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Factoid
2004-May-12, 04:58 PM
Hello Folks,

I hear all this talk about how exceptionally rare Earth is.
Often these people say that if Earth would be one degree off its orbit
or just a little bit closer to the Sun then there wouldn’t be any life on Earth
or any intelligent life. Is any of this true? Just how precise Earth’s orbit should be to sustain life?

Thanks!

Russ
2004-May-12, 06:01 PM
Hello Folks,

I hear all this talk about how exceptionally rare Earth is.
Often these people say that if Earth would be one degree off its orbit
or just a little bit closer to the Sun then there wouldn’t be any life on Earth
or any intelligent life. Is any of this true? Just how precise Earth’s orbit should be to sustain life?

Thanks!

I'm not fully qualified to post an answer but I'll chime in with my opinion.

I think that there are basically two types of people who believe that.

1) People trying to be good scientists
a) A proper scientist takes the position that if it can't be detected, measured, quantified and described mathematically it doesn't exist. Since we cannot yet detect, etc. other Earth like planets, in these peoples view they must be rare or nonexistent.

2) People who need to be important and/or exceptional.
a) Religious persons: Their doctrine teaches them that God created the universe for them to live in. That God made them in his own image and that they are special to him and watches/judges their activities moment by moment. Having other Earth like planets, which God would have had to make and populate, would remove these people from their position of importance. Which is not acceptable to them.
b) Insecure persons: These people, who may or may not believe in God, are in cronic fear. They have a deep seated need to be protected from their fear (which they may or may not be able to name). These fears could be almost anything; taller people, or just people in general, other nations, planet X from beyond the Solar system, heavy traffic, light traffic, big cities, small towns, dogs, cats, etc. ad, infinitum. Pick anything you can think of and there is some one who fears it for some unfathomable reason. But as long as the Earth is the center of the universe and, therefore, important, they feel comforted by this because it makes them important by association.

My response is in no way scientific. Just what I've noticed about people while traveling through my life. I could be completely wrong.

Kaptain K
2004-May-12, 06:15 PM
Many of those who propose that the earth has to be exactly where it is for life to exist are pushing the idea of Intelligent Design. The truth is that the Sun has increased in brightness by about 10% since life evolved on Earth and life is still here. The habitable zone of the Sun is considerably wider than the +/- 1% that these folks toss around.

Master258
2004-May-12, 06:37 PM
Yeah, I queston the whole if we were a inch away we die stuff too.

Factoid
2004-May-12, 06:43 PM
From the orbital mechanics point of view…are there any models that would show how a different Earth orbit would affect the life on earth and or processes that support life on Earth?

ngc3314
2004-May-12, 06:44 PM
Many of those who propose that the earth has to be exactly where it is for life to exist are pushing the idea of Intelligent Design. The truth is that the Sun has increased in brightness by about 10% since life evolved on Earth and life is still here. The habitable zone of the Sun is considerably wider than the +/- 1% that these folks toss around.

In fact, it has been a bit of a puzzle how the surface conditions have stayed as constant as the fossil record implies (the Faint Early Sun issue, which may have been first fully articulated by Carl Sagan). The sun has brightened by something like 30% since its birth (less since photosynthesizing life arose, of course), and it's not obvious how the greenhouse effect would have been modulated to keep the surface temperature in a range, for example, allowing mostly ice-free oceans for almost all that time. It's clear that there are boundaries on such parameters as our orbital radius, eccentricity, atmospheric composition, and age vis-a-vis the Sun'smain-sequence lifetime. The hard part is knowing what they are and what the distributions of these might be for roughly Earth-mass worlds. The same kind of problem pops up in anthropic arguments about Multiverses - we have no faintest clue what the possible ranges of, say, values of c,h,G might be in various inflating bubbles, and thus no clue how "unlikely" a lifebearing Universe might be.

