Origin Of 'Breathable' Atmosphere Half A Billion Years Ago Discovered

Source:

http://www.sciencedaily.com/releases/2007/10/071029094320.htm

ScienceDaily (Oct. 30, 2007) — Ohio State University geologists and their colleagues have uncovered evidence of when Earth may have first supported an oxygen-rich atmosphere similar to the one we breathe today.

The study suggests that upheavals in the earth's crust initiated a kind of reverse-greenhouse effect 500 million years ago that cooled the world's oceans, spawned giant plankton blooms, and sent a burst of oxygen into the atmosphere.
That oxygen may have helped trigger one of the largest growths of biodiversity in Earth's history.
Matthew Saltzman, associate professor of earth sciences at Ohio State, reported the findings October 28 at the meeting of the Geological Society of America in Denver.
For a decade, he and his team have been assembling evidence of climate change that occurred 500 million years ago, during the late Cambrian period. They measured the amounts of different chemicals in rock cores taken from around the world, to piece together a complex chain of events from the period.
Their latest measurements, taken in cores from the central United States and the Australian outback, revealed new evidence of a geologic event called the Steptoean Positive Carbon Isotope Excursion (SPICE).
Amounts of carbon and sulfur in the rocks suggest that the event dramatically cooled Earth's climate over two million years -- a very short time by geologic standards. Before the event, the Earth was a hothouse, with up to 20 times more carbon dioxide in the atmosphere compared to the present day. Afterward, the planet had cooled and the carbon dioxide had been replaced with oxygen. The climate and atmospheric composition would have been similar to today.
“If we could go back in time and walk around in the late Cambrian, this seems to be the first time we would have felt at home,” Saltzman said. “Of course, there was no life on land at the time, so it wouldn't have been all that comfortable.”
The land was devoid of plants and animals, but there was life in the ocean, mainly in the form of plankton, sea sponges, and trilobites. Most of the early ancestors of the plants and animals we know today existed during the Cambrian, but life wasn't very diverse.
Then, during the Ordovician period, which began around 490 million years ago, many new species sprang into being. The first coral reefs formed during that time, and the first true fish swam among them. New plants evolved and began colonizing land.
“If you picture the evolutionary ‘tree of life,' most of the main branches existed during the Cambrian, but most of the smaller branches didn't get filled in until the Ordovician,” Saltzman said. “That's when animal life really began to develop at the family and genus level.” Researchers call this diversification the “Ordovician radiation.”
The composition of the atmosphere has changed many times since, but the pace of change during the Cambrian is remarkable. That's why Saltzman and his colleagues refer to this sudden influx of oxygen during the SPICE event as a “pulse” or “burst.”
“After this pulse of oxygen, the world remained in an essentially stable, warm climate, until late in the Ordovician,” Saltzman said.
He stopped short of saying that the oxygen-rich atmosphere caused the Ordovician radiation.
“We know that oxygen was released during the SPICE event, and we know that it persisted in the atmosphere for millions of years -- during the time of the Ordovician radiation -- so the timelines appear to match up. But to say that the SPICE event triggered the diversification is tricky, because it's hard to tell exactly when the diversification started,” he said.
“We would need to work with paleobiologists who understand how increased oxygen levels could have led to a diversification. Linking the two events precisely in time is always going to be difficult, but if we could link them conceptually, then it would become a more convincing story.”
Researchers have been trying to understand the sudden climate change during the Cambrian period ever since Saltzman found the first evidence of the SPICE event in rock in the American west in 1998. Later, rock from a site in Europe bolstered his hypothesis, but these latest finds in central Iowa and Queensland, Australia, prove that the SPICE event occurred worldwide.
During the Cambrian period, most of the continents as we know them today were either underwater or part of the Gondwana supercontinent, Saltzman explained. Tectonic activity was pushing new rock to the surface, where it was immediately eaten away by acid rain. Such chemical weathering pulls carbon dioxide from the air, traps the carbon in sediments, and releases oxygen -- a kind of greenhouse effect in reverse.
“From our previous work, we knew that carbon was captured and oxygen was released during the SPICE event, but we didn't know for sure that the oxygen stayed in the atmosphere,” Saltzman said.
They compared measurements of inorganic carbon -- captured during weathering -- with organic carbon -- produced by plankton during photosynthesis. And because plankton contain different ratios of the isotopes of carbon depending on the amount of oxygen in the air, the geologists were able to double-check their estimates of how much oxygen was released during the period, and how long it stayed in the atmosphere.
They also studied isotopes of sulfur, to determine whether much of the oxygen being produced was re-captured by sediments.
It wasn't.
Saltzman explained the chain of events this way: Tectonic activity led to increased weathering, which pulled carbon dioxide from the air and cooled the climate. Then, as the oceans cooled to more hospitable temperatures, the plankton prospered -- and in turn created more oxygen through photosynthesis.
“It was a double whammy,” he said. “There's really no way around it when we combine the carbon and sulfur isotope data -- oxygen levels dramatically rose during that time.”
What can this event tell us about climate change today? “Oxygen levels have been stable for the last 50 million years, but they have fluctuated over the last 500 million,” Saltzman said. “We showed that the oxygen burst in the late Cambrian happened over only two million years, so that is an indication of the sensitivity of the carbon cycle and how fast things can change.”
Global cooling may have boosted life early in the Ordovician period, but around 450 million years ago, more tectonic activity -- most likely, the rise of the Appalachian Mountains -- brought on a deadly ice age. So while most of the world's plant and animal species were born during the Ordovician period, by the end of it, more than half of them had gone extinct.
Coauthors on this study included Seth Young, a graduate student in earth sciences at Ohio State; Ben Gill, a graduate student, and Tim Lyons, professor of earth sciences, both at the University of California, Riverside; Lee Kump, professor of geosciences at Penn State University; and Bruce Runnegar, professor of paleontology at the University of California, Los Angeles.
Adapted from materials provided by Ohio State University.

