The secret behind Mona Lisa's enigmatic smile has been explained by scientists who believe it changes depending on which part of the eye sees it first.
One of the charms of the world's most famous painting is that she appears radiant one moment and then serious and sardonic the next.
Now scientists claim to have come up with an answer to her changing moods - our eyes are sending mixed signals to the brain. They believe Mona Lisa's smile depends on what cells in the retina pick up the image and what channel the image is transmitted through in the brain. Sometimes one channel wins over the other, and you see the smile, sometimes others take over and you do not see the smile.Different cells in the eye are designed to pick up different colours, contrasts, backgrounds and foregrounds. Some deal with central vision while others with peripheral.
Depending on what cells picks up the image first depends on what channel they are sent to the brian for interpreting.
These channels encode data about an object's size, clarity, brightness and location in the visual field."Sometimes one channel wins over the other, and you see the smile, sometimes others take over and you don't see the smile," said Dr Luis Martinez Otero, a neuroscientist at Institute of Neuroscience in Alicante, Spain, who conducted the study, told New Scientist.
To get a fuller picture of the reasons behind Mona Lisa's vanishing smile, Dr Martinez Otero varied different aspects of the Mona Lisa that are processed by different visual channels, and then asked volunteers whether they saw a smile or not.
To start with, the duo asked volunteers to look at the painting in varying sizes from varying distances. They found the closer you were the more likely you were to see the smile.
Next, Dr Martinez Otero's team compared how light affects our judgement of Mona Lisa's smile. Two kinds of cells determine the brightness of an object relative to its surroundings - "on-centre" cells, which are stimulated only when their centres are illuminated, and allow us to see a bright star in a dark night; and "off-centre" cells, which turn on only when their centres are dark, and allow us to pick out words on a printed page.
Dr Martinez Otero jammed these channels by showing another set of volunteers either a black or white screen for 30 seconds followed by a shot of the Mona Lisa. The black would mute off centre cells while the light on-centre. Volunteers were more likely to see Mona Lisa's smile after they had been shown the dark screen, leading Martinez Otero to conclude that it is these the on-centre cells that sense the Mona Lisa's smile.
Eye gaze also affects how volunteers see the smile, Martinez Otero says. His team used software to track where in the painting 20 volunteers gazed while they rated whether or not Mona Lisa's smile became more or less apparent.
With a minute to gaze at the painting, volunteers tended to focus on the left side of her mouth when judging her as smiling – further evidence that dead-centre vision picks out the smile.
When volunteers had only a fraction of a second to discern her smile, their eyes tended to focus on her left cheek, hinting that peripheral vision plays a role, too.
So did Leonardo intend to sow so much confusion in the brains of viewers, not to mention scientists? Absolutely, Martinez Otero contends. "He wrote in one of his notebooks that he was trying to paint dynamic expressions because that's what he saw in the street."
The research was originally presented at the Society for Neuroscience's annual meeting in Chicago.This isn't the first time scientists have deconstructed Leonardo da Vinci's masterpiece.
In 2000, Margaret Livingstone, a neuroscientist at Harvard Medical School with a side interest in art history, showed that Mona Lisa's smile is more apparent in peripheral visionMovie Camera than dead-centre vision.
This story can be read at the below link:
Thursday, November 5, 2009
Do "Skeleton" Filaments Give Structure to the Universe?
Are there "skeletons" out in the Universe –structures that form the framework of how galaxies are distributed? Astronomers have tracked down a gigantic, previously unknown assembly of galaxies located almost seven billion light-years away from us, which seems to point to a prominent galaxy structure in the distant Universe, providing further insight into the cosmic web and how it formed. “Matter is not distributed uniformly in the Universe,” says Masayuki Tanaka from ESO, who led the new study. “In our cosmic vicinity, stars form in galaxies and galaxies usually form groups and clusters of galaxies. The most widely accepted cosmological theories predict that matter also clumps on a larger scale in the so-called ‘cosmic web’, in which galaxies, embedded in filaments stretching between voids, create a gigantic wispy structure.”
