Is there life in the universe, and if so has it visited Earth?

[Pythagorean]

However, it is a perplexing question to ask where and when did life first begin to emerge in the universe. And its not so far off the topic of this thread to ask this because, one would have to know these things in order to know when and how life "has visited Earth".

We can consider the time period we have to work with... 14 billion years... and the amount of material available to form life with... 10 to the power of 9... we still have to come up with the period during which life could form in the universe with proper conditions and relative stability for continued evolution etc...

I'm not the best at statistics and modeling but PF is probably the right place to ask this question..."what is the earliest period in the universe's development that life could begin to develop and where would that have been?"

This brings up another question that has always swam around when considering abiogenesis, too. Did life necessarily have to start in a single place?

Could there have been a period in a universe that was very conducive to the formation of life somewhat independent of space? Of course, there would still be a distribution of regions where it was more or less probable, but why is the question always asked from the standpoint that there's only one place of origin?

ADDENDUM:

Of course this doesn't mean that all these 'origin zones' were conducive to long-term development and evolution of their host life forms. Apparently (at least in the carbon-based model) we need something like Earth for that, where volcanoes and earthquakes serve to distribute nutrients about the surface of the planet.

 

[BoomBoom]

Very massive stars, exactly the ones who turn supernovae, are short lived. An extremely huge star can go supernova in a few hundred million years. So, the building blocks of life were possibly present in the first billion years of the universe.

Thanks Cel.
So, now how long would it take for those heavier elements to condense into new solar systems and the planets to cool to the point where abiogenesis could begin?

Then we can tack on a few billion years on top of that for life to evolve...

I'm just trying to get a sense of what the earliest possible point at which life could have evolved in the age of the universe.

 

[baywax]

Then we can tack on a few billion years on top of that for life to evolve...

Actually, with Earth being around 4.4 billion years old and the stromatolites that are thought to have been formed by some form of algae at around 3.5 billion years... it looks as though life only requires about a billion years to get to a point where it is mobile and constructive. This would mean that by about 500 million years into Earth's development there could have been a rudimentary form of life developed and evolving on earth.

In other words, with the proper conditions, you don't need "billions" of years for life to develop. This would dramatically push back the date of the first "emergences" of life in t he universe's "habitable zones".

(The plurals are for Pythagorean)

 

[BoomBoom]

This brings up another question that has always swam around when considering abiogenesis, too. Did life necessarily have to start in a single place?

If we really believe (well, many of us) that life forms so easily given the proper elements and conditions, then why is it that many assume it only happened once and all life on Earth came from a single source? If this is the case, then it should be happening all the time here on Earth IMO.

Craig Ventor is doing his ocean sequencing project where he is taking random samples from waters all around the world and sequencing the DNA recovered and I heard they are discovering incredible amounts of new genes not found in any other species (I can hunt down a link if required). Much of the microbial life of Earth could have come about more recently.

If this is not the case, and all life on Earth did come about by some freak accident, then I'd be much more skeptical about it existing elsewhere.


Ok, here's one article http://www.genomenewsnetwork.org/articles/2004/03/04/sargasso.php"

In the Sargasso Sea, they found 1800 species of microbes, including 150 new species of bacteria, and over 1.2 million new genes. Although they don’t know what most of these genes do, the research is a first step to understanding more about life in the Sargasso Sea and the larger ocean.

 

[BoomBoom]

This would mean that by about 500 million years into Earth's development there could have been a rudimentary form of life developed and evolving on earth.

In other words, with the proper conditions, you don't need "billions" of years for life to develop.

True, but I was putting this in the context and frame of reference of the original poll question, "...and if so, has it visited earth?".

For a life form to develope far enough to engage in space travel and travel to distant solar systems, I think it would be safe to assume that would take billions of years. In other words, how soon in the age of the universe could "intelligent" life have emerged?

