One-third (1/3) of the weight of the earth is iron.

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One-third (1/3) of the weight of the earth is iron.
The earth is often said to be "Planet of Water" according to famous words of Gagarin.
This is way of speaking that made much of water covering up 70% of the earth surface.
When judging by the weight, the earth is "Planet of Iron".
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We cannot live without iron.

 The reason why our blood is red is that the hemoglobin in the erythrocyte　(red blood cell) is red.
The structure of the hemoglobin is mainly made of iron.

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It should be also stated by all means that the last material of the nuclear fusion
targeting in the fixed star is iron as it has the most stable nucleus.