More on this at:
Mild Exercise Boosts Lifespan Of Heart Patients
Mild exercise can significantly reduce the risk of early death from heart disease, according to a new study published in the American Journal of Medicine.
Just half an hour of jogging or riding a bike three times a week reduced the risk of early death by 60 percent, the research found.
Heart disease is the largest killer in the United States, and the number of people suffering from the condition is expected to rise as the population ages and obesity rates increase.
The study found that the most significant gains were realized in patients who were also stressed. Researchers believe this is due to the fact that stress can quadruple the risk of death in those with heart and circulation problems.
In these patients, exercise can offer the double benefit of reducing stress levels while also improving cardiovascular health.
“Exercise reduces mortality in patients with coronary artery disease…in part because of the effects on psycho social stress,” the researchers said.
Heart patients are typically put on drugs such as statins, which lower cholesterol levels, and blood pressure medication to reduce the risk of death from strokes, heart attacks and heart disease.
Previous studies have demonstrated a variety of life-extending benefits from exercise, including a reduced risk of cancer, heart disease and neurological disorders and slower rates of death and disability.
These benefits are due to the ability of exercise to improve the health of hearts and arteries, strengthen bones, lessen inflammation, boost the immune system and improve thinking, learning and memory.
The latest study, conducted by the Department of Cardiology in New Orleans, describes just how much these simple alterations can increase lifespan.
The researchers followed 522 cardiac patients, including 53 with high stress levels and 27 control patients who also had high stress levels but went without cardiac rehabilitation.
The patients were offered 12 weeks of exercise classes, which included a 10 minute warm-up, 30 to 40 minutes of aerobic exercise such as jogging, walking or rowing, and 10 minutes of stretching. The classes were conducted three times per week, with participants asked to do an additional one-to-three sessions each week on their own. The patients were also advised on lifestyle and diet improvements.
More on this at:
http://www.redorbit.com/news/health/1778952/mild_exercise_boosts_lifespan_of_heart_patients/index.html
Just half an hour of jogging or riding a bike three times a week reduced the risk of early death by 60 percent, the research found.
Heart disease is the largest killer in the United States, and the number of people suffering from the condition is expected to rise as the population ages and obesity rates increase.
The study found that the most significant gains were realized in patients who were also stressed. Researchers believe this is due to the fact that stress can quadruple the risk of death in those with heart and circulation problems.
In these patients, exercise can offer the double benefit of reducing stress levels while also improving cardiovascular health.
“Exercise reduces mortality in patients with coronary artery disease…in part because of the effects on psycho social stress,” the researchers said.
Heart patients are typically put on drugs such as statins, which lower cholesterol levels, and blood pressure medication to reduce the risk of death from strokes, heart attacks and heart disease.
Previous studies have demonstrated a variety of life-extending benefits from exercise, including a reduced risk of cancer, heart disease and neurological disorders and slower rates of death and disability.
These benefits are due to the ability of exercise to improve the health of hearts and arteries, strengthen bones, lessen inflammation, boost the immune system and improve thinking, learning and memory.
The latest study, conducted by the Department of Cardiology in New Orleans, describes just how much these simple alterations can increase lifespan.
The researchers followed 522 cardiac patients, including 53 with high stress levels and 27 control patients who also had high stress levels but went without cardiac rehabilitation.
The patients were offered 12 weeks of exercise classes, which included a 10 minute warm-up, 30 to 40 minutes of aerobic exercise such as jogging, walking or rowing, and 10 minutes of stretching. The classes were conducted three times per week, with participants asked to do an additional one-to-three sessions each week on their own. The patients were also advised on lifestyle and diet improvements.
http://www.redorbit.com/news/health/1778952/mild_exercise_boosts_lifespan_of_heart_patients/index.html
A New Wrinkle in Ancient Ocean Chemistry
Scientists widely accept that around 2.4 billion years ago, the Earth's atmosphere underwent a dramatic change when oxygen levels rose sharply. Called the "Great Oxidation Event" (GOE), the oxygen spike marks an important milestone in Earth's history, the transformation from an oxygen-poor atmosphere to an oxygen-rich one paving the way for complex life to develop on the planet.