 

[baywax]

For a life form to develope far enough to engage in space travel and travel to distant solar systems, I think it would be safe to assume that would take billions of years. In other words, how soon in the age of the universe could "intelligent" life have emerged?

For a virus, which can withstand the extremities of space, it would take as long as a virsus takes to develop... probably not billions but millions of years.

Intelligent life is not too far behind the development of rudimentary life forms. But you're right in that it would be around 3 billion years. However, if we look at whales as intelligent or primates with the ability to sign and recognize symbols etc... we can knock about 25 million years off the 2-3 billion.

So, we still need to know at what period during the development of the universe there were areas of stability and materials and conditions that would support life's origins.

 

[DaveC426913]

Intelligent life is not too far behind the development of rudimentary life forms. But you're right in that it would be around 3 billion years.

Which means they've could have been around for 10 billion years. Which poses the rather famous question:

So where are they?

 

[baywax]

Which means they've could have been around for 10 billion years. Which poses the rather famous question:

So where are they?

Actually we're trying to determine when, in the history of the universe, there were the proper conditions, materials and intervals for the first signs of life to develop in the universe.

This question will be answered partially if we know when the first supernovae were beginning to take place in the young universe.

Does anyone have the stats on that. I still haven't found any info on when the first supernovae started happening in the universe.

 

[DaveC426913]

Does anyone have the stats on that. I still haven't found any info on when the first supernovae started happening in the universe.

Look up "population III stars".

https://www.physicsforums.com/showthread.php?t=113668" that discusses at least the possibility of a Pop III star at a mere 900My after BB.

 

[BoomBoom]

Which means they've could have been around for 10 billion years. Which poses the rather famous question:

So where are they?

Intelligent life formed only 3.7B years after the BB? I think that is being VERY generous there.

We took nearly 5 billion years to arise and I would assume you could tack on a big chunk of time for the gases from the supernova we came from to condense into a new solar system...perhaps another billion or so?

As far as "where are they?":
Even giving the most optimistic assessments for the Drake equation, the nearest intelligent life could be 1,000+ LYs away. We have only been sending out signals that could be detected for 100 years or so. Chances are that an alien civilization wouldn't even be capable of detecting us for eons.

Then there is the other issue of whether or not interstellar travel is even physically possible in a reasonable span of time. So IMO the chance of aliens visiting Earth has got to be as close to 0% as you can get.

 

[baywax]

Look up "population III stars".

https://www.physicsforums.com/showthread.php?t=113668" that discusses at least the possibility of a Pop III star at a mere 900My after BB.

Thanks Dave.

This probability gives us about 13 billion years to develop life in the universe.

As we know, there are always spurts of development and evolution then catastrophes that can undo millions of years of evolution. Take for example the plight of the dinosaurids. So, with this factor in mind, we need to try to take down our expectations a fair amount to account for this phenomenon.
This is because a stable environment doesn't always stay stable.

 

[DaveC426913]

As far as "where are they?":
Even giving the most optimistic assessments for the Drake equation, the nearest intelligent life could be 1,000+ LYs away. We have only been sending out signals that could be detected for 100 years or so. Chances are that an alien civilization wouldn't even be capable of detecting us for eons.

Then there is the other issue of whether or not interstellar travel is even physically possible in a reasonable span of time. So IMO the chance of aliens visiting Earth has got to be as close to 0% as you can get.

The question though is: why have we not detected any radio or other leakage from them? They could be anywhere in the galaxy and, as long as they beat us to intelligence by a mere 100,000 years, we could detect them - if the signals were strong enough and if they weren't deliberately hiding.

 

[baywax]

The question though is: why have we not detected any radio or other leakage from them? They could be anywhere in the galaxy and, as long as they beat us to intelligence by a mere 100,000 years, we could detect them - if the signals were strong enough and if they weren't deliberately hiding.

Whether we've detected them or not may depend on the signals they're using. Could be very different technology like... micro waves or lasers or something that we either wouldn't look for or would miss completely.

