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Ancient rocks are revealed when Earth Plate Tectonics began

Ancient rocks are revealed when Earth Plate Tectonics began


Tusch and Münker developed a powerful new method for extracting small traces of tungsten from ancient rocks. Then they went looking for the rocks.

They first studied the Archaic Rocks found in the Isua region of western Greenland. Tusch spent 11 months analyzing the samples, but eventually his own tungsten-182 data were flat, with no significant variation between samples. The researchers believed that the rocks of Greenland had deformed and warmed throughout history, confusing geochemical information.

As they needed better rocks, they set out for Pilbar in western Australia. “It has some of the best-preserved rocks in the entire planet,” Münker said. “They haven’t seen much warming compared to rocks of that age.”

“I was very eager to find samples that didn’t show the same value over and over again,” Tush said.

Guided by co-authors Martin Van Kranendonk A team from the University of New South Wales, the group crossed the Outback in outdoor trucks, visiting rust-red outcrops where ancient volcanic rock and vegetation mimic each other: At the exits Spinifex shrubs are part of silica, twisting and not edible at all. but termites. Between 2,700 and 3,500 billion years ago, half a ton of hopeful rocks and lava were formed.

To study the ratios of tungsten isotopes in ancient rocks, geologists extracted and purified their tungsten in exchange for a process called ion chromatography. The dissolved stone sample is charged in an acidic solution, achieving a vertical separation of the different elements.By Jonas Tusch

Returning to Germany, Tusch began work. He used a rock saw inside each sample to get fresh rock, and then smoothed out some slices to make them microscopic up to half the width of a human hair. He crushed the rest and concentrated the tungsten, and then analyzed the isotope ratios of the tungsten on a mass spectrometer.

The results came out in almost two years. This time the isotope ratios were not flat. “It was really nice to see,” Tushch said.

Tungsten-182 concentrations began in rocks formed 3.3 billion years ago, showing that the mantle was not yet mixed. Then, values ​​were reduced by more than 200 billion years, reaching modern levels of 3.1 billion years ago. This decline reflects the dilution of the old tungsten-182 signal when it began to mix in the mantle beneath the Pillar. This mixture shows that plate tectonics began.

The earth would transform quickly the world of water Packed with volcanic islands like Iceland, the world of continents with mountains, rivers and flood plains, lakes and shallow seas.

A new world made for life

Plate tectonics helps to shed light on how it affected life on Earth at a start date of about 3.2 billion years ago.

Life began before, more than 3.9 billion years ago, and in Pilbara he was making small piles in sediments called stromatolites 3.48 billion years ago. This shows that plate tectonics is not an essential condition for life at the basic level. However, this is probably not a coincidence diversified life just as plate tectonics was launched.

With plate tectonics came deep seas of sunlight and lakes fertilized with nutrients derived from the continental rock. In these environments bacteria evolved to collect sunlight through photosynthesis. generating oxygen.

The fossil record shows an explosion of complex and diverse animals about 540 million years ago. One of the most numerous and iconic creatures of the time was the trilobite, an armored animal that flourished for tens of thousands of years. Pictured here is a trilobite fossil Elrathia kingii.By Micha L. Rieser

For another half a billion years, this oxygen barely stopped in the sky, in part because it reacted immediately with iron and other chemicals. Moreover, each oxygen molecule produced in photosynthesis corresponds to a carbon atom, which can be easily recombined into carbon dioxide with no net oxygen gain in the atmosphere unless the carbon is buried.

Gradually, however, plate tectonics provided soils and sediments to bury more and more carbon (at the same time giving a lot of phosphorus to stimulate photosynthetic bacteria). The atmosphere was finally oxygenated 2.4 billion years ago.

Oxygen created the planet, with the appearance of plants, animals and almost everything else with an oxygen-based metabolism. Having a longer and more complex life than microbes requires more energy, and organisms can do much more with the living molecule called ATP and the oxygen they carry with energy without it. “Oxygen is very important for what we consider to be a complex life,” he said Athena Eyster Massachusetts Institute of Technology.



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