Two questions that remain unresolved in studies of the early Earth are when oxygen production via photosynthesis got started and when it began to alter the chemistry of Earth's ocean and atmosphere.
Now a research team led by geoscientists at the University of California, Riverside corroborates recent evidence that oxygen production began in Earth's oceans at least 100 million years before the GOE, and goes a step further in demonstrating that even very low concentrations of oxygen can have profound effects on ocean chemistry.
To arrive at their results, the researchers analyzed 2.5 billion-year-old black shales from Western Australia. Essentially representing fossilized pieces of the ancient seafloor, the fine layers within the rocks allowed the researchers to page through ocean chemistry's evolving history.
Specifically, the shales revealed that episodes of hydrogen sulfide accumulation in the oxygen-free deep ocean occurred nearly 100 million years before the GOE and up to 700 millaion years earlier than such conditions were predicted by past models for the early ocean. Scientists have long believed that the early ocean, for more than half of Earth's 4.6 billion-year history, was characterized instead by high amounts of dissolved iron under conditions of essentially no oxygen.
More on this at:
http://www.astrobio.net/pressrelease/3297/a-new-wrinkle-in-ancient-ocean-chemistry
Two questions that remain unresolved in studies of the early Earth are when oxygen production via photosynthesis got started and when it began to alter the chemistry of Earth's ocean and atmosphere.
Now a research team led by geoscientists at the University of California, Riverside corroborates recent evidence that oxygen production began in Earth's oceans at least 100 million years before the GOE, and goes a step further in demonstrating that even very low concentrations of oxygen can have profound effects on ocean chemistry.
To arrive at their results, the researchers analyzed 2.5 billion-year-old black shales from Western Australia. Essentially representing fossilized pieces of the ancient seafloor, the fine layers within the rocks allowed the researchers to page through ocean chemistry's evolving history.
Specifically, the shales revealed that episodes of hydrogen sulfide accumulation in the oxygen-free deep ocean occurred nearly 100 million years before the GOE and up to 700 millaion years earlier than such conditions were predicted by past models for the early ocean. Scientists have long believed that the early ocean, for more than half of Earth's 4.6 billion-year history, was characterized instead by high amounts of dissolved iron under conditions of essentially no oxygen.
http://www.astrobio.net/pressrelease/3297/a-new-wrinkle-in-ancient-ocean-chemistry
African desert rift confirmed as new ocean in the making
Published: Monday, November 2, 2009 - 14:57 in Earth & Climate
In 2005, a gigantic, 35-mile-long rift broke open the desert ground in Ethiopia. At the time, some geologists believed the rift was the beginning of a new ocean as two parts of the African continent pulled apart, but the claim was controversial. Now, scientists from several countries have confirmed that the volcanic processes at work beneath the Ethiopian rift are nearly identical to those at the bottom of the world's oceans, and the rift is indeed likely the beginning of a new sea.
The new study, published in the latest issue of Geophysical Research Letters, suggests that the highly active volcanic boundaries along the edges of tectonic ocean plates may suddenly break apart in large sections, instead of little by little as has been predominantly believed. In addition, such sudden large-scale events on land pose a much more serious hazard to populations living near the rift than would several smaller events, says Cindy Ebinger, professor of earth and environmental sciences at the University of Rochester and co-author of the study.
"This work is a breakthrough in our understanding of continental rifting leading to the creation of new ocean basins," says Ken Macdonald, professor emeritus in the Department of Earth Science at the University of California, Santa Barbara, and who is not affiliated with the research. "For the first time they demonstrate that activity on one rift segment can trigger a major episode of magma injection and associated deformation on a neighboring segment. Careful study of the 2005 mega-dike intrusion and its aftermath will continue to provide extraordinary opportunities for learning about continental rifts and mid-ocean ridges."
"The whole point of this study is to learn whether what is happening in Ethiopia is like what is happening at the bottom of the ocean where it's almost impossible for us to go," says Ebinger. "We knew that if we could establish that, then Ethiopia would essentially be a unique and superb ocean-ridge laboratory for us. Because of the unprecedented cross-border collaboration behind this research, we now know that the answer is yes, it is analogous."
