[palmer]

The heat flux from the earth's core, through all that rock, is pretty small. You can prove this by digging a hole.

Done?

Good, what's the temperature at the bottom of the hole? Well, maybe not deep enough. The deepest mine (2.5 miles) has a rock temperature of 151F. That's pretty trifling for 2.5 miles down. Asphalt in summer sun can reach 150F. Therefore the sun wins by 2.5 miles.

[wastoute]

I dunno. The mine I used to work in was about a thousand feet deep. It was about 70 degrees F, IIRC. I hear diamond mines in South Africa are deeper and hotter. So a gradient from absolute zero to the temperature on my deck could be considered to have the portion from absolute zero to 70 F due to the earth’s core and the last 20 to 30 F due to sunlight, the way I see it.