Coragyps

A couple of items that I thought were sort of neat:
<a href="http://www.discover.com/nov_02/featcircles.html" target="_blank">Here</a> is a maybe somewhat simplistic piece which indicates that maybe our earth could be in a fairly elliptical orbit, and we could still be here after all. Some IDer's and other creationists point to our moderately circular orbit as "proof" that it was made that way by an Intelligence. I've seen it said that, "If we were a million miles closer to the sun, we'd all be dead," despite the fact that we are three million miles closer every January.

I just finished reading Trilobite - Eyewitness to Evolution by Richard Fortey. He has a great illustration of why "purely transitional" species are rare in the geologic record:

Heathen Dawn

Nice excuse.

pz

No, nice explanation. It's a good analogy to explain a complex phenomenon to someone not trained in the topic.

lpetrich

It would be VERY interesting to redo these calculations with different inclinations of spin axis to orbit axis. What would happen if Earth had a Uranus-like orientation? (nearly 90 degrees) Or a Jupiter-like one? (nearly 0)

Also interesting to find out would be typical patterns of rainfall. Will the pattern of wet and dry areas remain similar as the Earth's orbit eccentricity increases?

[ November 24, 2002: Message edited by: lpetrich ]</p>

Coragyps

lp: I would think that the research got into some of the details of climate patterns - they used one of the fairly sexy climate simulators to do the work. I would be neat to see what inclination of the axis did - though some of the YEC crowd must already know. I've also seen the claim that one degree more or less, and we'd all be dead. (The fact that our inclination varies by about that much apparently was lost on them....)
My guess would be that either change would play hell with weather patterns, given that the pretty small Milankovich cycles drive all the variation that they do.

lpetrich

Here is <a href="http://www.solstation.com/habitable.htm" target="_blank">a discussion of various habitable zones</a>. From that discussion, it may seem that the Earth is conveniently placed in the Galaxy and in the Solar system, and that it conveniently has a large moon, which helps stabilize its spin orientation.

However, the Galaxy contains ~10^11 stars, which can easily compensate for the improbability of the Earth's circumstances.

xeren

The thing that i find is that people that say things like "if the earth was too close or far, we would all die" have never heard of the Anthropic principle.

<a href="http://zebu.uoregon.edu/~imamura/209/mar31/anthropic.html" target="_blank">Anthropic Principle</a>

[ November 25, 2002: Message edited by: xeren ]</p>

beausoleil

Seems to me to be a bit of a straw man - the point is surely that the Earth has remained habitable over 4.5 Ga because planetary orbits in our solar system are stable on that timescale and because it has been in the habitable zone. For argument's sake, how long could the Earth maintain a highly elliptical orbit in our solar system (rest 'as is') or a solar system with other planets also on highly elliptical orbits? Wouldn't chaotic evolution of the orbits kick in and a stable climate be impossible?

lpetrich

In fact, in some orbit simulations with crossing orbits, the lighter planets get ejected after while -- they eventually get too close to the heavier ones.

[ November 25, 2002: Message edited by: lpetrich ]</p>