A team of researchers at the Australian National University in Canberra, Australia, has produced the most comprehensive estimate yet of Earth’s composition which will help scientists understand how our planet formed about 4.6 billion years ago. The research is published in the journal Icarus (arXiv.org preprint).
A ‘Blue Marble’ image of the Earth taken from the VIIRS instrument aboard NASA’s Earth-observing satellite Suomi NPP (named in honor of Verner E. Suomi of the University of Wisconsin). This composite image uses a number of swaths of the Earth’s surface taken on January 4, 2012. Image credit: NASA / NOAA / GSFC / Suomi NPP / VIIRS / Norman Kuring.
Our Solar System began as a dense blob in a molecular cloud of hydrogen gas and dust that collapsed under its own gravity, forming the early Sun and planets. The Earth’s chemical composition was set at that early stage of formation.
“The four most abundant elements (O, Mg, Si, and Fe) make up more than 90% of the Earth’s mass, but working out exactly what the planet is made of is tricky,” said co-author Dr. Charley Lineweaver.
“Seismological studies of earthquakes inform us about the Earth’s core, mantle and crust, but it’s hard to convert this information into an elemental composition.”
“Our deepest drilling has only scratched the surface down to 10 km of our 6,400-km radius planet.”
“Rocks at the surface only come from as deep as the upper mantle.”
Dr. Lineweaver and his colleagues, Haiyang Wang and Professor Trevor Ireland, made the most pricise estimate yet of the Earth’s composition based on a meta-analysis of previous estimates of the mantle and core, and a new estimate of the core’s mass.
“From a heterogeneous set of literature values, we present the most complete lists of the elemental abundances with uncertainties of the primitive mantle, the core and the bulk Earth,” they said.
“The four most abundant elements (O, Mg, Si, and Fe) make up 94.19% of the total primitive mantle mass. Fe-Ni alloy accounts for 87.90 wt% of the total mass of the core, and the major light elements in the core are Si, O, S, C, Cr, Mn, P, Co, Na, Mg and H in order of decreasing abundance.”
Compared to previous work, the most significant differences include: our abundances of Mg, Sn, Br, B, Cd and Be are more than 1 sigma lower; and our abundances of Na, K, Cl, Zn, Sr, F, Ga, Rb, Nb, Gd, Ta, He, Ar and Kr, more than 1 sigma higher.”
“This set of concordance estimates (with uncertainties) for the elemental abundances of primitive mantle, core and bulk Earth provides a reference that can be used to compare the Earth to the Sun, which will lead to a more precise devolatilization pattern, potentially applicable to exoplanets and their host stars.”
“Our work focused on getting realistic uncertainties so that our reference model can be used in future comparisons of the Earth with the Sun, or with Mars or with any other body in the Solar System,” Wang said.
“Planetary researchers would find many uses for this new composition record,” Professor Ireland added.
“This will have far-reaching importance, not only for planetary bodies in our Solar System but also other planetary systems in the Universe.”
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Haiyang S. Wang et al. 2018. The elemental abundances (with uncertainties) of the most Earth-like planet. Icarus 299: 460-474; doi: 10.1016/j.icarus.2017.08.024
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