Washington: A new research has determined that meteorites raining down on Earth 1.5 billion years ago created a debris rich in platinum, which ‘stirred’ down into the interior of the Earth.
A research programme aimed at using platinum as an exploration guide for nickel put up the time scale on the planet’s large-scale convection processes.
According to Report author CSIRO Minerals Down Under Flagship researcher Dr Stephen Barnes, the study group collected a large body of data on the platinum content of lava flows called komatiites, which host some of the world’s major nickel deposits.
“We found that the oldest komatiites have the lowest platinum content,” Dr Barnes said. “The platinum content gradually increases from about 3.5 billion years to 2.9 billion years ago,” he added.
“This tells us that the deep source where the komatiite came from, down near the boundary between the Earth’s core and mantle, was gradually gaining platinum over time,” he said.
The research paper’s authors now think they know why.
“When the Earth’s core formed, it took all the available platinum with it, leaving the mantle and crust with none,” Dr Barnes said.
“It is a nice example of an unexpected fundamental discovery arising from a practical applied science study,” he added.
“Following that, a steady rain of meteorites created the so-called Late Veneer – a thin surface layer of meteorite debris rich in platinum,” he further added.
With time through large-scale convection processes, which now cause plate tectonics, this material was stirred down into the interior of the Earth.
Scientists are now seeing the signal of that stirring, which took about 1.5 billion years to occur.
This is the first time a time scale has been put on the stirring, which has important implications for the people who study the dynamics of mantle processes and the mechanisms that cause plate tectonics, earthquakes and volcanoes.
Combined with some other work by the researchers on sister elements to platinum, iridium and osmium, scientists also now have a new framework for understanding the variations in isotopic ratios of osmium with time.