, the starting step in the movement of the continental plates or plate tectonics. – Patrice Rey, Nicolas Flament and Nicolas Coltice

What set the Earth’s plates in motion?

The image shows a snapshot from the film after 45 million years of spreading. The pink is the region where the mantle underneath the early continent has melted, facilitating its spreading, and the initiation of the plate tectonic process. -  Patrice Rey, Nicolas Flament and Nicolas Coltice.
The image shows a snapshot from the film after 45 million years of spreading. The pink is the region where the mantle underneath the early continent has melted, facilitating its spreading, and the initiation of the plate tectonic process. – Patrice Rey, Nicolas Flament and Nicolas Coltice.

The mystery of what kick-started the motion of our earth’s massive tectonic plates across its surface has been explained by researchers at the University of Sydney.

“Earth is the only planet in our solar system where the process of plate tectonics occurs,” said Professor Patrice Rey, from the University of Sydney’s School of Geosciences.

“The geological record suggests that until three billion years ago the earth’s crust was immobile so what sparked this unique phenomenon has fascinated geoscientists for decades. We suggest it was triggered by the spreading of early continents then eventually became a self-sustaining process.”

Professor Rey is lead author of an article on the findings published in Nature on Wednesday, 17 September.

The other authors on the paper are Nicolas Flament, also from the School of Geosciences and Nicolas Coltice, from the University of Lyon.

There are eight major tectonic plates that move above the earth’s mantle at rates up to 150 millimetres every year.

In simple terms the process involves plates being dragged into the mantle at certain points and moving away from each other at others, in what has been dubbed ‘the conveyor belt’.

Plate tectonics depends on the inverse relationship between density of rocks and temperature.

At mid-oceanic ridges, rocks are hot and their density is low, making them buoyant or more able to float. As they move away from those ridges they cool down and their density increases until, where they become denser than the underlying hot mantle, they sink and are ‘dragged’ under.

But three to four billion years ago, the earth’s interior was hotter, volcanic activity was more prominent and tectonic plates did not become cold and dense enough to spontaneously sank.

“So the driving engine for plate tectonics didn’t exist,” said Professor Rey said.

“Instead, thick and buoyant early continents erupted in the middle of immobile plates. Our modelling shows that these early continents could have placed major stress on the surrounding plates. Because they were buoyant they spread horizontally, forcing adjacent plates to be pushed under at their edges.”

“This spreading of the early continents could have produced intermittent episodes of plate tectonics until, as the earth’s interior cooled and its crust and plate mantle became heavier, plate tectonics became a self-sustaining process which has never ceased and has shaped the face of our modern planet.”

The new model also makes a number of predictions explaining features that have long puzzled the geoscience community.



Video
Click on this image to view the .mp4 video
The movie tells an 87-million-year-long story. It shows an early buoyant continent (made of a residual mantle in green and continental crust in red) slowly spreading toward the adjacent immobile plate (blue). After 45 million years, a short-lived subduction zone, where the plate goes under, develops. This allows the continent to surge toward the ocean, leading to the detachment of a continental block, the starting step in the movement of the continental plates or plate tectonics. – Patrice Rey, Nicolas Flament and Nicolas Coltice

Meteorite that doomed the dinosaurs helped the forests bloom

<IMG SRC="/Images/537934362.jpg" WIDTH="350" HEIGHT="233" BORDER="0" ALT="Seen here is a Late Cretaceous specimen from the Hell Creek Formation, morphotype HC62, taxon
''Rhamnus” cleburni. Specimens are housed at the Denver Museum of Nature and Science in
Denver, Colorado. – Image credit: Benjamin Blonder.”>
Seen here is a Late Cretaceous specimen from the Hell Creek Formation, morphotype HC62, taxon
Rhamnus” cleburni. Specimens are housed at the Denver Museum of Nature and Science in
Denver, Colorado. – Image credit: Benjamin Blonder.

66 million years ago, a 10-km diameter chunk of rock hit the Yukatan peninsula near the site of the small town of Chicxulub with the force of 100 teratons of TNT. It left a crater more than 150 km across, and the resulting megatsunami, wildfires, global earthquakes and volcanism are widely accepted to have wiped out the dinosaurs and made way for the rise of the mammals. But what happened to the plants on which the dinosaurs fed?

A new study led by researchers from the University of Arizona reveals that the meteorite impact that spelled doom for the dinosaurs also decimated the evergreen flowering plants to a much greater extent than their deciduous peers. They hypothesize that the properties of deciduous plants made them better able to respond rapidly to chaotically varying post-apocalyptic climate conditions. The results are publishing on September 16 in the open access journal PLOS Biology.

Applying biomechanical formulae to a treasure trove of thousands of fossilized leaves of angiosperms – flowering plants excluding conifers – the team was able to reconstruct the ecology of a diverse plant community thriving during a 2.2 million-year period spanning the cataclysmic impact event, believed to have wiped out more than half of plant species living at the time. The fossilized leaf samples span the last 1,400,000 years of the Cretaceous and the first 800,000 of the Paleogene.

