We present new estimates of protosolar elemental abundances based on an improved combination of solar photospheric abundances and CI chondritic abundances .
These new estimates indicate CI chondrites and solar abundances are consistent for 60 elements .
Our estimate of the protosolar “ metallicity ” ( i.e .
mass fraction of metals , Z ) is 1.40 % , which is consistent with a value of Z that has been decreasing steadily over the past three decades from \sim 1.9 \% .
We compare our new protosolar abundances with our recent estimates of bulk Earth composition ( normalized to aluminium ) , thereby quantifying the devolatilization in going from the solar nebula to the formation of the Earth .
The quantification yields a linear trend \log ( f ) = \alpha \log ( T _ { C } ) + \beta , where f is the Earth-to-Sun abundance ratio and T _ { C } is the 50 % condensation temperature of elements .
The best fit coefficients are : \alpha = 3.676 \pm 0.142 and \beta = -11.556 \pm 0.436 .
The quantification of these parameters constrains models of devolatilization processes .
For example , the coefficients \alpha and \beta determine a critical devolatilization temperature for the Earth T _ { \mathrm { D } } ( \mathrm { E } ) = 1391 \pm 15 K. The terrestrial abundances of elements with T _ { C } < T _ { \mathrm { D } } ( \mathrm { E } ) are depleted compared with solar abundances , whereas the terrestrial abundances of elements with T _ { C } > T _ { \mathrm { D } } ( \mathrm { E } ) are indistinguishable from solar abundances .
The abundances of noble gases and hydrogen are depleted more than a prediction based on the extrapolation of the best-fit volatility trend .
The terrestrial abundance of Hg ( T _ { C } = 252 K ) appears anomalously high under the assumption that solar and CI chondrite Hg abundances are identical .
To resolve this anomaly , we propose that CI chondrites have been depleted in Hg relative to the Sun by a factor of 13 \pm 7 .
We use the best-fit volatility trend to derive the fractional distribution of carbon and oxygen between volatile and refractory components ( f _ { \mathrm { vol } } , f _ { \mathrm { ref } } ) .
For carbon we find ( 0.91 \pm 0.08 , 0.09 \pm 0.08 ) ; for oxygen we find ( 0.80 \pm 0.04 , 0.20 \pm 0.04 ) .
Our preliminary estimate gives CI chondrites a critical devolatilization temperature T _ { \mathrm { D } } ( \mathrm { CI } ) = 550 ^ { +20 } _ { -100 } K .