Answers to thought Puzzle:  Core/mantle differentiation.  Suppose that initially the concentration of Fe (iron) in the Earth was about 27%.  The concentration of Mg (magnesium) was about 14%.  From laboratory experiments you measure the partition coefficient for Fe in metal/Fe in silicate to be >>1.  You measure the partition coefficient for Mg in metal/Mg in silicate <<1.  Which four of the following do you expect to be true of Earth?
Mg in mantle = 14%,     Mg in core = 14%        Fe in mantle = 27%        Fe in core = 27%
Mg in mantle <14%        Mg in core < 14%        Fe in mantle < 27%        Fe in core < 27%
Mg in mantle >14%        Mg in core > 14%        Fe in mantle > 27%        Fe in core > 27%
 

The total amount of Fe and Mg do not change.  However, the partition coefficient shows that there will be a much higher concentration of Mg in the mantle than the core (D<1) and higher concentration of Fe in the core than the mantle (D>1).  Since the total amount can't change (we don't create or destroy atoms in this process) the mantle must have Mg>14% and Fe<27% and the core must have Mg<14% and Fe>27%.  This can be shown as below.

There are 100 total (14 Mg, 27 Fe, 59 Everything else)       There are the same totals as before.
14/100 = 14% Mg                                                             But there are 23 Fe in core, 1 Mg
27/100 = 27% Fe                                                               and 29 everything else = 53
59/100 = 59% everything else                                              1/53 = 1.9% Mg, 23/53=43% Fe
                                                                                         In the mantle, there are 4Fe, 13Mg
                                                                                           and 30 everything else = 47.
                                                                                          13/47 = 28%Mg, 4/47 = 8.5% Fe
 

Home Page (est.htm)     Previous Page (est1b.html)