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

[BoomBoom]

If we find life similar to that on Earth, the panspermia hypothesis will be reinforced.

Unless, of course, we find that the basic structure of life is universal.

However, any similar life we were to find in our solar system would have some claiming panspermia. So I guess we will have to find life outside our solar system that is similar to life on Earth to put that claim at rest? Or maybe that wouldn't do it either...maybe we need to find similar life outside our galaxy?

I guess since that theory (panspermia as the origin of life on earth) can never be proven or disproven, it will always be around...but it will never be anything more than pure speculation.

 

[The Dagda]

Unless, of course, we find that the basic structure of life is universal.

However, any similar life we were to find in our solar system would have some claiming panspermia. So I guess we will have to find life outside our solar system that is similar to life on Earth to put that claim at rest? Or maybe that wouldn't do it either...maybe we need to find similar life outside our galaxy?

I guess since that theory (panspermia as the origin of life on earth) can never be proven or disproven, it will always be around...but it will never be anything more than pure speculation.

If we find a load of humanoid races that are practically identical to us that might seal it, or The Greys tell us the truth or whatever. But let's face it we are unlikely to know possibly ever, but not never.

 

[baywax]

I guess since that theory (panspermia as the origin of life on earth) can never be proven or disproven, it will always be around...but it will never be anything more than pure speculation.

There must be a way to trace the origin of life with regard to abiogenesis vs panspermia. I think we've covered some methods using the configuration of a specimen's DNA or the single strand configuration of RNA and how it relates to the type of sunlight or mineral content in which it has evolved. Meteorites sporting apparent fossils tend to speak volumes about the relative ease life seems to have sprouting up in other regions of space.

 

[DaveC426913]

I guess since that theory (panspermia as the origin of life on earth) can never be proven or disproven, it will always be around...but it will never be anything more than pure speculation.

Of course it could be dis/proven (or at least satisafactorily resolved). It might take a fabulously advanced technology and knowledge base but, in principle, it's not much different from showing at Ebola arose out of an epicentre in Africa.

 

[Ivan Seeking]

Yes, there is no reason to think this can never be resolved. What's more, we could find a meteor containing alien bacteria, tomorrow.

 

[baywax]

Yes, there is no reason to think this can never be resolved. What's more, we could find a meteor containing alien bacteria, tomorrow.

Could it be determined if the meteor originated from an Earth impact or not?

 

[Ivan Seeking]

Could it be determined if the meteor originated from an Earth impact or not?

There may be situations where we couldn't be sure, but there are certainly indicators that would show it did not have terrestrial origins. For example, the meteor could be older than the earth. Or, we could find isotopic ratios not found on earth. Not my field but those are a couple of possiblities.

 

[CEL]

Unless, of course, we find that the basic structure of life is universal.

However, any similar life we were to find in our solar system would have some claiming panspermia. So I guess we will have to find life outside our solar system that is similar to life on Earth to put that claim at rest? Or maybe that wouldn't do it either...maybe we need to find similar life outside our galaxy?

I guess since that theory (panspermia as the origin of life on earth) can never be proven or disproven, it will always be around...but it will never be anything more than pure speculation.

There is no proof in empirical sciences. Observations are made, hypotheses derive from the observations and a theory is formulated. If subsequent observations confirm the theory, it is accepted. If in the future new observations don't fit the theory, it is reformulated or abandoned, but proof exists only in axiomatic sciences like Math or Logic.

 

[DaveC426913]

There is no proof in empirical sciences. Observations are made, hypotheses derive from the observations and a theory is formulated. If subsequent observations confirm the theory, it is accepted. If in the future new observations don't fit the theory, it is reformulated or abandoned, but proof exists only in axiomatic sciences like Math or Logic.

Well...

If we found a rock that had a markedly different composition from Earth, say it matched the composition of the Moon rocks to several decimals across a dozen elements, we can be pretty confident that rock is a meteorite.

You could bifurcate bunnies and claim "that's not proof" but frankly, if there's only one contender for theories and any other contender would require us throwing out centuries of well-established knowledge (such as: maybe it's a rock from a quarry that has an astonishingly coincidental elemental makeup to that of the Moon that heretofore has never been seen on Earth, and because, well, it's never been exposed to oxygen ... or water) then it's pretty much proven in my books.

 

[CEL]

Well...

If we found a rock that had a markedly different composition from Earth, say it matched the composition of the Moon rocks to several decimals across a dozen elements, we can be pretty confident that rock is a meteorite.

You could bifurcate bunnies and claim "that's not proof" but frankly, if there's only one contender for theories and any other contender would require us throwing out centuries of well-established knowledge (such as: maybe it's a rock from a quarry that has an astonishingly coincidental elemental makeup to that of the Moon that heretofore has never been seen on Earth, and because, well, it's never been exposed to oxygen ... or water) then it's pretty much proven in my books.