 

[DaveC426913]

Whether we've detected them or not may depend on the signals they're using. Could be very different technology like... micro waves or lasers or something that we either wouldn't look for or would miss completely.

I suppose I forget just how darned big the sky is, and how big a light year is. It's not like they're going to have Christmas lights strung between the constellations.

 

[baywax]

I suppose I forget just how darned big the sky is, and how big a light year is. It's not like they're going to have Christmas lights strung between the constellations.

What are the possibilities of using laser to transmit info... and power even...?

 

[BoomBoom]

The question though is: why have we not detected any radio or other leakage from them? They could be anywhere in the galaxy and, as long as they beat us to intelligence by a mere 100,000 years, we could detect them - if the signals were strong enough and if they weren't deliberately hiding.

Good point. Although a mere billion years or so doesn't sound like much as far as the age of the universe is concerned, it is a VERY long time for a civilization to develope.

Even though the distances would probably be much to vast to send any type of signals back and forth (much less travel them), I would love to check out what they had on TV some 1000 years ago! :)

 

[Chronos]

The fact remains, there is no incontrovertable evidence 'aliens' have visited earth.

 

[CEL]

What are the possibilities of using laser to transmit info... and power even...?

The main reason laser is efficient in transmitting information is that the bean is focused in a narrow solid angle, instead of omni directionally.
If an alien civilization was deliberately trying to communicate with us, they could use a laser bean focused at our solar system, but this presuppose they know we are here and are interested in talking to us.
An omni directional transmission would spread its energy and soon become less powerful than the background noise.
Of course, if you use special codification, you can transmit and be detected with negative signal to noise (SN) ratios, but this assumes that the receiver knows the transmitted code.

 

[DaveC426913]

The main reason laser is efficient in transmitting information is that the bean is focused in a narrow solid angle, instead of omni directionally.
If an alien civilization was deliberately trying to communicate with us, they could use a laser bean focused at our solar system, but this presuppose they know we are here and are interested in talking to us.
An omni directional transmission would spread its energy and soon become less powerful than the background noise.
Of course, if you use special codification, you can transmit and be detected with negative signal to noise (SN) ratios, but this assumes that the receiver knows the transmitted code.

Not to contradict CEL, he may be an expert Legumications Specialist for all I know, but I have never found beans to be efficient over interstellar distances.



(Once is a typo, but twice is mock-worthy )

 

[CEL]

Not to contradict CEL, he may be an expert Legumications Specialist for all I know, but I have never found beans to be efficient over interstellar distances.



(Once is a typo, but twice is mock-worthy )

I stand corrected. But it is not polite to mock a foreigner for not spelling correctly your language.
Since I cannot edit my post, I ask the moderator to do this for me. I obviously meant beams not beans. Thanks.

 

[DaveC426913]

I stand corrected. But it is not polite to mock a foreigner for not spelling correctly your language.
Since I cannot edit my post, I ask the moderator to do this for me. I obviously meant beams not beans. Thanks.

Actually, your grammar and spelling are so good I had no idea English wasn't your first language. Otherwise I wouldn't have teased you. No hard feelings.

 

[CEL]

Actually, your grammar and spelling are so good I had no idea English wasn't your first language. Otherwise I wouldn't have teased you. No hard feelings.

Apologies accepted. I trust the spell checker to correct my writings, but since bean is an existing English word, of course the mistake was not detected.
By the way, I was born and live in Brazil.

 

[baywax]

The fact remains, there is no incontrovertable evidence 'aliens' have visited earth.

None have been identified. There are, however, two suspicious bits of evidence that aliens have visited here... on earth... Zapper Z's orchids and the humanoids with pointy heads in Vatican City.

 

[CEL]

None have been identified. There are, however, two suspicious bits of evidence that aliens have visited here... on earth... Zapper Z's orchids and the humanoids with pointy heads in Vatican City.

