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TOPIC: Evolution of the atmosphere


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The Great Oxidation Event
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Oxygen, key to life on Earth today, began to appear on the planet millions of years earlier than scientists had thought, new research indicates.
An analysis of a deep rock core from Australia indicates the presence of at least some oxygen 50 million to 100 million years before the great change when the life-giving element began rising to today's levels, according to two papers appearing in Friday's edition of the journal Science.
Previously, the earliest indications of oxygen had been from between 2.3 billion and 2.4 billion years ago when the "Great Oxidation Event'' occurred.

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RE: Evolution of the atmosphere
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The history of life on Earth is closely linked to the appearance of oxygen in the atmosphere, which scientists think first occurred in significant amounts during a "Great Oxidation Event" some 2.4 billion years ago. However, until now little was known of environmental changes prior to this event. New findings by two teams of scientists - one led by geologists from the University of Maryland and the other by Arizona State researchers - indicate that significant oxidative changes were occurring in the oceans and atmosphere before the Great Oxidation Event.
The researchers analysed layers of sedimentary rock in a 3000 ft-long core sample from the Hamersley Basin in Western Australia and found evidence that a small but significant amount of oxygen was present in the oceans and possibly Earth's atmosphere 2.5 billion years ago. Their data also suggest that oxygen was nearly undetectable just before that time. Two papers outlining these findings will be published in the September 28 issue of the journal Science.

"Together, these papers provide compelling evidence for a shift in the oxidation state of the surface ocean 50 million years before the Great Oxidation Event. We believe that these findings are a significant step in our understanding of the oxygenation of Earth because they link changes in the environment with that of the biosphere" - Alan Jay Kaufman, Associate Professor of Geochemistry at the University of Maryland.

Kaufman and graduate student David Johnston led the Maryland research team, and Kaufman was also a member of the second Arizona State University team led by ASU biogeochemist Ariel Anbar. Also involved in the companion papers were scientists from the University of Washington, the University of California in Riverside and the University of Alberta. The work was supported by the Astrobiology Drilling Program of the NASA Astrobiology Institute and by the National Science Foundation, with logistical support from the Geological Survey of Western Australia.

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Determining the concentration of carbon dioxide in the ancient atmosphere remains a critical hurdle to understanding Earth surface temperatures, compositional changes in atmospheric chemistry, and the evolution of Earths earliest biosphere.

Kah and Riding report the finding of petrographic fabrics in 1.2-billion-year-old carbonate strata that suggest the process of cyanobacterial calcification. When ambient atmospheric partial pressure of CO2 (pCO2) concentrations fall below roughly 10 times present atmospheric levels (PAL), cyanobacteria begin to use a combination of dissolved carbonate species (CO32- and HCO3-) in the photosynthetic production of organic matter. The cyanobacteria, however, must perform a series of biochemical gymnastics to utilise HCO3- in this process. As a byproduct of these biochemical changes, the pH of the microbial sheath rises dramatically and induces the precipitation of calcium carbonate minerals. Identification of these calcified sheaths in the geologic record thus place an upper limit on pCO2. Atmospheric concentrations of CO2 <10 times PAL in the Mesoproterozoic are significantly lower than previous estimates, and indicate the requirement of additional greenhouse gasses, such as methane, in the atmosphere to keep the oceans from freezing.

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A switch from predominantly undersea volcanoes to a mix of undersea and terrestrial ones shifted the Earth's atmosphere from devoid of oxygen to one with free oxygen, according to geologists.

"The rise of oxygen allowed for the evolution of complex oxygen-breathing life forms"  -  Lee R. Kump, professor of geoscience, Penn State.

The change in Earth's atmosphere occurred about 2.5 billion years ago. And the bacteria theory has long been problematic, because fossilized cyanobacteria first appeared 200 million years earlier. Scientists wondered why they took so long to fill the atmosphere with oxygen. The answer appears to be that underwater volcanoes were undoing their work.
To put the story together, geoscientists Lee Kump of Pennsylvania State University in State College and Mark Barley of the University of Western Australia in Crawley relied on some recent clues. Improvements in radioactive isotope dating techniques have timed the influx of oxygen more precisely, and it coincides with the formation of most of the continents, 2.5 billion years ago. Kump and Barley suspected there might be a link.