The only cases where you have only one contender to a theory is when this contender is the null hypothesis. In your example of a found rock: it is a meteorite or not. You can prove the null hypothesis if the rock was found in a quarry on Earth, where all he rocks have the same composition.
The hypothesis that it is really a meteorite cannot b proved, but we can accept it as very likely, in the case of an extraordinary match of its composition with that of a known extraterrestrial body. But very likely does not mean sure.

 

[The Dagda]

There is no proof in empirical sciences. Observations are made, hypotheses derive from the observations and a theory is formulated. If subsequent observations confirm the theory, it is accepted. If in the future new observations don't fit the theory, it is reformulated or abandoned, but proof exists only in axiomatic sciences like Math or Logic.

Just to be needlessly pedantic: math and logic are not really sciences unless they are applied to something real world. For example the death penalty why it is wrong, would be a sociological concern logical or not. And the aerodynamics of shuttle re-entry would be science, but n-dimensional topography may well be not, and neither is the ontological argument.

 

[baywax]

Well...

If we found a rock that had a markedly different composition from Earth, say it matched the composition of the Moon rocks to several decimals across a dozen elements, we can be pretty confident that rock is a meteorite.

You could bifurcate bunnies and claim "that's not proof" but frankly, if there's only one contender for theories and any other contender would require us throwing out centuries of well-established knowledge (such as: maybe it's a rock from a quarry that has an astonishingly coincidental elemental makeup to that of the Moon that heretofore has never been seen on Earth, and because, well, it's never been exposed to oxygen ... or water) then it's pretty much proven in my books.

Apparently its not that hard to tell the difference between terrestrial originating and extraterrestrial originating meteorites... from the Astrophysics Section..."When did H2O develop during the last 13.5 b y?"

On 28 September 1969, near the town of Murchison, Victoria in Australia, a bright fireball was observed to separate into three fragments before disappearing. A cloud of smoke and, 30 seconds later, a tremor was observed. Many specimens were found over an area larger than 13 km², with individual masses up to 7 kg; one, weighing 680 g, broke through a roof and fell in hay. The total collected mass exceeds 100 kg.

The meteorite belongs to the CM group of carbonaceous chondrites. Murchison is petrologic type 2, which means that it experienced extensive alteration by water-rich fluids on its parent body. before falling to Earth. CM chondrites, together with the CI group, are rich in carbon and are among the most chemically primitive meteorites in our collections. Like other CM chondrites, Murchison contains abundant CAIs. Over 100 amino acids (the basic components of biological life) have been identified in the meteorite. A 2008 study showed that the Murchison meteorite contains nucleobases. Measured carbon isotope ratios indicate a non-terrestrial origin for these compounds.

Measured purine and pyrimidine compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of 44.5% and +37.7%, respectively, indicate a non-terrestrial origin for these compounds. These new results demonstrate that organic compounds, which are components of the genetic code, were already present in the early solar system and may have played a key role in life's origin.

More recent dating sets its age at nearly 4.95 billion years; nearly 500 million years older than the age of the Earth.

The Murchison meteorite contains 12% water.

http://en.wikipedia.org/wiki/Murchison_meteorite

 

[DaveC426913]

Apparently its not that hard to tell the difference between terrestrial originating and extraterrestrial originating meteorites.

Yep. I was impressed when I first read about the uniqueness of the composition of extraterrestrial rocks.

 

[CEL]

This is interesting:
http://edition.cnn.com/2009/TECH/space/02/25/galaxy.planets.kepler/index.html

 

[Karl G.]

In Richard Dawkin's "The God Delusion", he argues that even if the probability of life occurring is extermely small (sorry, can't remember exact figures!), there still is a good probability that life exists somewhere else in the universe. Assume, for example, that there are 1,000 civilizations dispersed evenly throughout the universe. The distances between us and them would be so huge that (keeping relativity in mind and ignoring the slim possibility that large organisms can travel through worm-holes) communication and travel between any two civilizations would remain highly improbable, even if several of the civilizations where highly advanced compared to Earth. So the fact that foreign organisms have never visited Earth (I tend to believe all accounts of UFO's are spurious) doesn't mean they don't exist.

 

[Ivan Seeking]

I think you mean that all accounts of alien spacecraft s are spurious. People see UFOs every day.

 

[NWH]

I have three feelings on this matter. The first is my realistic opinion, what I think's realistically possible. The second is my back-up feeling, what I'd feel should the first be proved wrong. And the third is basically my fantasy...