The researchers found evidence that after the impact, fast-growing, deciduous angiosperms had replaced their slow-growing, evergreen peers to a large extent. Living examples of evergreen angiosperms, such as holly and ivy, tend to prefer shade, don’t grow very fast and sport dark-colored leaves.

“When you look at forests around the world today, you don’t see many forests dominated by evergreen flowering plants,” said the study’s lead author, Benjamin Blonder. “Instead, they are dominated by deciduous species, plants that lose their leaves at some point during the year.”

Blonder and his colleagues studied a total of about 1,000 fossilized plant leaves collected from a location in southern North Dakota, embedded in rock layers known as the Hell Creek Formation, which at the end of the Cretaceous was a lowland floodplain crisscrossed by river channels. The collection consists of more than 10,000 identified plant fossils and is housed primarily at the Denver Museum of Nature and Science. “When you hold one of those leaves that is so exquisitely preserved in your hand knowing it’s 66 million years old, it’s a humbling feeling,” said Blonder.

“If you think about a mass extinction caused by catastrophic event such as a meteorite impacting Earth, you might imagine all species are equally likely to die,” Blonder said. “Survival of the fittest doesn’t apply – the impact is like a reset button. The alternative hypothesis, however, is that some species had properties that enabled them to survive.

“Our study provides evidence of a dramatic shift from slow-growing plants to fast-growing species,” he said. “This tells us that the extinction was not random, and the way in which a plant acquires resources predicts how it can respond to a major disturbance. And potentially this also tells us why we find that modern forests are generally deciduous and not evergreen.”

Previously, other scientists found evidence of a dramatic drop in temperature caused by dust from the impact. “The hypothesis is that the impact winter introduced a very variable climate,” Blonder said. “That would have favored plants that grew quickly and could take advantage of changing conditions, such as deciduous plants.”

“We measured the mass of a given leaf in relation to its area, which tells us whether the leaf was a chunky, expensive one to make for the plant, or whether it was a more flimsy, cheap one,” Blonder explained. “In other words, how much carbon the plant had invested in the leaf.” In addition the researchers measured the density of the leaves’ vein networks, a measure of the amount of water a plant can transpire and the rate at which it can acquire carbon.

“There is a spectrum between fast- and slow-growing species,” said Blonder. “There is the ‘live fast, die young’ strategy and there is the ‘slow but steady’ strategy. You could compare it to financial strategies investing in stocks versus bonds.” The analyses revealed that while slow-growing evergreens dominated the plant assemblages before the extinction event, fast-growing flowering species had taken their places afterward.

Meteorite that doomed the dinosaurs helped the forests bloom

<IMG SRC="/Images/537934362.jpg" WIDTH="350" HEIGHT="233" BORDER="0" ALT="Seen here is a Late Cretaceous specimen from the Hell Creek Formation, morphotype HC62, taxon
''Rhamnus” cleburni. Specimens are housed at the Denver Museum of Nature and Science in
Denver, Colorado. – Image credit: Benjamin Blonder.”>
Seen here is a Late Cretaceous specimen from the Hell Creek Formation, morphotype HC62, taxon
Rhamnus” cleburni. Specimens are housed at the Denver Museum of Nature and Science in
Denver, Colorado. – Image credit: Benjamin Blonder.

66 million years ago, a 10-km diameter chunk of rock hit the Yukatan peninsula near the site of the small town of Chicxulub with the force of 100 teratons of TNT. It left a crater more than 150 km across, and the resulting megatsunami, wildfires, global earthquakes and volcanism are widely accepted to have wiped out the dinosaurs and made way for the rise of the mammals. But what happened to the plants on which the dinosaurs fed?

A new study led by researchers from the University of Arizona reveals that the meteorite impact that spelled doom for the dinosaurs also decimated the evergreen flowering plants to a much greater extent than their deciduous peers. They hypothesize that the properties of deciduous plants made them better able to respond rapidly to chaotically varying post-apocalyptic climate conditions. The results are publishing on September 16 in the open access journal PLOS Biology.

Applying biomechanical formulae to a treasure trove of thousands of fossilized leaves of angiosperms – flowering plants excluding conifers – the team was able to reconstruct the ecology of a diverse plant community thriving during a 2.2 million-year period spanning the cataclysmic impact event, believed to have wiped out more than half of plant species living at the time. The fossilized leaf samples span the last 1,400,000 years of the Cretaceous and the first 800,000 of the Paleogene.

The researchers found evidence that after the impact, fast-growing, deciduous angiosperms had replaced their slow-growing, evergreen peers to a large extent. Living examples of evergreen angiosperms, such as holly and ivy, tend to prefer shade, don’t grow very fast and sport dark-colored leaves.

“When you look at forests around the world today, you don’t see many forests dominated by evergreen flowering plants,” said the study’s lead author, Benjamin Blonder. “Instead, they are dominated by deciduous species, plants that lose their leaves at some point during the year.”