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Earth's atmosphere 3.2 billion years ago
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The other day I was talking to a geologist friend of mine who told me about a pebble she found that held a clue to the amount of carbon dioxide in Earth's atmosphere 3.2 billion years ago.
The walnut-sized pebble, she explained, was found in a slender core sample drilled from a gold mine in South Africa its timeworn surface long ago weathered to a rind by running water. My geologist friend discovered that the pebble's crusty skin is made of quartz (like white beach sand) and iron-rich carbonate minerals.
The iron-rich carbonate is the clue. Carbonate contains a lot of carbon.

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L

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RE: Evolution of the atmosphere
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De skal dypere ned i urtiden. Forskerne Victor A. Melezhik og Aivo Lepland skal bore seg inn i 2,5 til 2 milliarder år gamle bergarter i Russland. De jakter på samspillet i de geologiske prosessene som skapte den "moderne Jorden".
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Two geologists from the Geological Survey of Norway (NGU), Victor A. Melezhik and Aivo Lepland, will drill into 2.5 to 2 billion year-old rocks in Russia to seek to understand the interaction between geological processes that created the modern Earth.

FAR-DEEP_Omr
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Map showing age of rock in drilling areas.
Credit: Geological Survey Of Norway


"This is a geological dream coming true" - Victor Melezhik.

For many years, this Norwegian-Russian geologist has been seeking a chance to study the depths of the Russian Precambrian layer.
Now hes getting started, along with his colleague at NGU, Aivo Lepland.
Six million NOK from the International Continental Drilling Programme (ICDP) are ready to be used to solve old geological riddles on the Kola Peninsula and the banks of Lake Onega in Karelia. Sediments and lavas dating from 2.5 to 2 billion years ago conceal valuable information, first and foremost about the oxygen content in the atmosphere which increased at that time.

"What really happened when the world got a more oxygen-rich atmosphere about 2.3 billion years ago? Was it because oxygen-producing life forms expanded? Or did geological evolution cause the Earths surface to become gradually more oxyic? That could have led to the production of oxygen exceeding its uptake, resulting in the excess oxygen accumulating in the atmosphere" - Aivo Lepland.

"We want to learn more about the fundamental processes behind the increase in oxygen. How long did it take and how did the various events interact and influence one another?" - Victor Melezhik.

The increase of oxygen in the atmosphere marked the very beginning of the modern Earth as it functions today. The rocks from the birth of the modern Earth have isotopic and chemical signatures that contain proof of dramatic events like the break-up of continents, volcanism and repeated global ice ages or the Snowball Earth.

"Increased biological production in the oceans led to deposition of sediments rich in plant remains. The first big oil reservoirs were also formed then. The asphalt-like oil that became fossilised long ago clearly shows that oil formed early in Earth history. Knowledge of the processes that formed this ancient oil may in turn point the way towards new plays and exploration techniques".

The drilling in the Fennoscandian Arctic Russia - Drilling Early Earth Project (FAR-DEEP) will take place from June to November this year. Fifteen holes from 100 to 500 metres deep will be drilled at Pechenga and Imandra on the Kola Peninsula and in Karelia, further south.
The actual research begins when Victor Melezhik and Aivo Lepland are back in Norway with 4000 metres of drill cores towards the end of the year. Scientists from as many as 15 nations will come to Trondheim then to sample the cores. Universities around the world have already promised more than 30 million NOK for this research, which will last five years.

"At the moment, only the recently started Centre for Geobiology at the University of Bergen has joined the project, but we want cooperation and contact with both the petroleum industry and other research institutions in Norway" - Aivo Lepland.

"Well also be building up a good, readily available archive of the material and the results so that everyone will be able to study the core samples, which we expect will be the best rock archive from the time when our oxygen-rich Earth evolved".

