Lecturing 2 3rd grade classes on "Earth's Place in the Solar System", BUT...

[Whirligig Girl]

Oh, Thanks for the reminder, I totally forgot about the ice ages. THis means that even in it's current position, the Earth isn't always... erm... "Locked Golden".

[Wahgineer]

Where do you get this from? Even at its current position, Earth has experienced times when its oceans have almost completely frozen over. I see no reason to expect that Earth would maintain any open surface water if it were located at the distance of Mars. I also would expect Earth's atmosphere/hydrosphere to have evolved differently if it were closer to the Sun where Venus is located. The higher temperatures there would have kept the water vapor in the atmosphere (instead of almost all of it condensing out into the oceans) where photodissociation would have split it into hydrogen (which escapes) and oxygen (which reacts with surface materials). There is certainly a distance from the Sun where the Earth would have been too hot for our liquid water oceans to form, and there is certainly a distance from the Sun where Earth would be completely frozen over. There will be similar boundary distances for planets with other masses or compositions (but those distances may not be exactly the same as for Earth), so the boundaries of the Goldilocks zone are fuzzy because of this. But the concept of the zone is valid.

so we can say that the Goldilocks zone does exist, but it's boundaries are determined by both the star and the planet (but mostly the star).

[Moon Goddess]

Oh, Thanks for the reminder, I totally forgot about the ice ages. THis means that even in it's current position, the Earth isn't always... erm... "Locked Golden".

I think Brotoro isn't refering to Ice Ages, but rather http://en.wikipedia.org/wiki/Snowball_Earth

So reading this it seems your basic complaint is the book says "The Earth sits in a "Goldilocks's Zone" where water can exist in all three states" and you're argument is that can happen at mars and venus orbit so Goldilock's Zone is wrong. But just because it's a wide zone not a narrow zone doesn't mean the book is wrong. Leaving out extra details is not the same as lying.

[cantab]

The habitable zone to my understanding is basically that if a planet is not too close and not too far from its sun, it CAN have liquid water on its surface. That doesn't mean it will. After all, never mind Venus and Mars, the Moon has no oceans and it's in the SAME orbit as the Earth!

The main other factor, of course, being that it needs the right amount and type of air. Not enough, and water can never be liquid. (If you have a vacuum chamber you can demonstrate water boiling at room temperature when the air is sucked out.) Too much carbon dioxide and the surface will be too hot.

[Whirligig Girl]

Looks like you're in the wrong part of NC

Piedmont Triad region.