I'm getting a little tired of hearing that solar, wind, hydroelectric and geothermal energy are "renewable" sources. Exactly what seeds are we planting to ensure that the wind keeps blowing or the sun keeps shining?

The first three energy sources depend on nuclear fusion, taking place in the sun, where the hydrogen atoms are being converted to helium. Scientists say this will end in about 4 billion more years.

Geothermal energy is a little more mysterious to me. Is it caused by nuclear reactions deep within the earth or simply by gravitational pressure? Either way, I don't think it is any more renewable than the other three.

For all practical purposes, a more appropriate word would be "inexhaustible." Why don't we use that? Oh yeah — that's the word we used to use for our oil and coal resources.

Jonathan D. Whitney