X-Message-Number: 5024
Date: 20 Oct 95 20:10:43 EDT
From: "Steven B. Harris" <>
Subject: CRYONICS: Postscript: Elements of Life

P.S.  Though it does not change the conclusions, I have a small
and pedantic quibble with John Clark when he says:

   >>Nature only uses 92 different types of blocks (the atoms of
the elements), less than 20  are important in making most objects
that interest us, less than 10 for life.<<

   Actually, there are only 81 non-radioactive elements, and if
you count radioactive ones as building blocks, how many you have,
depends on where you are.  On Earth's surface, a total of 91
naturally occurring elements have been identified so far.  As far
as what makes up "objects that interest us," that changes
drastically from decade to decade.  Consider the cases of
germanium for semiconductors, titanium for aerospace, and
(recently) europium for fiberoptics.  Concentration processes
also play tricks on us as to what things are really scarce.  An
article in my C.R.C. notes that rubidium, the 16th most common
element on the Earth's crust, is actually more common than
chlorine.  But few people have heard of rubidium.

   Doubtless because life began in the oceans, the list of
elements necessary for living organisms is quite skewed from
their abundances on land (halogens being particularly off).  On
the other hand, aluminum, which vies only with oxygen and silicon
in the mass which makes up the solid Earth, is not even known to
be essential for life yet.  The number of elements necessary to
life is far longer than the ten Clark supposes, and here is a
list known to be essential to rodents (and presumably humans):

1) Hydrogen
2) Oxygen
3) Carbon
4) Nitrogen
5) Calcium
6) Phosphorus
7) Magnesium
8) Sodium
9) Potassium
10) Chlorine
11) Fluorine
12) Sulfur
13) Iron
14) Cobalt
15) Copper
16) Zinc
17) Manganese
18) Chromium
19) Selenium
20) Iodine
21) Molybdenum
22) Silicon
23) Nickel
24) Tin
25) Arsenic

If we look at "life" overall, we find that vanadium is 
additionally necessary for things like tunicates, and perhaps
land animals as well.  Boron is necessary for plants, and perhaps
also animals.  Nor are we probably completely done with discovery
in this field.  A few elements, like lithium, aluminum, and
bromine, may be conditionally necessary, or necessary is such
small quantities that we have yet to prove it.


                                  S. H.


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