1. Inteligent beings have not visited us, however the chances of them visiting us are greater than us visiting them. I don't believe there's any inteligent life near enough to us that we'd be able to view or observe from Earth or our solar system, other than micro-organisms. I think the amount of time involved in getting technology to a point of exploring anywhere outside of our own solar system, would take so long, it would probably never happen. If technology was ever possible to reach that kind of stage, I think it would be known to us by other beings from deeper in the universe who've had more time to develop and master the technology of intergalactic space travel. When concidering the fact that some galaxies are older than others, I'd imagine if inteligent life is around there, they'd probably do it before us. Once light drive is invented (if it ever is), that boundary is elimineted and the stars are open for exploration, which is why I believe whoever invents it first will be the one to make the visit and it won't be us.

2. Earth was inseminated by organisms hitching a ride on a commet which crash landed in the sea, bringing inteligent life into Earth's existence. I really like this idea, because in this instance, we'd be the visitors our selves.

3. Life in our solar system origionated from Mars. Sadly, they had to abandon their world because of being bombarded with asteroids from the near by exploding planet which created the asteroid field. With that, they fled to Earth and watched their planet continue to die, creating the Pyramids across the world as they colonised their new planet.

 

[CEL]

...
3. Life in our solar system origionated from Mars. Sadly, they had to abandon their world because of being bombarded with asteroids from the near by exploding planet which created the asteroid field. With that, they fled to Earth and watched their planet continue to die, creating the Pyramids across the world as they colonised their new planet.

Contrarily to popular belief, the asteroid belt is not the residue of an exploding planet, but the remains of matter insufficient to form a planet.
As for Mars, its gravity is insufficient to retain enough atmosphere, necessary to sustain intelligent life.

 

[Ivan Seeking]

As for Mars, its gravity is insufficient to retain enough atmosphere, necessary to sustain intelligent life.

Then why do we find NASA scientists who want to terraform Mars?

Perhaps you meant that the atmosphere wouldn't be sustainable long for intelligent life to evolve?

 

[harvellt]

Not that I agree life on Earth came from mars. I have seen some pretty credible people say that Mars could have sustained an atmosphere befor its iron core cooled and stopped spinning. Its not gravity alone that let's us keep our atmosphere but also the magnetosphere that prevents it from beeing torn off by the solor winds.

 

[Ivan Seeking]

Its not gravity alone that let's us keep our atmosphere but also the magnetosphere that prevents it from beeing torn off by the solor winds.

True. There was a discussion about this some time ago. IIRC, Mars could have had an atmosphere for a couple of billion years. But even if I am remembering this correctly, it may be a subject of debate.

 

[NWH]

Contrarily to popular belief, the asteroid belt is not the residue of an exploding planet, but the remains of matter insufficient to form a planet.
As for Mars, its gravity is insufficient to retain enough atmosphere, necessary to sustain intelligent life.

Yeah, that's why I said it's more of a fantasy than my actual realistic opinion. I just like the idea that our solar system was vastly different to how we imagine and that inteligent life might have existed before us. But yeah, the first point I made was pretty much how I see things.

 

[baywax]

Then why do we find NASA scientists who want to terraform Mars?

Perhaps you meant that the atmosphere wouldn't be sustainable long for intelligent life to evolve?

Did Mars lose atmosphere, oceans and gravity (including the detriment of its core) after being hit so badly that it lost half its crust and was practically run through by an impact?

 

[harvellt]

From what I understand, can't have less gravity unless you have less mass. Also Mars is smaller than Earth so the core cooled faster and solidified.

 

[DaveC426913]

From what I understand, can't have less gravity unless you have less mass.

Depends. You can have less surface gravity if the body is larger.

Gliese 581c is five times more massive than Earth but its surface gravity is only a little more than 2x Earth's because Gliese's radius is 1.5x Earth's.

i.e. for a given mass, surface gravity can vary depending on the density (and thus radius) of the body.

That may or may not factor into Mars, I'm merely pointing out that mass(p) =/= gravity(p).

 

[harvellt]

Ahh yea makes perfect sense but you would need to change the density of the sphear of a planet and I am not sure how this could have happened on mars.

 

[Ivan Seeking]

At the least, it takes on the order of a billion years for the atmosphere to be blown away by the solar winds. It isn't like the atmosphere just floats away.

 

[baywax]

How Mars Lost its Atmosphere
15 April 1989

ASTEROIDS and comets have blasted away most of Mars's original atmosphere, according to new calculations made at the University of Arizona, in Tucson. The new results contradict earlier ideas that comets may have built up the water and atmosphere on planets in their early days.

Jay Melosh and Ann Vickery have looked at what happens to a planet's atmosphere when a comet or asteroid strikes the surface. Other researchers found that solid fragments from the explosion could push a negligible amount of the gases into space. Melosh and Vickery have now discovered a much more important effect (Nature, vol 338, p 487).

