Evidence for ET is mounting daily, but not proven.

[Trakar]

This is the point of the green dog joke. We have no evidence that green dogs exist, but if they do, they are more likely to enter a house with an open door than a house with a closed door. Similarly we have no evidence that ET life exists, but if it is to be found, it seems most likely that it will be found on Earthlike worlds...

Primary problem I see with this currently, is that "Earthlike" in its current usage is entirely too broad and unlikely to provide a useful correlation to "habitable." To my considerations a useful definition of earthlike/habitable should exclude planets like Mars, Venus, or any other planetary environment where its parameters are in excess of +/- 10% of Earth normal, at least until we have observations and evidences that such situations are indeed (or compellingly probable to be) earthlike and habitable.

[Paul Wally]

The observer can only say if there is oxygen; he cannot say if it was generated by life (and therefore evidence of life) or not generated by life (and therefore not evidence of life).

The observer (scientist) can however pose the hypothesis that the oxygen is generated by life. Another observer may pose a different hypothesis (perhaps a geological explanation) to explain the same oxygen. This is then where a scientific debate starts between the two hypotheses (tentative assertions), where both parties cite evidence and arguments supporting their respective theories. So in this sense, the same evidence can be evidence for different conflicting hypotheses. It is however unfortunate that we don't get to an actual scientific discussion but get stuck on what ontological commitment to make on the issue of ET life. No such commitment is however needed to proceed in discussion of possibilities.

[Colin Robinson]

The observer (scientist) can however pose the hypothesis that the oxygen is generated by life. Another observer may pose a different hypothesis (perhaps a geological explanation) to explain the same oxygen. This is then where a scientific debate starts between the two hypotheses (tentative assertions), where both parties cite evidence and arguments supporting their respective theories. So in this sense, the same evidence can be evidence for different conflicting hypotheses.

Well said.

In a situation like this, neither of the two hypotheses is an established fact, and yet neither is merely a speculation. Formulating and testing hypotheses is what science is all about.

For instance the discovery of methane in the atmosphere of Mars prompted planetary scientists to look at at least three hypotheses. Apart from the two already mentioned in this thread (a geothermal process, or a small population of micro-organisms), another one was supply of methane from meteorites. As I understand it, the meteorite hypothesis has been discounted, because calculations showed it is not consistent with the quantitative evidence.

[Selfsim]

It is however unfortunate that we don't get to an actual scientific discussion but get stuck on what ontological commitment to make on the issue of ET life.

…

For instance the discovery of methane in the atmosphere of Mars prompted planetary scientists to look at at least three hypotheses. Apart from the two already mentioned in this thread (a geothermal process, or a small population of micro-organisms), another one was supply of methane from meteorites. As I understand it, the meteorite hypothesis has been discounted, because calculations showed it is not consistent with the quantitative evidence.

So, Curiosity has a Tunable Laser Spectrometer capable of assessing the C3/C4 isotopic ratio of CO₂ and Methane. (Which can be used to determine organic/inorganic origins). This ratio works on Earth (to certain degrees), but will it work for Mars samples ? … Ie: are our prior measurement assumptions valid, or not ?).
Its interesting to note that even with such an accurate instrument, it would be unlikely that life could be declared on the basis of this sole measurement alone. Even some Earth-life samples don't necessarily result in a conclusive 'life' determination .. and that's even if we already we know, (by other means), that the sample does contain living organisms.
I also find it a little surprising that a microscope doesn't seem to have been included with the analysis package.

Regards

[mutleyeng]

well, i dont think anyone has any expectations of life being declared with the curiosity mission.
Ive got no idea what NASAs plans are now to follow curiosity.
Hopefully the russians will rescue exomars. If not, we will maybe have to wait a long time.

