Di sorga apa ada oxygen?

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When life as we know it became possible on Earth

The mystery of how our planet's atmosphere became rich in oxygen has finally 
been solved

By Steve Connor, Science editor

Thursday, 9 April 2009

It was one of the most important changes to have happened to the Earth's 
atmosphere and it was the reason why today we can breathe life-giving oxygen. 
And yet the Great Oxidation Event has remained a mystery – until now.

Without oxygen, life on Earth would not exist as we know it. It has provided 
the supercharged air that has fuelled an explosion in the diversity and size of 
all living organisms, from the smallest shrimp to the biggest dinosaur.

About 21 per cent of air is oxygen, a vital ingredient for living organisms to 
carry out the most efficient method of converting food into energy using 
aerobic respiration. Yet an oxygen-rich atmosphere did not always exist, and 
the explanation for how it came about has eluded generations of scientists.

Now a team of researchers led by Kurt Konhauser of the University of Alberta in 
Edmonton, Canada, has come up with a convincing explanation for why oxygen 
suddenly began to accumulate in the early atmosphere of the Earth about 2.7 
billion years ago, when life consisted of nothing more complex than single-cell 
microbes.

The Great Oxidation Event happened, they believe, when one group of 
oxygen-destroying microbes began to die off, leaving another group of 
oxygen-producing microbes to gain the ascendancy. The trigger for this event 
was a fall in a trace metal called nickel, which led to the inexorable rise of 
oxygen – and life – on Earth.

The role of nickel in the story of atmospheric oxygen is new. If Professor 
Konhauser and his colleagues are right then it could explain not just the 
explosive evolution of life, but how the Earth itself was shaped, because it 
the erosive power of oxygen that was so crucial to the sculpturing of rocks, 
the formation of rivers and the carving out of the coastlines.

"The Great Oxidation Event is what irreversibly changed surface environments on 
Earth and ultimately made advanced life possible. It was a major turning point 
in the evolution of life on our planet, and we are getting closer to 
understanding how it occurred," said Dominic Papineau of the Carnegie 
Institution in Washington.

Oxygen as a molecule is so reactive that it soon disappears unless it is being 
constantly produced. The concentration of oxygen in the atmosphere today is 
maintained by plants carrying out photosynthesis – the conversion of sunlight 
into chemical energy and oxygen.

The first photosynthetic microbes, the "blue-green" algae or cyanobacteria, are 
thought to have evolved about 300 million years before the Great Oxidation 
Event 2.5 billion years ago. But the oxygen they produced was quickly destroyed 
by the methane gas produced by the far more numerous methanogenic bacteria, 
which could breathe without oxygen using the less efficient method of anaerobic 
respiration.

These methanogenic bacteria, which still live in the waterlogged, 
oxygen-starved environment of swamps and wetlands, crucially need nickel to 
survive. Without a rich supply of nickel, the vital enzymes of these 
methane-producing microbes are fatally undermined.

The scientists found that by analysing a type of sedimentary rock known as 
banded-iron formations they could monitor levels of nickel in the oceans of the 
early Earth dating as far back as 3.8 billion years ago. They found there was a 
marked fall in nickel between 2.7 billion and 2.5 billion years ago – the same 
time as the Great Oxidation Event.

"The timing fits very well. The drop in nickel could have set the stage for the 
Great Oxidation Event. And from what we know about living methogens, lower 
levels of nickel would have cut back methane production," Dr Papineau said.

"The nickel connection was not something anyone had considered before. But our 
study indicates that it may have had a huge impact on the Earth's environment 
and on the history of life," he said.

Professor Konhauser said that the study, published in Nature, supports the idea 
that these methane-producing microbes prevented oxygen from accumulating in the 
early atmosphere for hundreds of millions of years.

The scientists believe that nickel levels fell because the Earth's crust had 
cooled down during this period, which meant that there was less nickel being 
ejected from volcanic eruptions into the ocean.

"We're certain from looking at the rocks in banded-iron formations that nickel 
dropped about 2.5 billion years ago to about half its previous value. The issue 
is how the methane-producing microbes responded to this decrease in nickel. We 
think they died off," Professor Konhauser said.

Although the Great Oxidation Event did not lead to a sudden rise of oxygen to 
levels like those experienced today, it did cause a significant rise that has 
never been reversed.


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Jusfiq Hadjar gelar Sutan Maradjo Lelo


Allah yang disembah orang Islam tipikal dan yang digambarkan oleh al-Mushaf itu 
dungu, buas, kejam, keji, ganas, zalim lagi biadab hanyalah Allah fiktif.



      

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