Fausto Intilla

www.oloscience.com

Geologists Recover Rocks Yielding Unprecedented Insights Into San Andreas Fault

Source:

http://www.sciencedaily.com/releases/2007/10/071004143120.htm

Science Daily — For the first time, geologists have extracted intact rock samples from 2 miles beneath the surface of the San Andreas Fault, the infamous rupture that runs 800 miles along the length of California.

Never before have scientists had available for study rock samples from deep inside one of the actively moving tectonic plate-bounding faults responsible for the world's most damaging earthquakes. Now, with this newly recovered material, scientists hope to answer long-standing questions about the fault's composition and properties.
Altogether, the geologists retrieved 135 feet of 4-inch diameter rock cores weighing roughly 1 ton. They were brought to the surface through a research borehole drilled more than 2.5 miles into the Earth. The last of the cores was brought to the surface in the predawn hours of Sept. 7.
Scientists seeking to understand how the great faults bounding Earth's vast tectonic plates evolve and generate earthquakes have always had to infer the processes through indirect means. Up until now, they could only work with samples of ancient faults exposed at the Earth's surface after millions of years of erosion and uplift, together with computer simulations and laboratory experiments approximating what they think might be happening at the depths at which earthquakes occur.
"Now we can hold the San Andreas Fault in our hands," said Mark Zoback, the Benjamin M. Page Professor in Earth Sciences at Stanford. "We know what it's made of. We can study how it works."
Zoback is one of three co-principal investigators of the San Andreas Fault Observatory at Depth (SAFOD) project, which is establishing the world's first underground earthquake observatory. William Ellsworth and Steve Hickman, geophysicists with the U.S. Geological Survey (USGS) in Menlo Park, Calif., are the other co-principal investigators.
SAFOD, which first broke ground in 2004, is a major research component of EarthScope, a National Science Foundation-funded program being carried out in collaboration with the USGS and NASA to investigate the forces that shape the North American continent and the physical processes controlling earthquakes and volcanic eruptions.
"This is tremendously exciting. Obtaining cores from the actively slipping San Andreas Fault is truly unprecedented and will allow truly transformative research and discoveries," said Kaye Shedlock, EarthScope program director at the National Science Foundation.
In the next phase of the experiment, the science team will install an array of seismic instruments in the 2.5-mile-long borehole that runs from the Pacific plate on the west side of the fault into the North American plate on the east. By placing sensors next to a zone that has been the source of many small temblors, scientists will be able to observe the earthquake generation process with unprecedented acuity. They hope to keep the observatory operating for the next 10 to 20 years.
Studying the San Andreas Fault is important because, as Zoback noted, "The really big earthquakes occur on plate boundaries like the San Andreas Fault." The SAFOD site, located about 23 miles northeast of Paso Robles near the tiny town of Parkfield, sits on a particularly active section of the fault that moves regularly. But it does not produce large earthquakes. Instead, it moves in modest increments by a process called creep, in which the two sides of the fault slide slowly past one another, accompanied by occasional small quakes, most of which are not even felt at the surface.
One of the big questions the researchers seek to answer is how, when most of the fault moves in violent, episodic upheavals, can there be a section where the same massive tectonic plates seem, by comparison, to gently tiptoe past each other with the delicate tread of little cat feet"
"There have been many theories about why the San Andreas Fault slides along so easily, none of which could be tested directly until now," Hickman said. Some posit the presence of especially slippery clays, called smectites. Others suggest there may be high water pressure along the fault plane lubricating the surface. Still others note the presence of a mineral called serpentine exposed in several places along the surface trace of the fault, which-if it existed at depth-could both weaken the fault and cause it to creep.