[Paul Wally]

…

So, Curiosity has a Tunable Laser Spectrometer capable of assessing the C3/C4 isotopic ratio of CO₂ and Methane. (Which can be used to determine organic/inorganic origins). This ratio works on Earth (to certain degrees), but will it work for Mars samples ? … Ie: are our prior measurement assumptions valid, or not ?).
Its interesting to note that even with such an accurate instrument, it would be unlikely that life could be declared on the basis of this sole measurement alone. Even some Earth-life samples don't necessarily result in a conclusive 'life' determination .. and that's even if we already we know, (by other means), that the sample does contain living organisms.
I also find it a little surprising that a microscope doesn't seem to have been included with the analysis package.

Regards

Theory-ladenness of measurement procedure is a valid concern, but in the event that such a measurement yields a positive result it's always possible to follow it up with a different kind of measurement (e.g. with a microscope) to get more conclusive results, therefore at the same time testing the "prior measurement assumptions".
In the event that the prior measurement assumptions turn out to be correct it helped to identify a test sample, but if it turns out to be wrong then of course revision of those assumptions must be considered.

[Jeff Root]

Which is why NOBODY has said that it is evidence of ET life.

On the other hand, it IS evidence FOR ET life. That is, it is
evidence which supports the expectation of ET life.

I'm not disagreeing with you, but this is analogous to saying
that the ownership of guns is evidence for murder. If people
own guns then there is a good chance that murder will occur;
but if no-one uses the guns then there will be no murder.

I'm not going to analyze this analogy. It is bad enough that
KABOOM may have murdered someone in order to illustrate what
evidence is. Nobody said a gun was involved.

Please think up a different analogy. Preferably nonviolent
and nonpolitical.

If life does not occur on any of these potentially habitable
worlds then the expectation of life is a false one.

What does that mean? What is a false expectation?

If you expect something to happen and it doesn't happen, was
your expectation false?

For example, if you expect it to rain tomorrow, based on the
weather prediction you saw this morning, and it doesn't rain,
does that mean your expectation was false?

Any expectation can fail that way. Discovering that life does
not occur on some potentially habitable worlds doesn't make the
expectation of life there more "false" than your expectation
that it will rain tomorrow if it turns out not to rain.

-- Jeff, in Minneapolis

[Jeff Root]

"An observation consistent with something" is not a
definition of evidence. It simply means there is no
contradiction between the two.

I agree that that is not a definition of evidence.
Not even remotely close.

To count as evidence, the observation has to actively
support the hypothesis.

I don't know what you mean by "actively", but it is a
tautology to say that an observation which supports an
hypothesis is evidence for that hypothesis.

Last night, Matilda's Cake Shop was robbed. Police want a
speedy result, so they've arrested local man Michael Jenkins.

If Jenkins was staying with friends 100 miles away at the
time of the robbery, that would be evidence that he did not
rob the shop. It's not proof, but it is evidence.

But if Jenkins was at home at the time of the robbery, would
this be evidence that he did rob the shop? Of course not!
It's merely consistent with the police's belief, not
supportive of it.

If Jenkins was at home at the time of the robbery, it is
obviously evidence that he did not rob the shop. On the
other hand, if Jenkins was seen near the shop shortly before
the robbery, that is obviously evidence supportive of the
hypothesis that he did rob it.

There's a lot of fruitless quibbling over prepositions
going on in this thread - "for" and "of".

Your argument appears to be that prepositions with 2/3
of their letters in common have pretty much the same
meaning, so "of" and "for" can be used interchangeably.

I say "for", you insist I said "of". Over and over.
So I repeat what I said and show how it differs from
what you claim I said. Over and over.

A more important matter is being overlooked - that there
is a neutral ground where things are neither evidence for
nor against a hypothesis.

That obvious fact may not have been mentioned previously
because it doesn't resolve the controversy. The vast majority
of observations -- pieces of evidence -- are not relevant to the
question at hand. They are neither evidence for nor against the
hypothesis that life is abundant in the Universe. The color of
my toothbrush handle is pretty obviously one such.

But the assertion in the thread title is that some of the
observations made in recent years, and ongoing, do support the
hypothesis that life is abundant in the Universe. Even though
they do not include any identifiable observations OF life in
places other than Earth. Discovery of extrasolar planets,
liquid-driven geological processes on Titan, probable liquid
water on other moons, geothermal activity on moons, organic
molecules in space, vast numbers of chemical processes which
could produce complex molecules in a wide variety of natural
conditions, are all evidence which support the hypothesis that
life is abundant in the Universe. The rate at which this
evidence is being added to is increasing almost constantly,
and has been doing so for pretty much my entire lifetime.