Blonder and his colleagues studied a total of about 1,000 fossilized plant leaves collected from a location in southern North Dakota, embedded in rock layers known as the Hell Creek Formation, which at the end of the Cretaceous was a lowland floodplain crisscrossed by river channels. The collection consists of more than 10,000 identified plant fossils and is housed primarily at the Denver Museum of Nature and Science. “When you hold one of those leaves that is so exquisitely preserved in your hand knowing it’s 66 million years old, it’s a humbling feeling,” said Blonder.

“If you think about a mass extinction caused by catastrophic event such as a meteorite impacting Earth, you might imagine all species are equally likely to die,” Blonder said. “Survival of the fittest doesn’t apply – the impact is like a reset button. The alternative hypothesis, however, is that some species had properties that enabled them to survive.

“Our study provides evidence of a dramatic shift from slow-growing plants to fast-growing species,” he said. “This tells us that the extinction was not random, and the way in which a plant acquires resources predicts how it can respond to a major disturbance. And potentially this also tells us why we find that modern forests are generally deciduous and not evergreen.”

Previously, other scientists found evidence of a dramatic drop in temperature caused by dust from the impact. “The hypothesis is that the impact winter introduced a very variable climate,” Blonder said. “That would have favored plants that grew quickly and could take advantage of changing conditions, such as deciduous plants.”

“We measured the mass of a given leaf in relation to its area, which tells us whether the leaf was a chunky, expensive one to make for the plant, or whether it was a more flimsy, cheap one,” Blonder explained. “In other words, how much carbon the plant had invested in the leaf.” In addition the researchers measured the density of the leaves’ vein networks, a measure of the amount of water a plant can transpire and the rate at which it can acquire carbon.

“There is a spectrum between fast- and slow-growing species,” said Blonder. “There is the ‘live fast, die young’ strategy and there is the ‘slow but steady’ strategy. You could compare it to financial strategies investing in stocks versus bonds.” The analyses revealed that while slow-growing evergreens dominated the plant assemblages before the extinction event, fast-growing flowering species had taken their places afterward.

How a change in slope affects lava flows

When exposed to the elements, flowing lava will form a crust at its surface. -  Scott Rowland
When exposed to the elements, flowing lava will form a crust at its surface. – Scott Rowland

As soon as lava flows from a volcano, exposure to air and wind causes it to start to cool and harden. Rather than hardening evenly, the energy exchange tends to take place primarily at the surface. The cooling causes a crust to form on the outer edges of the lava flow, insulating the molten lava within. This hardened lava shell allows a lava flow to travel much further than it would otherwise, while cracks in the lava’s crust can cause it to draw up short.

When there is a break in the terrain-a sharp change in slope, a valley, or a rock wall, for example-the smooth lava flow is disrupted. Pulses in flow volume or the formation of turbulent eddies caused by these topographic features can make the hard lava shell crack. Using observations from historical eruptions and a simple mechanical model, Glaze et al. studied how changes in slope can affect lava flows. This was featured in a recent study in the Journal of Geophysical Research: Solid Earth.

The increase in flow velocity from a steepening slope is often quite minor, as most of the energy goes into vertical rotation of the lava, just as with a rock rolling down a hill. The authors’ model considers factors such as temperature, depth and flow velocity, along with the effect of lava viscosity, to calculate how a change in slope affects the formation of vertical eddies created by tumbling lava. The authors’ model allowed them to determine how far downstream the turbulence persists before the lava returns to a more streamlined flow.

How a change in slope affects lava flows

When exposed to the elements, flowing lava will form a crust at its surface. -  Scott Rowland
When exposed to the elements, flowing lava will form a crust at its surface. – Scott Rowland

As soon as lava flows from a volcano, exposure to air and wind causes it to start to cool and harden. Rather than hardening evenly, the energy exchange tends to take place primarily at the surface. The cooling causes a crust to form on the outer edges of the lava flow, insulating the molten lava within. This hardened lava shell allows a lava flow to travel much further than it would otherwise, while cracks in the lava’s crust can cause it to draw up short.

When there is a break in the terrain-a sharp change in slope, a valley, or a rock wall, for example-the smooth lava flow is disrupted. Pulses in flow volume or the formation of turbulent eddies caused by these topographic features can make the hard lava shell crack. Using observations from historical eruptions and a simple mechanical model, Glaze et al. studied how changes in slope can affect lava flows. This was featured in a recent study in the Journal of Geophysical Research: Solid Earth.

The increase in flow velocity from a steepening slope is often quite minor, as most of the energy goes into vertical rotation of the lava, just as with a rock rolling down a hill. The authors’ model considers factors such as temperature, depth and flow velocity, along with the effect of lava viscosity, to calculate how a change in slope affects the formation of vertical eddies created by tumbling lava. The authors’ model allowed them to determine how far downstream the turbulence persists before the lava returns to a more streamlined flow.