To me it's the sun. I mean how amazing is it, that the sun is something like 92,000,000 miles from earth & we get heat from it ? It's my understanding that if the earth was just 3% closer or 3% farther away we couldn't survive. Not 5% one way and 1% the other way, or 4% one way and 2% the other way. But 3% in both directions. In other words the earth's distance from the sun is in the exact right spot for life to survive on earth...... Absolutely amazing.