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TOPIC: Evolution of the atmosphere


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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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Plankton key to origin of Earth's first breathable atmosphere

Researchers studying the origin of Earth's first breathable atmosphere have zeroed in on the major role played by some very unassuming creatures: plankton.
In a paper to appear in the online Early Edition of the Proceedings of the National Academy of Sciences (PNAS), Ohio State University researcher Matthew Saltzman and his colleagues show how plankton provided a critical link between the atmosphere and chemical isotopes stored in rocks 500 million years ago.

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Life on Earth dramatically surged around three billion years ago, possibly when primitive forms developed more efficient ways to harness energy from sunlight, according to a study published on Sunday in Nature.
The conclusion is made by scientists at the Massachusetts Institute of Technology (MIT), who built a "genomic fossil", in essence a mathematical model that took 1,000 key genes that exist today and calculated how they evolved from the very distant past.
The collective genome of all life expanded massively between 3.3 and 2.8 billion years ago, and during this time 27 percent of all presently existing gene families came into being, the study suggests.



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Scottish rocks reveal key point in evolution occurred 400 million years earlier

Evidence found in Scottish rocks has revealed that a critical point in evolution took place 1.2 billion years ago - several hundred million years earlier than scientists had previously understood.
The findings - published (Thursday November 11) in Nature - could lead to new understandings of when complex life - from which humans eventually emerged - evolved on Earth.
Until now scientists had believed an important shift in the levels of oxygen in the Earth's atmosphere took place 800 million years ago.
This increase in oxygen marked the beginning of a move from simple organisms - which had inhabited the planet until this time - to the development of complex multi-cellular organisms which eventually led to life on Earth as we know it.
Chemical signatures of bacteria found in ancient rocks near Lochinver in the north-west Highlands of Scotland, has provided evidence that this key event in evolution actually took place some 400 million years earlier.

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The discovery of a new chemical reaction on tiny particulates in the atmosphere could allow scientists to gain a glimpse from ancient rocks of what the atmospheres of the Earth and Mars were like hundreds of millions years ago, scientists said.
A team of chemists at the (University of California) UC San Diego said the findings also provided a simple chemical explanation for the unusual carbonate inclusions found in a meteorite from Mars that was once thought by some scientists to be evidence of ancient Martian life.

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Title: Atmospheric oxygen and the evolution of insect gigantism
Authors: VANDENBROOKS, John M., School of Life Sciences, Arizona State University, PO Box 874601, Tempe, AZ 85287, jvandenb@asu.edu, HARRISON, Jon Fewell, School of Life Sciences, Arizona State University, Mail Code 4501, Tempe, AZ 85287-4501, and KAISER, Alex, Dept. of Basic Science, Midwestern University, 19555 N. 59th Ave, Glendale, AZ 85308

Most models estimate that over the last 500 million years atmospheric oxygen has varied from ~12% to 35%. Most strikingly, the giant insects of the late Paleozoic (i.e. dragonflies) existed when atmospheric oxygen was hyperoxic, supporting a role for oxygen in the evolution of insect body size. However, the fact that not all groups during this time period were giant (i.e. ****roaches) coupled with the paucity of the insect fossil record and the complex interactions between oxygen, organisms and communities makes it difficult to definitively accept or reject the historical oxygen-size link. Nevertheless, we have successfully reared dragonflies, ****roaches and a variety of other insect species under varying oxygen levels and the results of these studies do support a link between oxygen and the evolution of insect size: 1) dragonflies and other insect groups do develop and evolve larger body sizes in hyperoxia, while almost all insects develop smaller body sizes in hypoxia; yet ****roaches show no size difference when reared under hyperoxia, 2) insects developmentally and evolutionarily reduce their investment in the tracheal respiratory system when living in higher oxygen levels; suggesting there are significant costs associated with tracheal system structure and function and 3) larger insects invest more of their body in the tracheal system, potentially leading to greater effects of oxygen on large insects. These results provide several mechanisms by which the tracheal oxygen delivery system may be involved in the small size of modern insects and hyperoxia-enabled Paleozoic gigantism. When we begin to examine the fossil record closely, we see that certain groups have responded more strongly to oxygen variation. While taxa such as Protodonata and Paleodictyoptera have gigantic members, they are outliers to an overall pattern of oxygen-mediated body size change. On the other hand, Blattodea contain no giant representatives and demonstrate little effect on maximum body size, but do show shifts in average size correlated with changes in atmospheric oxygen levels. Here we examine the role of atmospheric oxygen in the evolution of insect body size and discuss the possibility of imaging fossil tracheae as a proxy for paleo-oxygen levels. This research was supported by NSF EAR 0746352 and DOD 3000654843 to JH and JVB.

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Title: Phanerozoic concentrations of atmospheric oxygen reconstructed from sedimentary charcoal
Authors: Ian J. Glasspool & Andrew C. Scott

Variations of the Earth's atmospheric oxygen concentration (pO2) are thought to be closely tied to the evolution of life, with strong feedbacks between uni- and multicellular life and oxygen. On the geologic timescale, pO2 is regulated by the burial of organic carbon and sulphur, as well as by weathering. Reconstructions of atmospheric O2 for the past 400 million years have therefore been based on geochemical models of carbon and sulphur cycling. However, these reconstructions vary widely, particularly for the Mesozoic and early Cenozoic eras. Here we show that the abundance of charcoal in mire settings is controlled by pO2, and use this proxy to reconstruct the concentration of atmospheric oxygen for the past 400 million years. We estimate that pO2 was continuously above 26% during the Carboniferous and Permian periods, and that it declined abruptly around the time of the Permian-Triassic mass extinction. During the Triassic and Jurassic periods, pO2 fluctuated cyclically, with amplitudes up to 10% and a frequency of 20-30 million years. Atmospheric oxygen concentrations have declined steadily from the middle of the Cretaceous period to present-day values of about 21%. We conclude, however, that variation in pO2 was not the main driver of the loss of faunal diversity during the Permo-Triassic and Triassic-Jurassic mass extinction events.

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Fractal haze may have warmed the early Earth

A haze of fluffy fractal-shaped particles may have helped protect early life from harmful ultraviolet radiation, a new study suggests. The aerosols could help resolve a long-standing puzzle about how the early Earth stayed warm.
Billions of years ago, the sun emitted up to 30 per cent less light than it does today. That should have made the early Earth too cold to maintain liquid water on the surface until about 2 billion years ago. But geological studies of banded iron formations and other materials that can form in water suggest liquid water pooled on the surface much earlier.

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Comets from outer space may have created Earth's atmosphere not volcanoes spewing out gases from deep within the planet.
The origin of the gases in Earth's atmosphere has long been a puzzle. One of the main theories is that the gases bubbled up out of the mantle via volcanoes.

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