There's a third category of people who wonder about this - a view which starts with a large number of properties which have to be in narrow or (we suspect) unusual ranges to have an Earth which supports a pole-to-pole ecosystem of macroscopic life. Not just liquid water, but a combination of atmospheric makeup and density which may trace back to the moon-producing Big Splat, the possible role of the Moon in keeping our climate from undergoing wild swings (such as we think Mars is subject to). Add to that the anthropically necessary conditions such as not having had Jupiter come migrating through our neighborhood before the solar nebula was swept away, and the whole history of life on Earth which in a non-mystical view of Darwinism didn't actually want to produce intelligent life forms, it just did. If I had to put money down, I'd guess as of today that microbial life is pretty common but Earthlike worlds, teeming with large complex life forms, may indeed be rare.

lek
2004-May-12, 07:04 PM
From the orbital mechanics point of view…are there any models that would show how a different Earth orbit would affect the life on earth and or processes that support life on Earth?

Dont know if/why such models exist
Relevance, (and accuracy) of such model would be a bit questionable imo. Whats the point in knowing what has to be the orbit of planet with earths parameters orbiting this particular star? (Except for estimates for how much time we got before the sky falls on our heads)

Earth may or may not be rare, but that applies to every planet.

ToSeek
2004-May-12, 07:11 PM
As I recall, the basic arguments in Rare Earth (http://www.amazon.com/exec/obidos/tg/detail/-/0387987010/102-0075173-0468148?v=glance) include:

- Our large moon stabilizing our rotation.
- Jupiter deflecting asteroids.
- The early collision that created the moon pulling away a big chunk of crust, making plate tectonics possible. (Plate tectonics facilitates evolution.)
- The effect of asteroid impacts on returning life back to square one (bacteria and such).

Sticks
2004-May-12, 07:15 PM
What about the "Anthropic Cosmological Principal" from Dr Frank Tippler (and another associate) Both were / are athiests, yet there conclusions seemd that the universe is in harmony with personkind. (Have to be PC there)

The Weak Anthropic Principal has quite a load of "just so" and include things like charge on the electron and other fundamental constants.

Sam5
2004-May-12, 07:16 PM
Hello Folks,

I hear all this talk about how exceptionally rare Earth is.


“Why do some suggest that Earth is exceptionally rare?”

I think the answer is fairly simple, because we haven’t found another earth-like planet yet.

Some religious people don’t want us to find one, while some atheists are desperately trying to find one, as if not finding one or finding one will somehow prove the existence or non-existence of “God”.

I think it’s a rather silly debate.

daver
2004-May-12, 07:22 PM
Hello Folks,

I hear all this talk about how exceptionally rare Earth is.
Often these people say that if Earth would be one degree off its orbit
or just a little bit closer to the Sun then there wouldn?t be any life on Earth
or any intelligent life. Is any of this true? Just how precise Earth?s orbit should be to sustain life?

Thanks!

The current habitable zone for an earth-like planet is roughly from Venus to Mars (maybe .8 AU to 1.6 AU). In the past it was smaller (by the by, this is going exactly counter to all those old SF stories where the old civilizations move inwards).

There are other factors that have more credibility. The earth would be a dramatically different planet without the moon; probably not different enough that life wouldn't have evolved, but possibly different enough that complex life wouldn't have evolved. There's a good chance that a technical civilization would be much more difficult if somehow the Mars-sized rock that collided with earth had run into Venus or Jupiter (or Mars) instead.

Most of the planets in the solar system have nearly circular orbits; we don't know how rare this is, but an earth-like planet in a system with a large planet with a highly elliptical orbit isn't too likely.

Jupiter has been suggested as cutting down dramatically the number of impact events on earth.

There's a book, Rare Earth, that goes into this in quite a bit more detail.

It may be that there are loads--billions--of life-bearing planets in the galaxy, but that planets with complex life may be extremely rare--perhaps a dozen, perhaps less. Right now there's just no way of knowing. We do know that life exists on Earth, we know that it wouldn't if Earth were too much closer to the sun (but estimates of how close too close is vary); we know that the Earth could currently be farther from the sun and still support complex life, but we don't know how far. If Earth were significantly farther from the Sun than it is now, it would have gone into a snowball Earth (in this case, entirely frozen); it's not clear how far from the Sun it would have to have formed in order for liquid water to have existed long enough for complex life to have evolved by now.