Could you please provide links for these evidences?

 

[baywax]

Could you please provide links for these evidences?

You can find Zapper's orchids in the "How Does Your Garden Grow?" thread.

Here's one pc of photo evidence of the pointy headed aliens... not sure but this one looks like Yoda...

http://www.spurgeon.org/images/pyromaniac/TeamPyro/b16.jpg

 

[CEL]

You can find Zapper's orchids in the "How Does Your Garden Grow?" thread.

Here's one pc of photo evidence of the pointy headed aliens... not sure but this one looks like Yoda...

http://www.spurgeon.org/images/pyromaniac/TeamPyro/b16.jpg

Good evidences.

 

[baywax]

Good evidences.

Yes but of what I'm not sure. Devil worship?

 

[baywax]

I see no reason to disbelieve that life exists elsewhere in the universe. The development of life is a relatively simple process that appears to require some mud, prions and nucleotides in a hot and turbulent environment. I don't think there is a shortage of this combination in the universe.

Whether extraterrestrial life has visited Earth or not is hard to prove beyond a doubt. If we are the product of extraterrestrial viral seeding or the intervention of some intergalactic travelers remains to be proven. Proving it will be difficult since we have no way of comparing life on Earth with life in another galaxy... as of yet.

Even if we find microbes on Mars, they may appear the same as terrestrial microbes because all microbes look the same. DNA matching may or may not help to distinguish between Mars microbes and Earth microbes. However, if Earth seeded Mars or Mars seeded Earth with microbes, in what way could this be demonstrated?

 

[DaveC426913]

Even if we find microbes on Mars, they may appear the same as terrestrial microbes because all microbes look the same. DNA matching may or may not help to distinguish between Mars microbes and Earth microbes. However, if Earth seeded Mars or Mars seeded Earth with microbes, in what way could this be demonstrated?

Gene mapping can tell us how divergent the two strains are. Finding strains on Mars that indicate they diverged from Earth life a billion years earlier than Earth had cooled would be a good indicator that Mars seeded Earth.

 

[baywax]

Gene mapping can tell us how divergent the two strains are. Finding strains on Mars that indicate they diverged from Earth life a billion years earlier than Earth had cooled would be a good indicator that Mars seeded Earth.

How do you date gene divergence?

 

[DaveC426913]

How do you date gene divergence?

Um. You got me there.

But I know that we can tell how long ago humans and chimps diverged (recent) versus humans and orangutans (less recent) or fungi and vertebrates diverged (a zillion years ago) based directly on the commonality of their genes.

 

[baywax]

Um. You got me there.

But I know that we can tell how long ago humans and chimps diverged (recent) versus humans and orangutans (less recent) or fungi and vertebrates diverged (a zillion years ago) based directly on the commonality of their genes.

Right. We are also finding new species and new gene pools today that we have never seen before... right here in the oceans of earth. When we compare these new genes to genes we theoretically find on Mars... and let's say there's a match... we still don't know if its the Martian egg or the Terrestrial chicken that came first since we don't know the age of the new genes. If there are only an estimated 4 billion new genes on Earth and 600 billion on Mars... this would indicate the population began there on the red planet.

But I still see what you're saying where commonality will play a part in identifying which came first.

But that's the easier scenario... comparing life on Earth to life from mars... because of the relative proximity. It is the "harder thing" when you try to match some dna on Earth to a galaxy like Andromeda.

By the way... Happy Independence Day!

 

[BoomBoom]

But that's the easier scenario... comparing life on Earth to life from mars... because of the relative proximity.

That would be working on the assumption that they would be related. Chances are if there is life on Mars, it would not share any genes with Earth life...any more than it would with life in Andromeda for that matter. If it did come up with any sort of match to earthly genes, that would be THE most compelling evidence for planetary life-transfer I think.

That said, I kind of doubt there is any life on Mars at all...just a hunch.

