MadSci Network: Chemistry

Re: what is the elemental composition of life, universe, and earth?

Date: Sat Aug 9 17:46:23 2003
Posted By: John Christie, Faculty, Dept. of Chemistry,
Area of science: Chemistry
ID: 1056632837.Ch

If you are really interested in this subject, I have a truly excellent book on my shelves:
Chemical Evolution: Origin of the Elements, Molecules, and Living Systems
by Stephen F. Mason
Unfortunately it is now out of print, and may be a little hard to find.

Direct information about the elemental composition of the universe and various parts of it can be found at several websites, and in many books on Geochemistry and Environmental Chemistry.

Here is some of it:
(1) In the solar system, stars in general, and probably the universe as a whole
The most abundant elements are the lighter elements: over 90% hydrogen, several % helium, about 1% everything else. In the "everything else" (a) even numbered elements are more abundant than odd numbered elements (b) abundance tends to fall rapidly with increasing atomic number (c) carbon, oxygen, magnesium, silicon, and iron are anomalously high relative to these general trends, while lithium, beryllium, and boron are anomalously low.

(2) In the Earth's crust
The order of abundance is oxygen (almost 50%), silicon (over 20%), aluminium, iron, magnesium, calcium, sodium, potassium. These are all the sorts of elements that rocks are mostly made out of.

(3) In the Earth as a whole
Because of the core and the mantle, iron, nickel, and magnesium, become more important, but oxygen silicon, aluminium et al remain major overall constituents.

(4) In living things
A large amount of living things is water, or materials closely related to water in elemental composition. But hydrogen is so light that oxygen dominates. Water is 89% oxygen, and only 11% hydrogen by weight. Carbon is the element that is the basis of all life. Other elements that are important and abundant are nitrogen, sulfur, phosphorus, sodium, potassium, calcium, magnesium, and iron (not in that order).

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