Anyway, it would be hard to refute these people--there's a grain of truth in their argument. The habitable belt is a lot bigger than they say it is, but the habitable belt grows through time. Right now the Earth is towards the inner edge of the habitable belt, in the past it may have been close to the outer edge. Being past the outer edge in the past isn't a killer--eventually the belt will move and the earth will thaw and life will develop--but it delays things a bit.

Sam5
2004-May-12, 07:36 PM
The current habitable zone for an earth-like planet is roughly from Venus to Mars (maybe .8 AU to 1.6 AU).

Isn’t the “habitable zone” in a solar system something like the “habitable belt” on the surface of the earth? In other words, primitive people with a primitive lifestyle must live somewhere within the warm or cool zones, but they can’t live at the very cold poles. But certain kinds of animals can live near the poles.

If we expect to find human-like creatures on some other planet, then it would seem that that planet should be much like the earth. However, I think we should be able to find non-human-like creatures on some planets that are not so earth-like.

I suppose we could find some kinds of creatures on hotter or colder planets, that might have two legs, two arms, a head, and that walk erect, but they might not be so “human like”.

Swift
2004-May-12, 07:46 PM
I think the habitable zone is bascially defined as average surface temperature between 0C and 100C, in other words, liquid water. No matter how many arms and legs it has, the predominant theory is that life that is biochemically similar to what we are familiar with would require liquid water.

TravisM
2004-May-12, 08:06 PM
I think that our view of what constitutes life is too narrow. There could be plasma clouds on gas giants that are genuine neural networks. There could also be silicon or germanium bassed life existing on some rocky world 10 times the mass of Earth, orbiting a sun 100 times as bright at a distance of 40 AU!
Xerox molecules (like DNA, i.e.: self-replicating) that carry information in descrete units could be constructed from God knows what, pardon the pun. Exotic combinations of elementary particles given enough time could produce 'life.' Given enough time anything is possible, at least in this corner of the universe. ;)
Those dynamics are what make this question so tough to crack in anything approaching my lifetime, and I'm young-ish!

lek
2004-May-12, 08:13 PM
I think that our view of what constitutes life is too narrow. There could be plasma clouds on gas giants that are genuine neural networks.
*clip*

/me fires up radiobeam towards jupiter with message "What are those glowy bits?!"
:D

Sorry i had to do it, and in a futile attempt to appear to be on topic: Yes i agree.

Swift
2004-May-12, 08:43 PM
I understand the argument about the narrow definition of life (dang carbon-based lifeforms), but its the only life we can prove exists. The ideas about other forms have been endlessly debated, both in these forums and elsewhere. I think we need to keep our minds open to "non-traditional" life, but we might not even recognize it when we see it. Heck, there are still arguments about whether viruses on Earth are "alive".

On the flip side, I have no belief that Star Trek got it right and the life even within our galaxy is all humanoid, can drink each other's booze, and can breed with each other. Even if we narrow our search to carbon-hydrogen-oxgyen-nitrogen chemistry in liquid water, that still leaves a lot of possibilites.

daver
2004-May-12, 08:50 PM
I think that our view of what constitutes life is too narrow.
Quite possibly. Right now we have only one example. Soon there may be cybernetic life forms (i'd call a factory that could produce all the mining and processing equipment required to produce another similar factory cybernetic life). It will likely be a long time before we encounter any other types.

There could be plasma clouds on gas giants that are genuine neural networks.
It's hard to see how they could be stable.

There could also be silicon or germanium bassed life existing on some rocky world 10 times the mass of Earth, orbiting a sun 100 times as bright at a distance of 40 AU!

Silicon- or germanium-based life--at least chemical life--seems extremely unlikely. Based on what we know of chemistry and of course influenced by our carbon chauvanism, carbon seems far and away the most likely backbone for life.


Xerox molecules (like DNA, i.e.: self-replicating) that carry information in descrete units could be constructed from God knows what, pardon the pun.

Again, right now carbon and water seem overwhelmingly likely to be part of that mix


Exotic combinations of elementary particles given enough time could produce 'life.'

It's hard to see how you could get quasi-stable groupings in such a situation.


