Erin Wayman’s article “Faint young sun” (SN: 5/4/13, p. 30), about how the early Earth stayed warm enough for liquid water, made me wonder about the effect of the temperature of the planet itself. A hotter core, thinner crust, more volcanism — wouldn’t those factors in addition to atmospheric influences affect surface temperature?
Virginia Bruce, via e-mail
“For the present-day climate, internal heat provides only 0.02 percent of the energy input to the climate system,” says Georg Feulner of Germany’s Potsdam Institute for Climate Impact Research. Scientists estimate that heat flow 3.8 billion years ago was three times as high as today, still negligible compared with energy from the sun. — Erin Wayman