I'm not asking you to believe that the evidence makes the
case for ET life, but I *am* asking you to quit claiming that
it somehow isn't evidence, or isn't relevant. That is just
absurdly wrong.

An Earth-sized planet found in a star's habitable zone
occupies this neutral ground. Its existence is consistent
with a universe teeming with life; its existence is equally
consistent with a universe in which no life exists beyond
Earth's atmosphere.

I agree. Up to that point.

That's what I call "not evidence".

It is evidence. Evidence which supports the hypothesis that
there is ET life. It is not neutral.

However, I will admit that I do not know how to argue the
point. I have struggled to come up with an argument and have
not been able to. Maybe another participant in the thread can
think of something. So as it stands it is just my assertion
against yours. I have not made a case for my side, and you
have not made a case for yours.

-- Jeff, in Minneapolis

[Jeff Root]

Strange,

Your reply #838 satisfies me. I wrote this before I saw it.
So now it's mainly for Paul. I was replying to your post #835:

If there is a problem with my logic, I would love to see it.

Modus ponens gives a deduction from definite premises:

If P, then Q.
P.
Therefore, Q.

But you are saying:
If P, then Q.
P.
Therefore, R.

where:
Q=possibility of life
R = life exists

Or to put it another way
If P, then maybe Q.
P.
Therefore, Q.

Your last line should be: Therefore, maybe Q.

Additional observations:

Paul brought up modus ponens. Since he's said no more about it
I don't know whether that is the logical form he meant or not.
Either way, I never claimed any deduction of mine had or was
intended to have that form or any other form. Further, I don't
recall posting sufficient info in this thread to determine the
form of logic I used in any argument, so unless you say which
statements of mine you claim I used in one of the invalid forms
you posted, I have no way of knowing what you are referring to.

I have not posted an argument supporting my certainty that there
must be life all over the Universe. You appear to say that I
have. So I want to know which statements you're referring to.

-- Jeff, in Minneapolis

[Jeff Root]

Every time that 'of/for' reference was made I groaned.

Do you agree with Paul that the terms are synonymous?

-- Jeff, in Minneapolis

[Jeff Root]

Which is why NOBODY has said that it is evidence of ET life.

On the other hand, it IS evidence FOR ET life. That is, it is
evidence which supports the expectation of ET life.

This is the point of the green dog joke. We have no evidence
that green dogs exist, but if they do, they are more likely
to enter a house with an open door than a house with a closed
door. Similarly we have no evidence that ET life exists, but
if it is to be found, it seems most likely that it will be
found on Earthlike worlds.

Yes, I understand. It is relevant as a joke, but doesn't tell
us anything useful about the assertion in the thread title that
evidence for ET is mounting.

It's pretty clear that green dogs can only exist in houses with
open doors: Life can only exist in places that have matter and
a flow of energy, within some temperature limits...

Open doors are not evidence for or of green dogs.

We start out not knowing whether there are any houses with open
doors other than the one we live in. When we discover evidence
that there are lots of houses, some of which look like they may
have open doors, we have evidence that green dogs can exist in
places other than our house.

That evidence supports the hypothesis that green dogs do exist.
The question then is: What other evidence is available?

As I said before, the preposition thing is a fruitless quibble
- and I'm speaking as someone who teaches grammar for a living.

So you believe that "of" and "for" are essentially synonymous?
They can be used interchangeably? Or what? Why do you insist
on equating "of" with "for"?

Evidence for/of ET should be restricted to phenomena that is
best explained by ET, not by things that could possibly maybe
at a stretch be ET, and not by things that would make for a
fairly comfortable environment for life as we know it.

Evidence is evidence. You don't get to put restrictions on it.

If you know of a place where life might be, but the evidence is
that there are no stars or planets or significant amounts of
matter there, then that is evidence AGAINST life in that place.