IMHO, I believe all the millions of "new" genes they are finding in the oceans that you mentioned that don't match to anything else may be new forms of life formed here on Earth.

http://www.jcvi.org/cms/research/projects/gos/overview/"

 

[baywax]

That would be working on the assumption that they would be related. Chances are if there is life on Mars, it would not share any genes with Earth life...any more than it would with life in Andromeda for that matter. If it did come up with any sort of match to earthly genes, that would be THE most compelling evidence for planetary life-transfer I think.

It would be very cool.

That said, I kind of doubt there is any life on Mars at all...just a hunch.

There's already some evidence that life "was" on Mars in this meteor...

http://nssdc.gsfc.nasa.gov/planetary/marslife.html

IMHO, I believe all the millions of "new" genes they are finding in the oceans that you mentioned that don't match to anything else may be new forms of life formed here on Earth.

I was speaking hypothetically, using the "new genes" as an example for a hypothetical comparative study.(comparing 4 billion genes found on Earth with an hypothetical 600 billion genes hypothetically found on mars.)

 

[BoomBoom]

There's already some evidence that life "was" on Mars in this meteor...

http://nssdc.gsfc.nasa.gov/planetary/marslife.html

It was my understanding that assertion had been debunked...or at least a lot of doubt anyways. Though it is possible it may have had some of the "building blocks" of life:

http://www.sciam.com/article.cfm?id=martian-meteorite-life-buliding-blocks"

I was speaking hypothetically, using the "new genes" as an example for a hypothetical comparative study.(comparing 4 billion genes found on Earth with an hypothetical 600 billion genes hypothetically found on mars.)

Not to be a pessimist, but 600 BILLION genes on Mars??! Surely you jest! :P


The reason I doubt it exists is based on what we know of the resiliency of life on earth. If it ever existed there, it should be there still in abundance...this does not seem to be the case. Seems to me there would be a better chance of life being on Venus than on Mars.

 

[baywax]

It was my understanding that assertion had been debunked...or at least a lot of doubt anyways. Though it is possible it may have had some of the "building blocks" of life:

http://www.sciam.com/article.cfm?id=martian-meteorite-life-buliding-blocks"





Not to be a pessimist, but 600 BILLION genes on Mars??! Surely you jest! :P


The reason I doubt it exists is based on what we know of the resiliency of life on earth. If it ever existed there, it should be there still in abundance...this does not seem to be the case. Seems to me there would be a better chance of life being on Venus than on Mars.

First of all its baywax, not Shirley! Second of all, life may be extinct or receding in abundance on Mars because a

Texas-Size Asteroid Slammed Early Mars, Studies Say

http://news.nationalgeographic.com/news/2008/06/080625-mars-impact.html

from the June 25/2008 edition.

Its always been obvious in the telescope that something very large (1000 to 1800 miles in diameter) hit Mars and popped its centre out the other side slightly while loosening most of the northern hemisphere's crust and sending it into orbit. Life likes living where there are still oceans and an atmosphere and both of these necessities left Mars the day this incident happened.

About the 600 billion genes, exaggeration is the stuff of hypothetical arrangements.

 

[baywax]

The first half of the question is answered more and more every time we discover a group of super Earth's in a distant solar system. The more we see planets similar to our own, the more we are going to be looking at the actuality of life taking place on planets other than earth.

 

[Ivan Seeking]

To clear up a few common misconceptions: David Morrison, interim director of NASA's Lunar Science Institute, has never seen a Martian. He has no idea what's in Area 51, the infamous place in Nevada where some people claim the government has captured and experimented on aliens, but he suspects it is merely a testing ground for aircraft. He has never seen a UFO, but he promises that NASA would tell us if a real one were spotted.

