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TOPIC: Evolution of the atmosphere


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An ancient 'Great Leap Forward' for life in the open ocean

Plankton in the Earth's oceans received a huge boost when microorganisms capable of creating soluble nitrogen 'fertilizer' directly from the atmosphere diversified and spread throughout the open ocean. This event occurred at around 800 million years ago and it changed forever how carbon was cycled in the ocean.
It has long been believed that the appearance of complex multicellular life towards the end of the Precambrian (the geologic interval lasting up until 541 million years ago) was facilitated by an increase in oxygen, as revealed in the geological record. However, it has remained a mystery as to why oxygen increased at this particular time and what its relationship was to 'Snowball Earth' - the most extreme climatic changes the Earth has ever experienced - which were also taking place around then.

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The Ups and Downs of Early Atmospheric Oxygen

UC Riverside research team challenges conventional view of a simple two-step rise in early oxygen on Earth; study suggests instead dynamic oxygen concentrations that rose and fell over billions of years
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Ancient soils provide early whiff of oxygen

Oxygen may have been accumulating in Earth's atmosphere hundreds of millions of years earlier than we thought.
An international team has made the claim in Nature magazine after studying the oldest soils on Earth.
The researchers say elements in the three-billion-year-old material show evidence for oxidative weathering.

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An Oxygen-poor 'Boring' Ocean Challenged Evolution of Early Life

áA research team led by biogeochemists at the University of California, Riverside has filled in a billion-year gap in our understanding of conditions in the early ocean during a critical time in the history of life on Earth.
It is now well accepted that appreciable oxygen first accumulated in the atmosphere about 2.4 to 2.3 billion years ago. It is equally well accepted that the build-up of oxygen in the ocean may have lagged the atmospheric increase by well over a billion years, but the details of those conditions have long been elusive because of the patchiness of the ancient rock record.

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Great Oxidation Event
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Great Oxidation Event: More oxygen through multicellularity

The appearance of free oxygen in the Earth's atmosphere led to the Great Oxidation Event. This was triggered by cyanobacteria producing the oxygen which developed into multicellular forms as early as 2.3 billion years ago. As evolutionary biologists from the Universities of Zurich and Gothenburg have shown, this multicellularity was linked to the rise in oxygen and thus played a significant role for life on Earth as it is today.
Cyanobacteria belong to the Earth's oldest organisms. They are still present today in oceans and waters and even in hot springs. By producing oxygen and evolving into multicellular forms, they played a key role in the emergence of organisms that breathe oxygen. This has, now, been demonstrated by a team of scientists under the supervision and instruction of evolutionary biologists from the University of Zurich. According to their studies, cyanobacteria developed multicellularity around one billion years earlier than eukaryotes - cells with one true nucleus. At almost the same time as multicellular cyanobacteria appeared, a process of oxygenation began in the oceans and in the Earth's atmosphere.

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Geological record shows air up there came from below

The influence of the ground beneath us on the air around us could be greater than scientists had previously thought, according to new research that links the long-ago proliferation of oxygen in Earth's atmosphere to a sudden change in the inner workings of our planet.
Princeton University researchers report in the journal Nature that rocks preserved in the Earth's crust reveal that a steep decline in the intensity of melting within the planet's mantle - the hot, heat-transferring rock layer between the crust and molten outer core - brought about ideal conditions for the period known as the Great Oxygenation Event (GOE) that occurred roughly 2.5 billion years ago.

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Title: Rethinking the Paleoproterozoic Great Oxidation Event: A Biological Perspective
Authors: John W. Grula (Observatories of the Carnegie Institution for Science, Pasadena, CA, USA)

Competing geophysical/geochemical hypotheses for how Earth's surface became oxygenated - organic carbon burial, hydrogen escape to space, and changes in the redox state of volcanic gases - are examined and a more biologically-based hypothesis is offered in response. It is argued that organic carbon burial is of minor importance to the accumulation of oxygen in a mainly anoxic world where aerobic respiration is not globally significant. Thus, for the Great Oxidation Event (GOE) ~ 2.4 Gyr ago, an increasing flux of O2 due to its production by an expanding population of cyanobacteria is parameterised as the primary source of O2. Various factors would have constrained cyanobacterial proliferation and O2 production during most of the Archean and therefore a long delay between the appearance of cyanobacteria and oxygenation of the atmosphere is to be expected. Destruction of O2 via CH4 oxidation in the atmosphere was a major O2 sink during the Archean, and the GOE is explained to a significant extent by a large decline in the methanogen population and corresponding CH4 flux which, in turn, was caused primarily by partial oxygenation of the surface ocean. The partially oxygenated state of these waters also made it possible for an aerobic methanotroph population to become established. This further contributed to the large reduction in the CH4 flux to the atmosphere by increasing the consumption of CH4 diffusing upwards from the deeper anoxic depths of the water column as well as any CH4 still being produced in the upper layer. The reduction in the CH4 flux lowered the CH4 oxidation sink for O2 at about the same time the metamorphic and volcanic gas sinks for O2 also declined. As the O2 source increased from an expanding population of cyanobacteria - triggered by a burst of continent formation ~ 2.7-2.4 Gyr ago - the atmosphere flipped and became permanently oxygenated.

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á Early Earth's atmosphere clear and cloudy

Ancient rocks indicate early Earth regularly flipped between an oxygen-rich atmosphere and a thick hydrocarbon haze like Saturn's moon Titan.
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Title: Protein Domain Structure Uncovers the Origin of Aerobic Metabolism and the Rise of Planetary Oxygen
Authors: Kyung Mo Kim, Tao Qin, Ying-Ying Jiang, Ling-Ling Chen, Min Xiong, Derek Caetano-AnollÚs, Hong-Yu Zhang, Gustavo Caetano-AnollÚs

The origin and evolution of modern biochemistry remain a mystery despite advances in evolutionary bioinformatics. Here, we use a structural census in nearly 1,000 genomes and a molecular clock of folds to define a timeline of appearance of protein families linked to single-domain enzymes. The timeline sorts out enzymatic recruitment, validates patterns in metabolic history, and reveals that the most ancient reaction of aerobic metabolism involved the synthesis of pyridoxal 5'-phosphate or pyridoxal and appeared 2.9 Gyr ago. The oxygen source for this primordial reaction was probably Mn catalase, which appeared at the same time and could have generated oxygen as a side product of hydrogen peroxide detoxification. Finally, evolutionary analysis of transferred groups and metabolite fragments revealed that oxidised sulphur did not participate in metabolism until the rise of oxygen. The evolutionary patterns we uncover in molecules and chemistries provide strong support for the coevolution of biochemistry and geochemistry.

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Great Oxidation Event
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New research shows evidence of early oxygen on our planet.

Today, oxygen takes up a hefty portion of Earth's atmosphere: Life-sustaining O2 molecules make up 21 percent of the air we breathe. However, very early in Earth's history, O2 was a rare - if not completely absent - player in the turbulent mix of primordial gases. It wasn't until the "Great Oxidation Event" (GOE), nearly 2.3 billion years ago, when oxygen made any measurable dent in the atmosphere, stimulating the evolution of air-breathing organisms and, ultimately, complex life as we know it today.
Now, new research from MIT suggests O2 may have been made on Earth hundreds of millions of years before its debut in the atmosphere, keeping a low profile in "oxygen oases" in the oceans. The MIT researchers found evidence that tiny aerobic organisms may have evolved to survive on extremely low levels of the gas in these undersea oases.

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