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Research News: Meteorite bombardment likely to have created the Earth's oldest rocks

Scientists have found that 4.02-billion-year-old silica-rich felsic rocks from the Acasta River, Canada -- the oldest rock formation known on Earth -- probably formed at high temperatures and at a surprisingly shallow depth of the planet's nascent crust. The high temperatures needed to melt the shallow crust were likely caused by a meteorite bombardment around half a billion years after the planet formed. This melted the iron-rich crust and formed the granites we see today. These results are presented for the first time at the Goldschmidt conference in Boston (14 August), following publication in the peer-reviewed journal Nature Geoscience.

The felsic rocks (rocks rich in silica/quartz) found at the Acasta River in Canada, are the Earth's oldest rocks, although there are older mineral crystals*. Scientists have long known that the Acasta rocks are different to the majority of felsic rocks we see today, such as the granites widely used as a building or decorative material. Now a group of scientists from Australia and China have modelled the formation of the oldest Acasta felsic rocks and found that they could only have been formed at low pressures and very high temperatures.

Posted: 2018-09-12
 

Research News: Global warming: Worrying lessons from the past

Fifty-six million years ago, Earth experienced an exceptional episode of global warming. In a very short time on a geological scale, within 10,000 to 20,000 years, the average temperature increased by 5 to 8 degrees, only returning to its original level a few hundred thousand years later. Based on the analysis of sediments from the southern slope of the Pyrenees, researchers from the University of Geneva (UNIGE) measured the impact of this warming on river floods and the surrounding landscapes: the amplitude of floods increased by a factor of eight -- and sometimes even by a factor of 14 -- and vegetated landscapes may have been replaced by arid pebbly plains. Their disturbing conclusions, to be discovered in Scientific Reports, show that the consequences of such global warming may have been much greater than predicted by current climate models.
Posted: 2018-09-12
 

Research News: Ancient farmers spared us from glaciers but profoundly changed Earth's climate

Millennia ago, ancient farmers cleared land to plant wheat and maize, potatoes and squash. They flooded fields to grow rice. They began to raise livestock. And unknowingly, they may have been fundamentally altering the climate of Earth.

A study published in the journal Scientific Reports provides new evidence that ancient farming practices led to a rise in the atmospheric emission of the heat-trapping gases carbon dioxide and methane -- a rise that has continued since, unlike the trend at any other time in Earth's geologic history.

Posted: 2018-09-12
 
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