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TOPIC: Evolution of the atmosphere


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Earth's atmosphere
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Earth's atmosphere 'created by meteorites'

Earth's atmosphere came from outer space, its gases arriving in a meteorite bombardment billions of years ago, scientists claimed yesterday.
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"Some of Earth's largest and most important nickel sulphide ore deposits formed during the Archean and early Proterozoic, between 2,900 and 1,800 million years ago. Establishing the origin of the metals and sulphur in these deposits is critical for understanding how these important deposits formed and their relationship to the evolution of our planet and its environment" - Professor Mark Barley.

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Much of our planet's mineral wealth was deposited billions of years ago when Earth's chemical cycles were different from today's. Using geochemical clues from rocks nearly 3 billion years old, a group of scientists including Andrey Bekker and Douglas Rumble from the Carnegie Institution have made the surprising discovery that the creation of economically important nickel ore deposits was linked to sulphur in the ancient oxygen-poor atmosphere.
These ancient ores - specifically iron-nickel sulphide deposits -  yield 10% of the world's annual nickel production.  They formed for the most part between two and three billion years ago when hot magmas erupted on the ocean floor. Yet scientists have puzzled over the origin of the rich deposits. The ore minerals require sulphur to form, but neither seawater nor the magmas hosting the ores were thought to be rich enough in sulphur for this to happen.

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-- Edited by Blobrana on Sunday 22nd of November 2009 05:48:10 PM

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Great Oxidation Event
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Ancient Ocean Oxygen Production Began 100 Million Years Earlier than Thought
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.
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 at Riverside (UCR) corroborates recent evidence that oxygen production began in Earth's oceans at least 100 million years before the GOE.

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RE: Evolution of the atmosphere
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Banded rocks reveal early Earth conditions, changes
The strikingly banded rocks scattered across the upper Midwest and elsewhere throughout the world are actually ambassadors from the past, offering clues to the environment of the early Earth more than 2 billion years ago.
Called banded iron formations or BIFs, these ancient rocks formed between 3.8 and 1.7 billion years ago at what was then the bottom of the ocean. The stripes represent alternating layers of silica-rich chert and iron-rich minerals like hematite and magnetite.
First mined as a major iron source for modern industrialisation, BIFs are also a rich source of information about the geochemical conditions that existed on Earth when the rocks were made. However, interpreting their clues requires understanding how the bands formed, a topic that has been controversial for decades, says Huifang Xu, a geology professor at the University of Wisconsin-Madison.

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Ancient oceans yield clues to the origins of animal life on Earth
Analysis of a rock type found only in the worlds oldest oceans has shed new light on how large animals first got a foothold on the Earth.
By analysing the isotopes of chromium in iron-rich sediments formed in the ancient oceans, a scientific team, led by Professor Robert Frei at the University of Copenhagen in Denmark, has found that a rise in atmospheric oxygen levels 580 million years ago was closely followed by the evolution of animal life.

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Great Oxidation Event
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How Earth Got its Oxygen
The first half of Earth's history was devoid of oxygen, but it was far from lifeless. There is ongoing debate over who the main biological players were in this pre-oxygen world, but researchers are digging up clues in some of the oldest sedimentary rocks on the planet.
Most scientists believe the amount of atmospheric oxygen was insignificant up until about 2.4 billion years ago when the Great Oxidation Event (GOE) occurred. This seemingly sudden jump in oxygen levels was almost certainly due to cyanobacteria - photosynthesising microbes that exhale oxygen.

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Title: New constraints on the delivery of cometary water and nitrogen to Earth from the 15N/14N isotopic ratio
Authors: D. Hutsemekers, J. Manfroid, E. Jehin, C. Arpigny

New independent constraints on the amount of water delivered to Earth by comets are derived using the 15N/14N isotopic ratio, measured to be roughly twice as high in cometary CN and HCN as in the present Earth. Under reasonable assumptions, we find that no more than a few percent of Earth's water can be attributed to comets, in agreement with the constraints derived from D/H. Our results also suggest that a significant part of Earth's atmospheric nitrogen might come from comets. Since the 15N/14N isotopic ratio is not different in Oort-cloud and Kuiper-belt comets, our estimates apply to the contribution of both types of objects.

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Posts: 130245
Date:
Great Oxidation Event
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The first half of Earth's history was devoid of oxygen, but it was far from lifeless. There is ongoing debate over who the main biological players were in this pre-oxygen world, but researchers are digging up clues in some of the oldest sedimentary rocks on the planet.
Most scientists believe the amount of atmospheric oxygen was insignificant up until about 2.4 billion years ago when the Great Oxidation Event (GOE) occurred. This seemingly sudden jump in oxygen levels was almost certainly due to cyanobacteria - photosynthesising microbes that exhale oxygen.

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Earths atmosphere
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Researchers were stunned to discover recently that Earth is losing more of its atmosphere than Venus and Mars, which have negligible magnetic fields.
This may mean our planet's magnetic shield may not be as solid a protective screen as once believed when it comes to guarding the atmosphere from an assault from the sun.

"We often tell ourselves that we are very fortunate living on this planet because we have this strong magnetic shield that protects us from all sorts of things that the cosmos throws at us - cosmic rays, solar flares and the pesky solar wind" - Christopher Russell, a professor of geophysics and space physics at the University of California, Los Angeles.

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