DougI

Argued with a stupid YEC (yup, that's redundant) and he used the easily refuted argument about life only existing in particular circumstances. Although I had to explain to him the Earth travels around the sun in an ellipse (not a circle like he claimed) I wasn't sure how much of a degree difference outside a perfect circle it traveled. He argued that anything outside a five degree difference would be impossible, I just wasn't sure about the actual difference.

Principia

I am not sure what you mean by "degree" -- <a href="http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html" target="_blank">eccentricity</a> perhaps? This <a href="http://www.solstation.com/habitable.htm" target="_blank">website</a> also has some info on the habitable zone for earth-like conditions.
Not sure if this helps.

Albion

I read that the eccentricity varies from 0.00 to 0.06 over time spans of many years. Could someone translate that into English? (I mean, what does an ecestricity of 0.06 look like?)

DutchAtheist

While it may be true that the life currently on this planet would never have developed with more than 5 degrees of eccentricity, this doesn't mean all life. If our planet had an orbit with 20 degrees of eccentricity then the YECs would be arguing how lucky we are to have THAT. The exact values for orbits can be found <a href="http://www.seds.org/billa/tnp/data.html" target="_blank">here</a>

Camaban

the only thing that was improbably was having our PARTICULAR conditions (such as the 5% difference)

if our planet was colder or hotter, we'd most likely still have life (within a certain range), merely extremely different life to what we have today that would look at the conditions we live in and recoil in horror.

beausoleil

Our current scientific understanding is that life requires liquid water. That's why Mars and Europa are the current targets for investigation. I would also add that I think a relatively stable climate is almost necessary for civilisation to evolve. It makes sense to me to suggest that factors leading to rapidly changing climate - perhaps large eccentricity or the absence of a large Moon - would make the chance of our having evolved here less. From an anthropic point of view, low eccentricity and a large Moon might be expected observations for us.

Coragyps

Earth's current orbital eccentricity is 0.017, which translates into a slightly squashed circle, 147,000,000 kilometers earth-to-sun the short way and 152,000,000 km the long way. IOW, we're 5 million km (3 million miles) closer to the Sun in January than in July, and receive 7% more energy from the sun in January. Looking at a diagram of our orbit, you would be real hard-pressed to see any difference from a true circle.

I had a discussion a while back with a fundamentalist of some stripe who had been told, and believed, that Earth has the most perfectly circular orbit of all the planets. That isn't true: Venus and Neptune have much lower eccentricities. I wonder who puts out such information, when direct, incontrivertible data from any encyclopedia proves it false?

DougI

Thanks, that's the sort of information I was looking for. The creationist wasn't terribly clear but keep in mind he thinks we only use 10% of our brain, information is physical in form (because he said if we used 100% of our brain we wouldn't need to learn because our brain would be full), PET scanning machines don't exist, etc.

Sunfair

Just out of curiosity, is it specifically carbon-based life? I know we haven't encountered any other kind- but I was wondering if it's generally believed that other kinds of life would also be dependant on water? Like, silicon-based (no Hollywood jokes please), or nitrogen-breathers or whatever- not that I would know, but I like to speculate.

I hope that made sense, I'm kinda tired.

Wyz_sub10

I remember watching a documentary dealing with that issue. It mentioned the possiblity of silicon-based life thriving in a sulphur-rich environment.

I suppose we're are going by what we now right now when we look for life. (i.e. water)