When an object hits the planet, it explodes into a plume of hot gases that can expand faster than the planet's escape velocity. This gas sweeps up the surrounding gas in the atmosphere, and lifts it into space.

The process is most efficient when the planet has a low gravity, so an object that hits Mars, which is a small planet, would need to be only 3 kilometres across, to sweep the gas up, while for the Earth we would need something 13 kilometres in diameter to produce the same effect.

Melosh and Vickery suggest that Mars originally had an atmosphere with a pressure similar to that of Earth. At present the atmospheric pressure of Mars is only 1/150th that of the Earth.

http://www.newscientist.com/article/mg12216603.400-science-how-mars-lost-its-atmosphere-.html



And about Mars' crust/core...

The interior of Mars appears to contain a dense core of about 3,400 km (2,200 miles) in diameter, a molten rocky mantle somewhat denser than the Earth's, and a thin crust. The crust is about 80 km (50 miles) thick in the southern hemisphere but only about 35 km (22 miles) thick in the north. Mars' relatively low density compared to the other terrestrial planets indicates that its core probably contains a relatively large fraction of sulfur in addition to iron (i.e., as iron sulfide).

Although scientists now believe that the planet's core still has liquid molten iron in an outer layer, they are uncertain whether the inner core solidified like Earth's (more). Mars appears to lack active plate tectonics and volcanic activity at present like Mercury and Earth's Moon. Large but weak, and not global, magnetic fields exist in various regions of Mars which are probably remnants of an earlier global field that has since disappeared.

http://www.solstation.com/stars/mars.htm

I'd suspect that the loss of half of the northern hemispheric crust of Mars due to a more recent super-sized impact event would reduce an already weaker gravitational environment. You can see in these statistics that Mars' crust in the southern hemisphere is about 50 miles thick and in the north appears to be more than 50% less in thickness. Please feel free to calculate how much mass was lost during the impact event.

 

[phyzmatix]

As for Mars, its gravity is insufficient to retain enough atmosphere, necessary to sustain intelligent life.

...as we know it...

 

[Ivan Seeking]

The building blocks of life may be more than merely common in the cosmos. Humans and aliens could share a common genetic foundation.

That's the tantalizing implication of a pattern found in the formation of amino acids in meteorites, deep-sea hydrothermal vents, and simulations of primordial Earth. The pattern appears to follow basic thermodynamic laws, applicable throughout the known universe.

"This may implicate a universal structure of the first genetic codes anywhere," said astrophysicist Ralph Pudritz of McMaster University in Hamilton, Ontario...

http://blog.wired.com/wiredscience/2009/04/thermodynamino.html

Preprint
A thermodynamic basis for prebiotic amino acid synthesis and the nature of the first genetic code
http://arxiv.org/abs/0904.0402

 

[GODISMYSHADOW]

You mustn't ask a question like, "Is there life beyond our planet?"
Here's a better question: "Is there life beyond our planet within
500 light-years?" Put some limits on it.

 

[Blenton]

You mustn't ask a question like, "Is there life beyond our planet?"
Here's a better question: "Is there life beyond our planet within
500 light-years?" Put some limits on it.

What difference does it make? Honestly if they haven't found faster than light travel then that pretty much limits them effectively reaching us in this solar system only. If they do have FTL travel then who is to say that they can't travel 1 light year as easily as 500.

 

[GODISMYSHADOW]

What difference does it make? Honestly if they haven't found faster than light travel then that pretty much limits them effectively reaching us in this solar system only. If they do have FTL travel then who is to say that they can't travel 1 light year as easily as 500.

For a measured region of space, like within 500 light-years of Earth, there could be a definite
yes or no answer. For unlimited space you can't say there's not, so why even ask?

 

[ibcnunabit]

The answer in the poll that I would have preferred would be "possibly, but I doubt it."
I'd almost say no, but there's always that chance that it's happened and we never knew, so I felt compelled to say "maybe/maybe not."

 

[Vectus]

Wow, just got done reading this thread.


I saw a couple times mentioned the possible reasons why we have not yet encountered a technological civilization yet, given that the evidence we have and what we know suggests that such should be commonplace in the universe and a sufficiently advanced civilization could colonize the galaxy on the order of less than a million years.

I believe the reasons cited were 1) That such civilizations do not exist [or may not exist simultaneously](i.e. - intelligent life capable of producing said civilizations are either extremely rare or inherently self destructive), 2) That interstellar travel or communication is not feasible for any civilization due to the massive scale of time and space, and (as pointed out by Dave) 3) They may be there but intentionally avoid contact with us.

I just wanted to add a 4th since I haven't seen the idea discussed any:

They may not want or need to colonize other planets.