These are facts that Morrison explains on a daily basis to the readers of his column on the NASA website, "Ask an Astrobiologist." Formerly the director of astrobiology and space research at NASA's Ames Research Center in California, Morrison envisioned the column as a place for inquiring minds to ask about recent research—but instead has found himself having to disprove what seems like every Photoshopped-alien hoax that makes its way through cyberspace. He leaves readers' queries unedited so as to capture the nuances in questions such as: "I read some one elses question about rosewell, what is NASA hiding? the government is covering up something,i think we the american people should know. my question what are the NASA people dong in space so much? Mars and the moon could not be so interesting."

His reply? "Mars, the Moon, and the search for evidence of life beyond the Earth are indeed very interesting...They are far more interesting subjects than the fiction you refer to."
. . . .

http://www.usnews.com/articles/scie...earch-for-aliens-a-lot-of-dumb-questions.html

 

[engineroom]

Given the vastness of space I cannot rule out the existence of life on another planet. It is possible that life does exist and I don't think one has to believe in Creation or Evolution to accept the possibility, my argument is:

1) Creation: Just as God created Earth, Adam & Eve etc He would be free to create Paul & Jess and another planet somewhere else.

2) Evolution: If one believes in Evolution then one must believe in the basic scientific principle that anything is possible until proven not and no one has categorically proven life does not exist elsewhere in the Universe.

Whether alien life has visited Earth sometime in the eons of this planets existence is another matter and to that I have no answer other than I think it is possible but as yet unproven.

 

[CEL]

Given the vastness of space I cannot rule out the existence of life on another planet. It is possible that life does exist and I don't think one has to believe in Creation or Evolution to accept the possibility, my argument is:

1) Creation: Just as God created Earth, Adam & Eve etc He would be free to create Paul & Jess and another planet somewhere else.

2) Evolution: If one believes in Evolution then one must believe in the basic scientific principle that anything is possible until proven not and no one has categorically proven life does not exist elsewhere in the Universe.

Whether alien life has visited Earth sometime in the eons of this planets existence is another matter and to that I have no answer other than I think it is possible but as yet unproven.

Your reasoning is sound, but there is a confusion in it, that is common in creationists arguments, but not in this forum.
Evolution is a scientific theory that deals with how life has developed once it existed. The theory of how life arose from nonliving matter is called abiogenesis.
Evolution is solid, no matter if life began by abiogenesis, by divine intervention, or by seeding by aliens.

 

[DaveC426913]

the basic scientific principle that anything is possible until proven not

Sorry but this is not a scientific principle.


In fact, the most pertintent scientific principle might be Occam's razor: which model fits the facts with the least exceptions. Since there are zero facts indicating ET life, the implication would be that it's not out there until more compelling evidence shows otherwise.


Also, evolution has absolutely nothing to say about the creation of life on another planet. Evolution only acts on existing life. Evolution and creation are apples and oranges.

 

[D H]

Given the vastness of space I cannot rule out the existence of life on another planet.

We aren't talking about life here. We're talking about intelligent life. I would argue that even if primitive life is somewhat abundant, complex life will be rare and intelligent life, extremely rare. If the closest extant intelligent life is in some nearby galaxy or even more remote than that it doesn't really matter if that life exists. We are essentially alone.

If one believes in Evolution then one must believe in the basic scientific principle that anything is possible until proven not and no one has categorically proven life does not exist elsewhere in the Universe.

The first step is a non sequitur, the second clause is a falsehood, and the third clause is a red herring.

 

[baywax]

Yes, I think its a case of "if you say its out there you have to prove what you say" and not "I think its out there now prove me wrong". This is because when you make a statement as monumental as " there is life on 51 Pegasi" you don't just leave it up to someone else to prove it or to prove you wrong... you prove it for yourself and others.

So, get to work!

 

[D H]

Yes, I think its a case of "if you say its out there you have to prove what you say" and not "I think its out there now prove me wrong".

The first statement is a basic scientific principle. The second statement, which is essentially the same as engineroom's "the basic scientific principle that anything is possible until proven not" is the basic principle upon which crackpots operate.