Given enough time anything is possible, at least in this corner of the universe. ;)

I'll concede that there are more things possible than are dreamt of in my philosophy, but I won't grant that anything is possible.

Taibak
2004-May-13, 05:24 AM
Well, as far as I'm concerned the Moon is the best evidence for intelligent life being rare. A collision of the type that produced it would have almost certainly eliminated all life on the planet. If those collisions are fairly common, it will be almost impossible for complex life to evolve before being wiped out with the next impact. On the other hand, the Earth is the only terrestrial planet where this has happened, which suggests that it's a rare event (And I realise we're dealing with a small sample here, but for the time being it's all we have to go on). If that's the case, then there may be a lot of Earth-like planets out there without a convenient meteor shield in orbit. It may also mean that those planets have more extreme climate changes than Earth (no Moon to stablize the planet's axial tilt), although evolution could very well compensate for this one.

Dgennero
2004-May-13, 03:52 PM
What would happen if we had certain different conditions on Earth is nicely described in the book "What if the moon did not exist" http://catalog.waukeganpl.org:90/kids/0,10,938/search/dsolar+system/dsolar+system/1,13,81,B/frameset&FF=dsolar+system+miscellanea&1,1,
Under different conditions life also would be somewhat different.
I have nothing against the concept of a "rare earth", and it seems that intelligent life comparable to ours is not extremely common (no radio contact so far :-? )
But this is no argument for a conscious, creative force imo - we observe what we observe, on what an "ideal" planet we are, because we are what we are, so this improbability-observation is made after the fact.
It just means that life as we know it might be comparatively rare.
We can estimate the probability of intelligent life on other planets by multiplicating the probability factors for certain occurrences, being at least those:
- single star, aged several billion years
- spectrum mid-F to mid-K
- rocky planet of a minimum size that can cling to an atmosphere
- planet within habitable zone
Since we recently found out that at least gas giants are relatively common, so other solar systems are, too, we can expect a solar system in, say, more than 50% of the cases with a single star of said spectrum.
Harder to calculate are the other factors - the probability that life arises, and e.g. the duration of technological civilizations to communicate with.
It might well be that we are alone in our galaxy, but imo improbable that we are, as intelligent life, alone in the universe.

PhantomWolf
2004-May-13, 11:41 PM
I'm a little surprised that no-one hs mentioned that there is another unquie (well to our solar system) feature of Earth that helps it support life. Our Magnetic Field is larger than our atmosphere.

ToSeek
2004-May-14, 03:18 PM
Relevant article (http://www.allsci.com/mars.html) - compares Mars' suitability for life with Earth's.

Kaptain K
2004-May-14, 08:47 PM
From the article:

Four billion years ago, Mars, however, was in the habitable zone. Then, our sun was thirty percent fainter. However, because our sun is slowly getting brighter (which means the Earth is slowly leaving the habitable zone) Mars drifted out of it.
HUH! Mars is not now in the habitable zone, because it is too far away from the Sun, but it was in the habitable zone when the Sun was fainter? Sheeh! :roll:

Bad science:

...Electrons, protons, helium nuclei, all of which are created from the explosion of stars, the sun, and cosmic rays from distant supernova, and all traveling at the speed of light...
Emphasis added.

Cause or effect?

Another importance of plate tectonics is the magnetic field. This is created when the core of humble Earth, which is mostly iron, and when the outermost region of the core, which is a liquid, spin to create a convective movement that produces a magnetic field which surrounds the entire planet... without plate tectonics, this life saving magnetic field wouldn’t be possible
Seems to imply that plate tectonics causes convection. Convection in the core and mantle causes plate tectonics, not the other way around


...on Mars there are mountains and large volcanoes, some of which are the largest in the solar system. This suggests that Mars had plate tectonics but only for a short period of time.
The large shield volcanoes on Mars are evidence that Mars never had plate tectonics. Plate tectonics produces chains of volcanoes (like Hawaii), because the plates move relative to hot spots in the the lower levels. Olympus Mons is so large, because the plate just sat over the hot spot for millions of years.

There's more, but that is enough for now.

George
2004-May-14, 10:09 PM
"Why do some suggest that Earth is exceptionally rare?"