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L

Posts: 130179
Date:
Ancient Atmosphere
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Oxygen in Ancient Atmosphere Rose Gradually to Modern Levels:

The history of life on Earth is closely linked to the appearance of oxygen in the atmosphere. The current scientific consensus holds that significant amounts of oxygen first appeared in Earth's atmosphere some 2.4 billion years ago, with a second large increase in atmospheric oxygen occurring much later, perhaps around 600 million years ago.

However, new findings by University of Maryland geologists suggest that the second jump in atmospheric oxygen actually may have begun much earlier and occurred more gradually than previously thought. The findings were made possible using a new tool for tracking microbial life in ancient environments developed at Maryland. Funded by the National Science Foundation and NASA, the work appears in the December 2 issue of Science.

Graduate researcher David Johnston, research scientist Boswell Wing and colleagues in the University of Maryland's department of geology and Earth System Science Interdisciplinary Centre led an international team of researchers that used high-precision measurements of a rare sulphur isotope, 33S, to establish that ancient marine microbes known as sulphur disproportionating prokaryotes were widely active almost 500 million years earlier than previously thought.

The intermediate sulphur compounds used by these sulphur-disproportionating bacteria are formed by the exposure of sulphide minerals to oxygen gas. Thus, evidence of widespread activity by this type of bacteria has been interpreted by scientists as evidence of increased atmospheric oxygen content.

"These measurements imply that sulphur compound disproportionation was an active part of the sulphur cycle by [1.3 million years ago], and that progressive Earth surface oxygenation may have characterized the (middle Proterozoic)" .

The Proterozoic is the period in Earth's history from about 2.4 billion years ago to 545 million years ago.

"The findings also demonstrate that the new 33S-based research method can be used to uniquely track the presence and character of microbial life in ancient environments and provide a glimpse of evolution in action. This approach provides a significant new tool in the astrobiological search for early life on Earth and beyond" - David Johnston

When our planet formed some 4.5 billion years ago, virtually all the oxygen on Earth was chemically bound to other elements. It was in solid compounds like quartz and other silicate minerals, in liquid compounds like water, and in gaseous compounds like sulphur dioxide and carbon dioxide. Free oxygen -- the gas that allows us to breath, and which is essential to all advanced life -- was practically non-existent.

Scientists have long thought that appearance of oxygen in the atmosphere was marked by two distinct jumps in oxygen levels. In recent years, researchers have used a method developed by University of Maryland geologist James Farquhar and Maryland colleagues to conclusively determine that significant amounts of oxygen first appeared in Earth's atmosphere some 2.4 billion years ago. Sometimes referred to as the "Great Oxidation Event," this increase marks the beginning of the Proterozoic period.

A general scientific consensus has also held that the second major rise in atmospheric oxygen occurred some 600 million years ago, with oxygen rising to near modern levels at that time. Evidence of multicellular animals first appears in the geologic around this time.

"There has been a lot of discussion about whether the second major increase in atmospheric oxygen was quick and stepwise, or slow and progressive. Our results support the idea that the second rise was progressive and began around 1.3 billion years ago, rather than 0.6 billion years ago" - Boswell Wing.

In addition to Johnston, Wing's Maryland co-authors on the December 2 paper are geology colleagues James Farquhar and Jay Kaufman. Their group works to document links between sulphur isotopes and the evolution of Earth's atmosphere using a combination of field research, laboratory analysis of rock samples, geochemical models, photochemical experiments with sulphur-bearing gases and microbial experiments.

"Active microbial sulphur disproportionation in the Mesoproterozoic" by David T. Johnston, Boswell A. Wing, James Farquhar and Alan J. Kaufman, University of Maryland; Harald Strauss, Universität Münster; Timothy W. Lyons, University of California, Riverside; Linda C. Kah, University of Tennessee; Donald E. Canfield, Southern Denmark University: Science, Dec. 2, 2005.