Science underlying operating principles are similar to those of law. In both law and in science the burden of proof lies with the claimant. In both law and in science, placing the burden of proof on the claimant keeps claimants honest and helps reduce the number of frivolous claims.

 

[towerdp]

We aren't talking about life here. We're talking about intelligent life. I would argue that even if primitive life is somewhat abundant, complex life will be rare and intelligent life, extremely rare. If the closest extant intelligent life is in some nearby galaxy or even more remote than that it doesn't really matter if that life exists. We are essentially alone.


The first step is a non sequitur, the second clause is a falsehood, and the third clause is a red herring.

I would disagree with the fact that it would be rare to find "intelligent life" it struck twice on our planet. Us as humans have the ability to adapt and make somewhat sense of what's going on around us, and dolpins our other intelligent life form on Earth doesn't have the structure we do, but there brains are indeed intelligent. Like us they can be asked to create a new trick/movement that they have not been trained to do.

 

[Ivan Seeking]

2) Evolution: If one believes in Evolution then one must believe in the basic scientific principle that anything is possible until proven not

As stated already, you are way out of bounds with that one.

 

[D H]

I would disagree with the fact that it would be rare to find "intelligent life" it struck twice on our planet.

Dolphins, chimpanzees, and crows are all very smart, but do they qualify as "intelligent life"? It depends on your definition of "intelligent life". Do dolphin, chimpanzee, or crow have anything approaching the ability to receive signals from or send signals to other stars? Are there dolphin, chimpanzee, or crow cities? towns?? hamlets? Humans have been "intelligent life" for 5,000 years or so if intelligence is couched in terms of the demonstrated ability to form a civilization, and for less than 100 years if intelligence is couched in terms of the ability to receive signals from or send signals to other stars.

Dolphins and crows in fact exemplify the rarity of intelligent life. While they are very intelligent animals, their evolution has pushed them down a path that precludes the ability to advance beyond that stage.

The pre-conditions for life have to be right. Most star systems are inimical to life: they are too close to the galactic core, binary stars, or have hot jupiters. Of those that remain, an earth-like planet must form that escapes the run-away global warming of Venus thanks to a freak collision with a Mars-sized object and escapes the run-away cooling of Mars thanks to being a bit larger than Mars. Of those that remain, primitive life has to form and live through disasters such as the Late Bombardment. Of those that survive this, complex monocellular life has to form and escape its own pollution (Snowball Earth). Of those that survive this, multicellular life has to arise. Then pre-intelligence (dolphins, crows, hominids) has to arise. Then intelligence has to arise -- and not kill itself off. Intelligent life is, IMHO, exceptionally rare.

 

[vivesdn]

National Geographic november issue features some photos of The Cave of Crystals. On it, sveral crystals of selenite have grown up to 10m long and upt to two meters thick.
Conditions required: a cave in limestone, below water level, kept warm (112ºF) by an underlying magma chamber, undisturbed for hundreds of thousands of years.

Undisturbed: no water movement, no pH changes, no temperature changes, ..
And of course, water saturated on calcium sulphate. For 600000 years.

What would have been the probability of bus size crystals forming naturally?

Life on universe? That's easy? Intelligent? A matter of time.
Visited earth? This one is slightly more difficult.
Proofs? Not available (yet?).

 

[CEL]

...
What would have been the probability of bus size crystals forming naturally?
...

The probability of an event that has occurred is 1.

 

[Hanfonius]

I keep finding the words, 'The basic scientific principle that everything is possible until proven not.', and I cannot help but consider it accurate.

While it is misused in the sense of, 'I believe in UFO's - you prove me wrong.', how can it conceivably be wrong when used in the sense of, 'therefore, I shall attempt to prove it right, then present it to my peers for validation.'?

The von Daniken approach illustrates the former, and perhaps Gallileo the second.

The scientific mind must necessarily examine the unorthodox views of the day. Isn't that what most of us are doing right now in this section of the site?