How would life be without thermal energy?

How much more or less energy would the Sun's energy have to be altered by to make life on Earth impossible (or just human life)?

• Assuming everything else remained the same.  I remember hearing when I was very young that just a few thousand miles farther away or closer to the sun, and the Earth would be lifeless.  Then we hear about life on Mars, and I assume I was mislead so many years ago.

• Answer:

  Estimates vary widely.  It's generally assumed that liquid water is necessary to life, so it can be neither too close in nor too far out.  However, planetary atmospheres can radically alter the temperature, either trapping warmth on a far-out planet, or reflecting it from one that's too close in. It's even possible to get energy from sources other than the sun.  There may be life on moons of Jupiter such as Europa, where the ice is warmed by tidal friction and magnetic fields from the planet. Even in the absence of an atmosphere, it may be possible to use the planet itself as shade. It was once theorized that Mercury was tidally locked to the sun in a 1:1 ratio, with one side always burning up, and the other side freezing cold. It was possible, though not likely, that there was a habitable band between the two. So it's hard to say what would have happened if you moved the Earth; it depends too much on your assumptions.  Suffice it to say it's way, way more than 1,000 miles, since the earth's distance to the sun varies by millions of miles over the course of a year. Wikipedia lists papers with estimates from 3/4 of its current distance (about as far as Venus) to 3 times its current distance (beyond Mars).  Other papers give much narrow ranges, some as little as 1 million extra miles out, resulting in a frozen earth that would be inhospitable to life.  Moving the earth permanently a few million miles would be a much bigger change than the variation in the yearly course, but given that the climate changes over time I think those estimates are too closely focused on life-as-we-know-it and earth-as-we-know-it.  Change its location and everything would change. Certainly, it would not be good for human life.  Even on this planet there are patches uninhabitable by humans due to the temperature, and they're just a few thousand miles away.