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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.
New work from a team including Carnegie's Hanika Rizo and Richard Carlson, as well as Richard Walker from the University of Maryland, has found material in rock formations that dates back to shortly after Earth formed.
It is published by Earth formed from the accretion of matter surrounding the young Sun.
However, the concentrations of Hf and W in rocky material can be affected by melting and crystallization, so we also need to know how each element concentrates in common minerals in the mantles of the Moon and Mars. The decay of a short-lived isotope gives us a way of precisely dating events that happened long ago.
The behavior of Hf has been studied experimentally, but this is not true of W. (2003) Behavior of tungsten and hafnium in silicates: A crystal chemical basis for understanding the early evolution of the terrestrial planets. Cosmochemists can determine age differences of only a million years in rocks billions of years old.
The heat of its formation caused extensive melting of the planet, leading Earth to separate into two layers when the denser iron metal sank inward toward the center, creating the core and leaving the silicate-rich mantle floating above.
Over the subsequent 4.5 billion years of Earth's evolution, convection in Earth's interior, like water boiling on a stove, caused deep portions of the mantle to rise upwards, melt, and then separate once again by density.
Because tungsten dissolves enthusiastically in metallic iron and hafnium does not, it is possible to use the abundance of W-182 in rocks formed by melting of the silicate mantle as an indicator of the timing of core formation. While this might seem like a long time, it happened 4.5 billion years ago.
W and emitting two electrons with a half-life of 8.9 million years) of the lunar mantle will enable better constraints on the timescale and processes involved in the currently accepted giant-impact theory for the formation and evolution of the Moon, and for testing the late-accretion hypothesis. Two papers published in this issue of Nature present precise measurements of tungsten isotope composition in lunar rocks that are best explained by the Earth and Moon having had similar composition immediately following formation of the Moon, and then having diverged as a result of disproportional late accretion of material to the two bodies. found small W excess of about 21 parts per million relative to the present-day Earth's mantle in metals extracted from two KREEP-rich Apollo 16 impact-melt rocks, while Thomas Kruijer et al.
Uniform, terrestrial-mantle-like W isotopic compositions have been reported Hf was no longer extant—that is, more than about 60 million years after the Solar System formed. conducted the measurements of the highly siderophile elements and Os isotopes, and was involved in both the interpretations and the writing of the manuscript.
Here we present W isotope data for three lunar samples that are more precise by a factor of ≥4 than those previously reported W excess of 20.6 ± 5.1 parts per million (±2 standard deviations), relative to the modern terrestrial mantle.
The offset between the mantles of the Moon and the modern Earth is best explained by assuming that the W isotopic compositions of the two bodies were identical immediately following formation of the Moon, and that they then diverged as a result of disproportional late accretion to the Earth and Moon. conducted the W isotopic measurements and was involved in both the interpretations and the writing of the manuscript.