Because only the surface is cooked, so most of it is red on the inside and even quivers a little. :wink:

Ok, ok...it is Friday at 5, though.

Seriously, the simple lack of data on other star systems is a real problem. "Input, must have input" - 5 Alive, right?

Taibak
2004-May-15, 04:48 AM
I'm a little surprised that no-one hs mentioned that there is another unquie (well to our solar system) feature of Earth that helps it support life. Our Magnetic Field is larger than our atmosphere.

True. And isn't that another result of something smacking into the Earth? As I understand it, whatever hit us not only formed the Moon, but left its core on Earth.

Brady Yoon
2004-May-15, 04:53 AM
Not really. The Earth already differentiated when the protoplanet hit Earth. It was mostly the mantle that was torn apart.

Taibak
2004-May-15, 04:57 AM
Not really. The Earth already differentiated when the protoplanet hit Earth. It was mostly the mantle that was torn apart.

True, but that doesn't mean that it didn't need to re-differentiate after being struck. That is, the protoplanet's core would have sunk through the mantle and mixed with the Earth's core, creating a much bigger core.

Ilya
2004-May-18, 03:55 AM
I think the habitable zone is bascially defined as average surface temperature between 0C and 100C, in other words, liquid water. No matter how many arms and legs it has, the predominant theory is that life that is biochemically similar to what we are familiar with would require liquid water.

100C is a rather parochial number, for it is dependent on the surface pressure. On planets with higher atmospheric pressure water boils at higher temperature, hence liquid-water range is greater. (Freezing point is almost unaffected by pressure.)

Jpax2003
2004-May-18, 04:50 AM
I think the habitable zone is bascially defined as average surface temperature between 0C and 100C, in other words, liquid water. No matter how many arms and legs it has, the predominant theory is that life that is biochemically similar to what we are familiar with would require liquid water.

100C is a rather parochial number, for it is dependent on the surface pressure. On planets with higher atmospheric pressure water boils at higher temperature, hence liquid-water range is greater. (Freezing point is almost unaffected by pressure.)Well, if water expands when it freezes would higher pressures prevent that and create supercooled water instead, thus changing the freezing temp?

Rain Dog
2004-May-18, 07:47 AM
Well, if water expands when it freezes would higher pressures prevent that and create supercooled water instead, thus changing the freezing temp?

Here is a link (http://www.lsbu.ac.uk/water/phase.html)to a phase diagram of water with some explanation. As you can see, the melting point of water is essentially unchanged at pressures up to 100 atmospheres (1 atm is about 10^5 Pa), but the boiling point at that pressure is around 300C. So I agree with Ilya that the habitable zone has more potential for pushing inward than outward, if we think liquid water is a requirement. My own opinion is that ubiquitous liquid SOMETHING is a necessity, but not necessarily water, so I’m very curious to see what we find on Titan.

-RD

edit: atm to Pa conversion wrong :oops:

oynaz
2004-May-18, 09:31 AM
Is the "something huge crashed into us and created the moon"-theory accepted as the truth? I thought it was only one of many theories.

ToSeek
2004-May-18, 02:14 PM
Is the "something huge crashed into us and created the moon"-theory accepted as the truth? I thought it was only one of many theories.

All scientific theories are tentative to some extent, but the Mars-sized body collision seems to be the one with the best explanatory power. No one can come up with a scenario using any of the other hypotheses that results in the composition and nature of the Earth-Moon system matching what we see.

beskeptical
2004-May-18, 04:39 PM
I think the Lunar rocks have added a lot of weight to the big impact hypothesis of the Moon's origin.

Another intriguing mystery of life's survival range is the fact that earthquakes and undersea eruptions release massive amounts of microbial life from beneath the sea floor. And, the evidence for life deep within the Earth's crust has been increasing.

Life does not need Sun light.
The temperature range has been found to be much higher than previously thought. Try a google search on thermophiles.
Life exists in many extremely toxic environments. Check out extremophiles.

And, we have no way of knowing if we have discovered all the possibilities yet. We only know our previous conception of life's limits were wrong.

