[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.

[palmer]

Not likely. Your 1000 feet has a gradient of about 15 degreees (55 near the top depending on latitude) and 70 at the top. That's a very low gradient for heat flux. Consider midsummer on a sunny day. The earth's surface might reach 120F but 6 feet down it is still 60F or so.

Bottom line is that the earth is a very good insulator in general.