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L

Posts: 130179
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RE: Ozone Hole
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British researchers from the University of Sheffield have hit on a clever way to search for ancient ozone holes and their relationship to mass extinctions: measure the remains of ultraviolet-B absorbing pigments ancient plants left in their fossilized spores and pollen.

To develop the approach, researcher Barry Lomax and his colleagues analysed spores held in the British Antarctic Survey's collection from South Georgia Island, a UK territory in the far south-western corner of the Atlantic Ocean. They discovered that since the 1960s, spores from living land plants have shown a three-fold increase in the concentration of UV-B absorbing pigments to protect themselves against a 14 percent decrease in stratospheric ozone.



"We have initially been investigating whether plants of palaeobotanical significance are capable of adapting to changes in UV-B radiation" - Barry Lomax.
In particular, they studied the UV-B response of the club moss Lycopodium magellanicum, a native of South Georgia Island.

"Now that this has been established we are investigating possible changes in terrestrial UV-B flux during the Permian-Triassic boundary (251 million years ago)" - Barry Lomax.

That boundary marks the largest mass extinction in the Earth's history and also coincides with the largest known eruption of lava and potentially ozone-destroying gases - the Siberian Traps.

The latest results from the ongoing work were presented by Lomax on Wednesday, 10 August, at Earth System Processes 2, a meeting co-convened by the Geological Society and Geological Association of Canada this week in Calgary, Alberta, Canada.

The modern increase in UV-B at South Georgia is the direct result of high latitude springtime ozone destruction in the stratosphere caused by decades of releases of human-made chlorofluorocarbons (CFCs). The situation may have been the same a quarter billion years ago, except that the earlier ozone-destroying chemicals came from the Earth itself.

"Volcanic eruptions can emit gases such as chlorine and bromine that are capable of destroying ozone" - Barry Lomax.
The heating of rocks near volcanic flows of the Siberian Traps may also release a wide range of organohalogens thought to be harmful to ozone.

The next step is to search for the chemical remains of the plant pigments in fossilized spores and pollen.
"The pigments break down to form compounds that are stable over geological time, so providing samples have not been subjected to large amounts of heat, the signature should be preserved"

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L

Posts: 130179
Date:
Evolution of the atmosphere
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The President of the Mineralogical Society of America, Douglas Rumble, III, of the Carnegie Institution's Geophysical Laboratory, describes new techniques, used on minerals, to reveal the steps that led to evolution of the atmosphere on Earth.
"Rocks, fossils, and other natural relics hold clues to ancient environments in the form of different ratios of isotopes--atomic variants of elements with the same number of protons but different numbers of neutrons.
Seawater, rain water, oxygen, and ozone, for instance, all have different ratios, or fingerprints, of the oxygen isotopes 16O, 17O, and 18O. Weathering, ground water, and direct deposition of atmospheric aerosols change the ratios of the isotopes in a rock revealing a lot about the past climate
."
Geochemists, mineralogists, and petrologists are studying anomalies of isotopes of oxygen and sulphur to piece together what happened to our atmosphere from about 3.9 billion years ago, when the crust of our planet was just forming and there was no oxygen in the atmosphere, to a primitive oxygenated world 2.3 billion years ago, and then to the present.
Scientists who have analysed surface minerals from all over the globe, used rockets and balloons to sample the stratosphere, collected and studied ice cores from Antarctica, conducted lab experiments, and run mathematical models, show that ultraviolet (UV) light from the Sun is an important driving force in atmospheric evolution.
Solar UV photons break up molecular oxygen (O2) to produced ozone (O3) leaving a tell-tale isotopic signature of excess 17O. The ozone layer began to form as the atmosphere gained oxygen, and has since shielded our planet from harmful solar rays and made life possible on Earth's surface.

The discovery of isotope anomalies, where none were previously suspected, adds a new tool to research on the relationships between shifts in atmospheric chemistry and climate change. Detailed studies of polar-ice cores and exposed deposits in Antarctic dry valleys may improve our understanding of the history of the ozone hole.


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