Zoback said the correlation between the occurrence of serpentine, a metamorphosed remnant of old oceanic crust, and the slippery nature of the fault motion in the area has been the subject of speculation for more than 40 years. However, it has never been demonstrated that serpentine actually occurs along the active San Andreas at depth, and the mechanism by which serpentine might limber up the fault was unknown.
Then, in 2005, when the SAFOD drill pierced the zone of active faulting using rotary drilling (which grinds up the rock into tiny fragments), mineralogist Diane Moore of the USGS detected talc in the rock cuttings brought up to the surface. This finding was published in the Aug. 16, 2007, issue of Nature.
"Talc is one of the slipperiest, weakest minerals ever studied," Hickman said.
Might the same mineral that helps keep a baby's bottom smooth also be smoothing the way for the huge tectonic plates" Chemically, it's possible, for when serpentine is subjected to high temperatures in the presence of water containing silica, it forms talc.
Serpentine might also control how faults behave in other ways. "Serpentine can dissolve in ground water as fault particles grind past each other and then crystallize in nearby open pore spaces, allowing the fault to creep even under very little pressure," Hickman said.
The SAFOD borehole cored into two active traces of the fault this summer, both contained within a broad fault "zone" about 700 feet wide. The deeper of the two active fault zones, designated 10830 for its distance in feet from the surface as measured along the curving borehole, yielded an 8-foot-long section of very fine-grained powder called fault gouge. Such gouge is common in fault zones and is produced by the grinding of rock against rock. "What is remarkable about this gouge is that it contains abundant fragments of serpentine that appear to have been swept up into the gouge from the adjacent solid rock," Hickman said. "The serpentine is floating around in the fault gouge like raisins in raisin pudding."
The only way to know what role serpentine, talc or other exotic minerals play in controlling the behavior of the San Andreas Fault is to study the SAFOD core samples in the laboratory.
"To an earthquake scientist, these cores are like the Apollo moon rocks," Hickman said. "Scientists from around the world are anxious to get their hands on them in the hope that they can help solve the mystery of how this major, active plate boundary works."
Will these new samples allow scientists to predict earthquakes" The short answer is no. But research on these samples could provide clues to answer the question of whether earthquakes are predictable. The observatory will allow scientists to begin to address whether there are precursory phenomena occurring within the fault zone.
The other fault zone, called 10480, contains 3 feet of fault gouge. It also produces small earthquakes at a location about 300 feet below the borehole. "Remarkably, we observe the same earthquake rupturing at the same spot on the fault year after year," Ellsworth said. This repeating earthquake, always about a magnitude 2, will be the focus of the observatory to be installed inside the fault in 2008.
Sensitive seismometers and tiltmeters to be installed in the SAFOD borehole directly above the spot that ruptures will observe for the first time the birthing process of an earthquake from the zone where the earthquake energy accumulates. Preliminary observations made in 2006 already have revealed the tiniest earthquakes ever observed-so small they have negative magnitudes.
In early December, a "sample party" will be held at the USGS office in Menlo Park, where the cores will be on display and scientists will offer their proposals to do research projects in a bid to be allowed to analyze part of the core.
Zoback said most of the initial testing will be nondestructive in order to preserve the samples for as long as possible. "But then, some of the material will be made available for testing that simulates earthquakes and fault slip in the lab," he said.
When not being examined, the core samples will be refrigerated and kept moist to prevent the cores and the fluid in them from being disturbed.
Some of the cores will be on display at the press conference to be held Oct. 4 at Stanford University in Tresidder Union's Oak Room.
In addition to funding from the National Science Foundation, USGS and Stanford University, the SAFOD project also has been supported financially by the International Continental Scientific Drilling Program.
Note: This story has been adapted from material provided by Stanford University.

