Geothermal heat comes from within

I enjoyed your article on solar energy and applaud your efforts.

I enjoyed your article on solar energy and applaud your efforts (“Special Report: Photonics and the energy crisis,” September, p. 68). We have solar panels on our home’s roof and enjoy putting power back on the grid.

One minor item in one of the articles caught my eye that I don’t believe is correct (“Catching up with the plant kingdom,” In the first sentence you attribute geothermal power to the Sun. The Sun does an impressive job of warming the Earth’s surface; however, geothermal power is generally associated with volcanic activity whose energy comes from within the Earth. The Earth’s internal heat comes from two main sources: (1) the impact of asteroids and gravitational collapse of material as the Earth bulked up early in our solar system’s history (yes, the Earth and asteroids were orbiting around the protosun/Sun, but I don’t think that is what you meant) and (2) radioactive decay of some isotopes, mainly potassium, uranium, and thorium.
Andrew Calvert
U.S. Geological Survey

Thanks for spelling it out

I have been in the optical business for 30 years and I am still unable to keep up with constantly evolving acronyms. I am comfortable with laser and LED, but would never have known that SERS stood for “surface-enhanced Raman scattering” had your writer not explained it in her October article. It is not uncommon for me to give up on articles in other journals that are incomprehensible because of obscure initials and acronyms.

Your policy of explaining every acronym (even LED) is greatly appreciated.
Rod Livingston
Beta LaserMike Inc.

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