Atalay Ayele, professor at the Addis Ababa University in Ethiopia, led the investigation, painstakingly gathering seismic data surrounding the 2005 event that led to the giant rift opening more than 20 feet in width in just days. Along with the seismic information from Ethiopia, Ayele combined data from neighboring Eritrea with the help of Ghebrebrhan Ogubazghi, professor at the Eritrea Institute of Technology, and from Yemen with the help of Jamal Sholan of the National Yemen Seismological Observatory Center. The map he drew of when and where earthquakes happened in the region fit tremendously well with the more detailed analyses Ebinger has conducted in more recent years.
Ayele's reconstruction of events showed that the rift did not open in a series of small earthquakes over an extended period of time, but tore open along its entire 35-mile length in just days. A volcano called Dabbahu at the northern end of the rift erupted first, then magma pushed up through the middle of the rift area and began "unzipping" the rift in both directions, says Ebinger.
Since the 2005 event, Ebinger and her colleagues have installed seismometers and measured 12 similar—though dramatically less intense—events.
"We know that seafloor ridges are created by a similar intrusion of magma into a rift, but we never knew that a huge length of the ridge could break open at once like this," says Ebinger. She explains that since the areas where the seafloor is spreading are almost always situated under miles of ocean, it's nearly impossible to monitor more than a small section of the ridge at once so there's no way for geologists to know how much of the ridge may break open and spread at any one time. "Seafloor ridges are made up of sections, each of which can be hundreds of miles long. Because of this study, we now know that each one of those segments can tear open in a just a few days."
Ebinger and her colleagues are continuing to monitor the area in Ethiopia to learn more about how the magma system beneath the rift evolves as the rift continues to grow.
Source: University of Rochester
Link to this story: http://esciencenews.com/articles/2009/11/02/african.desert.rift.confirmed.new.ocean.making
In 2005, a gigantic, 35-mile-long rift broke open the desert ground in Ethiopia. At the time, some geologists believed the rift was the beginning of a new ocean as two parts of the African continent pulled apart, but the claim was controversial. Now, scientists from several countries have confirmed that the volcanic processes at work beneath the Ethiopian rift are nearly identical to those at the bottom of the world's oceans, and the rift is indeed likely the beginning of a new sea.
The new study, published in the latest issue of Geophysical Research Letters, suggests that the highly active volcanic boundaries along the edges of tectonic ocean plates may suddenly break apart in large sections, instead of little by little as has been predominantly believed. In addition, such sudden large-scale events on land pose a much more serious hazard to populations living near the rift than would several smaller events, says Cindy Ebinger, professor of earth and environmental sciences at the University of Rochester and co-author of the study.
"This work is a breakthrough in our understanding of continental rifting leading to the creation of new ocean basins," says Ken Macdonald, professor emeritus in the Department of Earth Science at the University of California, Santa Barbara, and who is not affiliated with the research. "For the first time they demonstrate that activity on one rift segment can trigger a major episode of magma injection and associated deformation on a neighboring segment. Careful study of the 2005 mega-dike intrusion and its aftermath will continue to provide extraordinary opportunities for learning about continental rifts and mid-ocean ridges."
"The whole point of this study is to learn whether what is happening in Ethiopia is like what is happening at the bottom of the ocean where it's almost impossible for us to go," says Ebinger. "We knew that if we could establish that, then Ethiopia would essentially be a unique and superb ocean-ridge laboratory for us. Because of the unprecedented cross-border collaboration behind this research, we now know that the answer is yes, it is analogous."
Atalay Ayele, professor at the Addis Ababa University in Ethiopia, led the investigation, painstakingly gathering seismic data surrounding the 2005 event that led to the giant rift opening more than 20 feet in width in just days. Along with the seismic information from Ethiopia, Ayele combined data from neighboring Eritrea with the help of Ghebrebrhan Ogubazghi, professor at the Eritrea Institute of Technology, and from Yemen with the help of Jamal Sholan of the National Yemen Seismological Observatory Center. The map he drew of when and where earthquakes happened in the region fit tremendously well with the more detailed analyses Ebinger has conducted in more recent years.