Fausto Intilla

www.oloscience.com

Devastating Earthquake May Threaten Middle East's Near Future, Geologist Predicts

Source:

http://www.sciencedaily.com/releases/2007/10/071003142432.htm

Science Daily — The best seismologists in the world don’t know when the next big earthquake will hit. But a Tel Aviv University geologist suggests that earthquake patterns recorded in historical documents of Middle Eastern countries indicate that the region’s next significant quake is long overdue.

A major quake of magnitude seven on the Richter scale in the politically-fragile region of the Middle East could have dire consequences for precious holy sites and even world peace, says Tel Aviv University geologist Dr. Shmulik Marco. In light of this imminent danger, Marco, from the school’s Department of Geophysics and Planetary Sciences, has taken an historical approach to earthquake forecasting by using ancient records from the Vatican and other religious sources in his assessment. The past holds the key to the future, he says.
“All of us in the region should be worried,” explains Marco, who dedicates his career to piecing together ancient clues.
Based on the translations of hundreds of documents -- some of the originals of which he assumes reside in Vatican vaults -- Marco has helped determine that a series of devastating earthquakes have hit the Holy Land over the last two thousand years. The major ones were recorded along the Jordan Valley in the years 31 B.C.E., 363 C.E., 749 C.E., and 1033 C.E. “So roughly,” warns Marco, “we are talking about an interval of every 400 years. If we follow the patterns of nature, a major quake should be expected any time because almost a whole millennium has passed since the last strong earthquake of 1033.”
Written by monks and clergy, the documents, which span about two millenia, can help determine the location and impact of future quakes on several fault planes cutting through Israel and its neighboring countries, Marco believes. “We use the records, written in churches and monasteries or by hermits in the desert, to find patterns,” he says. Marco credits the help of an international team of historians, who have deciphered the Latin, Greek, and Arabic of the original correspondence.
He continues, “Even if these papers were not ‘officially’ recording history, they hold a lot of information. ... Some are letters to Europe asking for funding of church repairs. And while many of these accounts are told in an archaic religious manner, they help us confirm the dates and location of major calamities. Following these patterns in the past can be a good predictor of the future.”
One of the most cited Christian chroniclers in history upon whom Marco bases some of his conclusions is a ninth-century Byzantine aristocratic monk named Theophanes, venerated today by Catholics. In one manuscript, Theophanes wrote, “A great earthquake in Palestine, by the Jordan and in all of Syria on 18 January in the 4th hour. Numberless multitudes perished, churches and monasteries collapsed especially in the desert of the Holy City.”
While Christian sources helped Marco confirm ancient catastrophes and cast light on future ones, Jewish sources from the Bible also gave him small pieces of the puzzle. A verse in Zachariah (Ch. 14) describes two instances of earthquakes, one of which split apart the Mount of Olives, he says. Muslim clergy have also collected ancient correspondence, which further broadens the picture.
”Earthquakes are a manifestation of deeper processes inside the earth,” Marco says. “My questions and analysis examine how often they occur and whether there is pattern to them, temporally or spatially. I am looking for patterns and I can say that based on ancient records, the pattern in Israel around the Dead Sea region is the most disturbing to us.
“When it strikes and it will this quake will affect Amman, Jordan as well as Ramallah, Bethlehem, and Jerusalem. Earthquakes don’t care about religion or political boundaries,” Marco concludes.
Note: This story has been adapted from material provided by Tel Aviv University.

Fausto Intilla

www.oloscience.com

Carbon Dioxide Did Not End The Last Ice Age, Study Says

Source:

http://www.sciencedaily.com/releases/2007/09/070927154905.htm

Science Daily — Carbon dioxide did not cause the end of the last ice age, a new study in Science suggests, contrary to past inferences from ice core records.

