Science News - October 8, 2011

Lowdown on Earth’s heat “Science Stats” (SN: 8/27/11, p. 4) under states the power Earth radiates into space and mistakenly suggests that Earth radiates more energy from inter nal sources than it receives from the sun. The total (44 trillion watts) shown in your diagram must represent only the minuscule percentage (about 0.02 percent) from internal energy sources (radioactivity, tidal, remnant gravita tional energy) that cause surface effects like volcanoes and plate tectonics. In fact, Earth receives about 174,000 tera watts from the sun and radiates the same amount. Strictly speaking, Earth doesn’t radiate any “heat.” Instead, it emits energy in the form of light, pre dominantly at infrared wavelengths because of its modest temperature. Don McCarthy, Tucson, Ariz.

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The reader is correct. The diagram presents heat flow only from Earth’s internal energy sources. — Camille M. Carlisle

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Zapped on units
The article “Dolphin can sense electric
fields” (SN: 8/27/11, p. 12) contains
an error in the sentence, “Paco could
perceive a current as weak as 4.6 micro
volts per centimeter….” Current is
measured in amperes, whereas electric
field is measured in volts per meter.
Robert P. Yassanye, Sarasota, Fla.

The reader is correct. Paco perceived an electric field, as the reported units indicate, not current. — Nadia Drake

Correction
In “Tumor tellall” (SN: 9/24/11,
p. 18), a diagram on Page 21 incorrectly
omitted coloring showing a segment
of chromosome 15 that remained after
another part of the chromosome had
been deleted. See the correct version
online at http://bit.ly/SN Tumor