Ayele's reconstruction of events showed that the rift did not open in a series of small earthquakes over an extended period of time, but tore open along its entire 35-mile length in just days. A volcano called Dabbahu at the northern end of the rift erupted first, then magma pushed up through the middle of the rift area and began "unzipping" the rift in both directions, says Ebinger.
Since the 2005 event, Ebinger and her colleagues have installed seismometers and measured 12 similar—though dramatically less intense—events.
"We know that seafloor ridges are created by a similar intrusion of magma into a rift, but we never knew that a huge length of the ridge could break open at once like this," says Ebinger. She explains that since the areas where the seafloor is spreading are almost always situated under miles of ocean, it's nearly impossible to monitor more than a small section of the ridge at once so there's no way for geologists to know how much of the ridge may break open and spread at any one time. "Seafloor ridges are made up of sections, each of which can be hundreds of miles long. Because of this study, we now know that each one of those segments can tear open in a just a few days."
Ebinger and her colleagues are continuing to monitor the area in Ethiopia to learn more about how the magma system beneath the rift evolves as the rift continues to grow.
Source: University of Rochester
Link to this story: http://esciencenews.com/articles/2009/11/02/african.desert.rift.confirmed.new.ocean.making
VOLCANIC AND FERRIC SURPRISES ON MERCURY
New images from the MESSENGER spacecraft’s third trip past Mercury reveal some of the most recent volcanic activity on the planet’s surface, scientists reported during a press teleconference November 3.
The images are evidence of activity recent enough that planetary scientists may need to rethink the planet’s history. “It was thought that the internal geological activity on Mercury ended much earlier than on any other planet,” said Brett Denevi of Arizona State University. “We’re seeing that might not be the case.”
More on this story at http://www.sciencenews.org/view/generic/id/49071/title/Volcanic_and_ferric_surprises_on_Mercury
Friday, October 30, 2009
Volcanoes Played Role In Ancient Ice Age, Mass Extinction
Researchers here have discovered the pivotal role that volcanoes played in a deadly ice age 450 million years ago.
Perhaps ironically, these volcanoes first caused global warming -- by releasing massive amounts of carbon dioxide into the atmosphere.
When they stopped erupting, Earth’s climate was thrown off balance, and the ice age began.
The discovery underscores the importance of carbon in Earth’s climate today, said Matthew Saltzman, associate professor of earth sciences at Ohio State University.
The results will appear in the journal Geology, in a paper now available online.
Previously, Saltzman and his team linked this same ice age to the rise of the Appalachian Mountains. As the exposed rock weathered, chemical reactions pulled carbon from Earth’s atmosphere, causing a global cooling which ultimately killed two-thirds of all species on the planet.
Now the researchers have discovered the other half of the story: giant volcanoes that formed during the closing of the proto-Atlantic Ocean -- known as the Iapetus Ocean -- set the stage for the rise of the Appalachians and the ice age that followed.
“Our model shows that these Atlantic volcanoes were spewing carbon into the atmosphere at the same time the Appalachians were removing it,” Saltzman explained. “For nearly 10 million years, the climate was at a stalemate. Then the eruptions abruptly stopped, and atmospheric carbon levels fell well below what they were in the time before volcanism. That kicked off the ice age,” he said.
This is the first evidence that a decrease in carbon from volcanic degassing -- combined with continued weathering of the Appalachians -- caused the long-enigmatic glaciation and extinction in the Ordovician period.
Here is the picture the researchers have assembled: 460 million years ago, during the Ordovician, volcanoes along the margin of what is now the Atlantic Ocean spewed massive amounts carbon dioxide into the atmosphere, turning the world into a hothouse. Lava from those volcanoes eventually collided with North America to form the Appalachian Mountains.
Acid rain -- rich in carbon dioxide -- pelted the newly exposed Appalachian rock and wore it away. Chemical reactions trapped the carbon in the resulting sediment, which formed reefs in the vast seas that covered North America.