Master258
2004-May-18, 04:47 PM
I remeber something in Astronomy about this a few years back. Let me see If i can find it.

eburacum45
2004-May-18, 06:02 PM
Extremophiles and thermophiles could survive on a planet which was not Earth-like; they may be common in the galaxy, depending on how life arises in the first place (not yet known).

But we are discussing Earth-like worlds;
it has always seemed very unlikely to me that there will be many worlds in our galaxy where an unprotected human could step out of a spaceship and be able to tolerate the climate and the atmosphere and use the local life for a food source.

There may be very many worlds that resemble our Earth in some way; but few that resemble our planet sufficiently well to colonise without a lot of modification.

(either of ourselves or of the world concerned).

Jpax2003
2004-May-18, 07:31 PM
Hmm, OK if the earth is so rare and only an earth like planet can give rise to life, then would it then be more likely or less likely that such life would resemble terrestrial life? A good question, which has not yet been answered to my satisfaction is where did the mars sized impactor come from? Was it possible to have formed in this system and it just took a billion years to intersect with earth? What would have been the gravity dance it would have had with all the other bodies in the sol system? Could it have come from another system outside of sol system? Could it have been a large Kuiper belt type body, probably composed of mostly water ice? Could it have been another object hitting an object in our system causing it to crash into earth? Could some of the earth's co-orbital asteroids have been created by this impact, and could we determine this by probing and sampling these asteroids? Was the earth's orbital period changed by the impact? And if so, was it forced closer or farther?

George
2004-May-18, 08:48 PM
Extremophiles and thermophiles could survive on a planet which was not Earth-like; they may be common in the galaxy, depending on how life arises in the first place (not yet known).

Bacteria are amazing and prolific. Guns, Steel and Germs, as I recall, mentioned the possibility that bacteria constitute the largest organic mass of any one category, more than trees or animals.

However, 7 out of 10 nanobacteria interviewed will say the earth is extremely rare and should be cooked a little longer, at least until it stops quivering. :wink:



[I promise not to do that joke again]

Kaptain K
2004-May-19, 10:54 AM
A good question, which has not yet been answered to my satisfaction is where did the mars sized impactor come from? Was it possible to have formed in this system and it just took a billion years to intersect with earth?
It was much less than a billion years.

Ilya
2004-May-19, 07:07 PM
it has always seemed very unlikely to me that there will be many worlds in our galaxy where an unprotected human could step out of a spaceship and be able to tolerate the climate and the atmosphere and use the local life for a food source.

Hell, most of Earth does not fit this definition!

Jpax2003
2004-May-20, 05:11 AM
A good question, which has not yet been answered to my satisfaction is where did the mars sized impactor come from? Was it possible to have formed in this system and it just took a billion years to intersect with earth?
It was much less than a billion years.from which point in the formation of the sol system?

eburacum45
2004-May-20, 06:14 AM
it has always seemed very unlikely to me that there will be many worlds in our galaxy where an unprotected human could step out of a spaceship and be able to tolerate the climate and the atmosphere and use the local life for a food source.

Hell, most of Earth does not fit this definition!

Ha!

That's right; I keep forgetting that people cannot survive at the bottom of the oceans. Earth is a very hostile planet for the most part, but it is the best we have.

Dgennero
2004-May-20, 05:49 PM
I'd like to introduce one more thought that always amazes me: Compared to the life of stars, the universe is very young.
There haven't been hundreds of generations of stars; there was a first one, which created the heavier elements necessary to form rocky planets and lasted rather short (very hot stars), and then about two more generations of sun-like stars.
This could lead to two conclusions:

a.) If the earth is a rare occurence, it would make its existence as we know it even more stunning, since there was no time for countless generations of planetary systems to evolve, heightening the probability of occurrence of even a rare event.
b.) If however earth is a common planet, it would mean that life "routinely" evolves pretty fast (on a universal time scale).

We haven't found signs of another civilization so far (radio signals e.g.), and people in favor of a rare earth could use the young age of the universe as an argument that, since intelligent life as we know it seems not to be extremely common but still has evolved on a first or second generation planet, we have a rare earth phenomenon - it's like winning the jackpot on the first or second attempt.