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C00002 00002		Thanks for your reply.  I had an answer to that problem, but
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	Thanks for your reply.  I had an answer to that problem, but
at this late date, I can't assure you that I mentioned it in my lecture,
although I was thinking about interactions.

	The answer involved multiplying the energy used in extracting
minerals today by the ratio of the presently mined ore concentrations
to the concentrations in the earth's crust and use this as an estimate
of the energy required to handle the lower concentration ores.  Since
only a fraction of energy use today is in the extractive industries,
it doesn't amount to a large increase in total energy use.  At the
time I wrote, the total energy use of mankind amounted to $1\over 50,000$
of the solar energy striking the earth.

	Speaking of the biological approach,