For about 10 million years, the volcanoes continued to add carbon to the atmosphere as the Appalachians removed it, so the hothouse conditions remained stable. Life flourished in the warm oceans, including abundant species of trilobites and brachiopods.
Then, 450 million years ago, the eruptions stopped. But the Appalachians continued weathering, and atmospheric carbon levels plummeted. The Earth swung from a hothouse to an icehouse.
By 445 million years ago, glaciers had covered the south pole on top of the supercontinent of Gondwana (which would eventually break apart to form the continents of the southern hemisphere). Two-thirds of all species had perished.
When they started this research, Saltzman and his team knew that Earth’s climate must have changed drastically at the end of the Ordovician. But they didn’t know for certain that volcanoes were the driving force, explained Seth Young, who did this research for his doctoral degree at Ohio State. He is now a postdoctoral researcher at Indiana University.
“This was not necessarily what we expected when we started investigating, but as we combined our data sources, the story began to fall into place,” Young said.
Using a computer model, they drew together measurements of isotopes of chemical elements -- including strontium from rocks in Nevada and neodymium from rocks in Virginia and Pennsylvania -- with measurements of volcanic ash beds in the same locations. Then they factored in temperature models developed by other researchers.
The ash deposits demonstrated when the volcanoes stopped erupting; the strontium levels indicated that large amounts of volcanic rock were being eroded and the sediment was flooding Earth’s oceans during this time; and the neodymium levels pinpointed the Appalachians as the source of the sediment.
The new findings mesh well with what scientists know about these ancient proto-Atlantic volcanoes, which are thought to have produced the largest eruptions in Earth’s history. They issued enough lava to form the Appalachians, enough ash to cover the far ends of the earth, and enough carbon to heat the globe. Atmospheric carbon levels grew 20 times higher than they are today.
This study shows that when those volcanoes stopped erupting, carbon levels dropped, and the climate swung dramatically back to cold. The timing coincides with today’s best estimates of temperature fluctuations in the Ordovician.
“The ash beds start building up at the same time the Appalachian weathering begins, but then the record of volcanism ends, and the temperature drops,” Saltzman said. “Knowing these details can help us understand how carbon in the atmosphere is changing Earth’s climate today.”
Next, the researchers will examine the role of the ancient volcanic ash more closely. While the ash was in the atmosphere -- before it settled around the globe -- it might have blotted out the sun, and cooled the earth somewhat. Saltzman and his team want to make some estimate of this short-term cooling effect to refine their computer model.
Meanwhile, Young is just starting to re-analyze the same rock samples, this time looking for a different isotope -- sulfur. This, he hopes, will offer clues to how much oxygen was in the oceans, and how that oxygen may have affected life in the Ordovician.
Other contributors to this work include Kenneth Foland, professor emeritus of earth sciences, and Jeff Linder, a research associate, both of Ohio State; and Lee Kump, professor of geosciences at Pennsylvania State University.
This research was partly supported by the National Science Foundation.
original story at http://www.redorbit.com/news/science/1775126/volcanoes_played_role_in_ancient_ice_age_mass_extinction/index.html
Perhaps ironically, these volcanoes first caused global warming -- by releasing massive amounts of carbon dioxide into the atmosphere.
When they stopped erupting, Earth’s climate was thrown off balance, and the ice age began.
The discovery underscores the importance of carbon in Earth’s climate today, said Matthew Saltzman, associate professor of earth sciences at Ohio State University.
The results will appear in the journal Geology, in a paper now available online.
Previously, Saltzman and his team linked this same ice age to the rise of the Appalachian Mountains. As the exposed rock weathered, chemical reactions pulled carbon from Earth’s atmosphere, causing a global cooling which ultimately killed two-thirds of all species on the planet.
Now the researchers have discovered the other half of the story: giant volcanoes that formed during the closing of the proto-Atlantic Ocean -- known as the Iapetus Ocean -- set the stage for the rise of the Appalachians and the ice age that followed.
