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A fountain of lava erupts from Hawaii's Kilauea Iki crater on Dec. Two rock samples from this eruption contain geochemical anomalies that could date back 4.5 billion years, shortly after the Earth first formed. Some geologists assume that this slow circulation would have wiped away any geochemical traces of Earth's early history long ago.
Eaton Earth's mantle is made of solid rock that nonetheless circulates slowly over millions of years.
In the case of tungsten, which has many isotopes, the important ratio is tungsten-182 to tungsten-184.
The heavier isotope, tungsten-184, is stable and has existed since the planet first formed.
Tungsten tends to associate with metals, so most of it migrated to Earth's core, while hafnium, which tends to associate with silicate minerals, stayed in Earth's mantle and crust.
Alternatively, the rocky outer surface of the Earth might have formed in patches, with vast magma oceans in between.
Parts of these magma oceans may have crystallized and sunk to the boundary between the mantle and the core, preserving the ancient tungsten and helium signatures.
But a new study led by University of Maryland geologists has found new evidence that could date back more than 4.5 billion years.
The authors of the research paper, published April 7 in the journal Science, studied volcanic rocks that recently erupted from volcanoes in Hawaii and Samoa.
"Nearly all of these anomalies formed within the first 50 million years after the solar system formed," Mundl said.