"There has been this continual reference to the correspondence between CO2 and climate change as reflected in ice core records as justification for the role of CO2 in climate change," said USC geologist Lowell Stott, lead author of the study, slated for advance online publication Sept. 27 in Science Express.
"You can no longer argue that CO2 alone caused the end of the ice ages."
Deep-sea temperatures warmed about 1,300 years before the tropical surface ocean and well before the rise in atmospheric CO2, the study found. The finding suggests the rise in greenhouse gas was likely a result of warming and may have accelerated the meltdown -- but was not its main cause.
The study does not question the fact that CO2 plays a key role in climate.
"I don't want anyone to leave thinking that this is evidence that CO2 doesn't affect climate," Stott cautioned. "It does, but the important point is that CO2 is not the beginning and end of climate change."
While an increase in atmospheric CO2 and the end of the ice ages occurred at roughly the same time, scientists have debated whether CO2 caused the warming or was released later by an already warming sea.
The best estimate from other studies of when CO2 began to rise is no earlier than 18,000 years ago. Yet this study shows that the deep sea, which reflects oceanic temperature trends, started warming about 19,000 years ago.
"What this means is that a lot of energy went into the ocean long before the rise in atmospheric CO2," Stott said.
But where did this energy come from" Evidence pointed southward.
Water's salinity and temperature are properties that can be used to trace its origin -- and the warming deep water appeared to come from the Antarctic Ocean, the scientists wrote.
This water then was transported northward over 1,000 years via well-known deep-sea currents, a conclusion supported by carbon-dating evidence.
In addition, the researchers noted that deep-sea temperature increases coincided with the retreat of Antarctic sea ice, both occurring 19,000 years ago, before the northern hemisphere's ice retreat began.
Finally, Stott and colleagues found a correlation between melting Antarctic sea ice and increased springtime solar radiation over Antarctica, suggesting this might be the energy source.
As the sun pumped in heat, the warming accelerated because of sea-ice albedo feedbacks, in which retreating ice exposes ocean water that reflects less light and absorbs more heat, much like a dark T-shirt on a hot day.
In addition, the authors' model showed how changed ocean conditions may have been responsible for the release of CO2 from the ocean into the atmosphere, also accelerating the warming.
The link between the sun and ice age cycles is not new. The theory of Milankovitch cycles states that periodic changes in Earth's orbit cause increased summertime sun radiation in the northern hemisphere, which controls ice size.
However, this study suggests that the pace-keeper of ice sheet growth and retreat lies in the southern hemisphere's spring rather than the northern hemisphere's summer.
The conclusions also underscore the importance of regional climate dynamics, Stott said. "Here is an example of how a regional climate response translated into a global climate change," he explained.
Stott and colleagues arrived at their results by studying a unique sediment core from the western Pacific composed of fossilized surface-dwelling (planktonic) and bottom-dwelling (benthic) organisms.
These organisms -- foraminifera -- incorporate different isotopes of oxygen from ocean water into their calcite shells, depending on the temperature. By measuring the change in these isotopes in shells of different ages, it is possible to reconstruct how the deep and surface ocean temperatures changed through time.
If CO2 caused the warming, one would expect surface temperatures to increase before deep-sea temperatures, since the heat slowly would spread from top to bottom. Instead, carbon-dating showed that the water used by the bottom-dwelling organisms began warming about 1,300 years before the water used by surface-dwelling ones, suggesting that the warming spread bottom-up instead.
"The climate dynamic is much more complex than simply saying that CO2 rises and the temperature warms," Stott said. The complexities "have to be understood in order to appreciate how the climate system has changed in the past and how it will change in the future."
Stott's collaborators were Axel Timmermann of the University of Hawaii and Robert Thunell of the University of South Carolina. Stott was supported by the National Science Foundation and Timmerman by the International Pacific Research Center.
Stott is an expert in paleoclimatology and was a reviewer for the Intergovernmental Panel on Climate Change. He also recently co-authored a paper in Geophysical Research Letters tracing a 900-year history of monsoon variability in India.
The study, which analyzed isotopes in cave stalagmites, found correlations between recorded famines and monsoon failures, and found that some past monsoon failures appear to have lasted much longer than those that occurred during recorded history. The ongoing research is aimed at shedding light on the monsoon's poorly understood but vital role in Earth's climate.
Note: This story has been adapted from material provided by University of Southern California.

Fausto Intilla

www.oloscience.com