“Our model shows that these Atlantic volcanoes were spewing carbon into the atmosphere at the same time the Appalachians were removing it,” Saltzman explained. “For nearly 10 million years, the climate was at a stalemate. Then the eruptions abruptly stopped, and atmospheric carbon levels fell well below what they were in the time before volcanism. That kicked off the ice age,” he said.
This is the first evidence that a decrease in carbon from volcanic degassing -- combined with continued weathering of the Appalachians -- caused the long-enigmatic glaciation and extinction in the Ordovician period.
Here is the picture the researchers have assembled: 460 million years ago, during the Ordovician, volcanoes along the margin of what is now the Atlantic Ocean spewed massive amounts carbon dioxide into the atmosphere, turning the world into a hothouse. Lava from those volcanoes eventually collided with North America to form the Appalachian Mountains.
Acid rain -- rich in carbon dioxide -- pelted the newly exposed Appalachian rock and wore it away. Chemical reactions trapped the carbon in the resulting sediment, which formed reefs in the vast seas that covered North America.
For about 10 million years, the volcanoes continued to add carbon to the atmosphere as the Appalachians removed it, so the hothouse conditions remained stable. Life flourished in the warm oceans, including abundant species of trilobites and brachiopods.
Then, 450 million years ago, the eruptions stopped. But the Appalachians continued weathering, and atmospheric carbon levels plummeted. The Earth swung from a hothouse to an icehouse.
By 445 million years ago, glaciers had covered the south pole on top of the supercontinent of Gondwana (which would eventually break apart to form the continents of the southern hemisphere). Two-thirds of all species had perished.
When they started this research, Saltzman and his team knew that Earth’s climate must have changed drastically at the end of the Ordovician. But they didn’t know for certain that volcanoes were the driving force, explained Seth Young, who did this research for his doctoral degree at Ohio State. He is now a postdoctoral researcher at Indiana University.
“This was not necessarily what we expected when we started investigating, but as we combined our data sources, the story began to fall into place,” Young said.
Using a computer model, they drew together measurements of isotopes of chemical elements -- including strontium from rocks in Nevada and neodymium from rocks in Virginia and Pennsylvania -- with measurements of volcanic ash beds in the same locations. Then they factored in temperature models developed by other researchers.
The ash deposits demonstrated when the volcanoes stopped erupting; the strontium levels indicated that large amounts of volcanic rock were being eroded and the sediment was flooding Earth’s oceans during this time; and the neodymium levels pinpointed the Appalachians as the source of the sediment.
The new findings mesh well with what scientists know about these ancient proto-Atlantic volcanoes, which are thought to have produced the largest eruptions in Earth’s history. They issued enough lava to form the Appalachians, enough ash to cover the far ends of the earth, and enough carbon to heat the globe. Atmospheric carbon levels grew 20 times higher than they are today.
This study shows that when those volcanoes stopped erupting, carbon levels dropped, and the climate swung dramatically back to cold. The timing coincides with today’s best estimates of temperature fluctuations in the Ordovician.
“The ash beds start building up at the same time the Appalachian weathering begins, but then the record of volcanism ends, and the temperature drops,” Saltzman said. “Knowing these details can help us understand how carbon in the atmosphere is changing Earth’s climate today.”
Next, the researchers will examine the role of the ancient volcanic ash more closely. While the ash was in the atmosphere -- before it settled around the globe -- it might have blotted out the sun, and cooled the earth somewhat. Saltzman and his team want to make some estimate of this short-term cooling effect to refine their computer model.
Meanwhile, Young is just starting to re-analyze the same rock samples, this time looking for a different isotope -- sulfur. This, he hopes, will offer clues to how much oxygen was in the oceans, and how that oxygen may have affected life in the Ordovician.
Other contributors to this work include Kenneth Foland, professor emeritus of earth sciences, and Jeff Linder, a research associate, both of Ohio State; and Lee Kump, professor of geosciences at Pennsylvania State University.
This research was partly supported by the National Science Foundation.
original story at http://www.redorbit.com/news/science/1775126/volcanoes_played_role_in_ancient_ice_age_mass_extinction/index.html
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