Yes.

If you find that there is a star in that place, that is
evidence FOR life there.

No it is not. Absence of evidence against something does not
translate to evidence for something.

If a star is required for life, then the presence of a star in
a place is evidence supporting the hypothesis that life exists
in that place.

If you find that the planet is in the "habitable zone", it is
evidence FOR life there.

Ditto. I see the house with the open door; I do not see the
green dog.

If you find that the planet has an oxygen-rich atmosphere, it
is evidence FOR life there.

Now that is a horse of an entirely different breed, because it
is unlikely that a lifeless planet would have an oxygen-rich
atmosphere.

You make it clear that you think the only evidence which
supports an hypothesis is evidence which was caused by the
subject of the hypothesis.

Maybe that oxygen was generated by life. If it was generated
by life, then the oxygen is evidence OF life there. If it was
not generated by life, then the oxygen is NOT evidence OF life
there. But whether the oxygen was generated by life or not,
until we know whether life exists there or not, the oxygen IS
evidence FOR life in that place.

More backward logic. (Or something else is backwards.)

Nothing is backwards. It is practically a tautology.

The observer can only say if there is oxygen; he cannot say
if it was generated by life (and therefore evidence of life)
or not generated by life (and therefore not evidence of life).

That's part of what I just said. Obviously.

Which is why NOBODY HAS DONE SO.

Done what?

Called evidence of possible habitability "evidence of life",
which was clear from the context of my reply to Luckmeister
from which you took the quote.

-- Jeff, in Minneapolis

[Jeff Root]

The illustration shows -- in a very minimalist way -- how
evidence works, in the hope that you will get it.

You've still not explained what it has to do with this thread.

Yes I have.

The Drake equation does not calculate odds. It never has and
never will. It is not useful for calculating odds, even roughly.
It is a tool for thinking about the possibilities and analyzing the
requirements for life in the Universe.

Odds and possibilities are the same thing.

You know nothing about the subject.

It would be reasonable to say that odds and probabilities
are the same thing. Possibilities are not probabilities.
They are different words which refer to different things.

'Is it possible....yes....well how posible is it....let's
use this equation'

You know nothing about the Drake equation. If you did, you
would know that it cannot be used to calculate probabilities.

The very point of drakes equation is to show the range of
potentially intelligent species in the galaxy. That's why it
exists. Not calculate odds? That's it's very modus operandi.

No, you know nothing about the Drake equation. Its purpose
is to show what factors might determine the prevalence or
otherwise of intelligent life in the galaxy. More specifically,
it is a guide for scientific speculation about those factors.
It is a very useful tool for that purpose. It is useless
for calculating odds.

I'll repeat it yet again.

Evidence of habitability is evidence of habitability

It's not evidence for life.

There is no reason why it shouldn't be. Nothing prevents it
from being evidence for life.

We can not infer life from habitability based on a sample
of 1. It's unscientific and untenable to do so. It's also
dishonest and misleading.

And you know perfectly well that I am doing no such thing.

As I said, vastly more is already known about the Universe
than is dreamt of in a philosophy based on the assumption
that we only have a single data point from which to work.

-- Jeff, in Minneapolis

[Swift]

You know nothing about the subject.

...

You know nothing about the Drake equation.

Jeff Root and everyone else

Take it down a notch. If you all can not discuss this topic politely, it won't be discussed at all. Stop with the rudeness and the "yes it is", "no it isn't".

[Strange]

Your argument appears to be that prepositions with 2/3
of their letters in common have pretty much the same
meaning, so "of" and "for" can be used interchangeably.

In this context, the meaning is identical for me. Maybe your dialect/idiolect is different but I didn't even see that your were trying to say two different things until you had repeated it several times. I just thought you were saying "it is not evidence of life but it is evidence of life".

(And, obviously, it has nothing to do with the letters in the two prepositions )

ETA: Just catching up, but I think that answers your question in post #849 as well.

[Paul Beardsley]

I really don't have the energy to attempt to untangle the errors in post 851, but perhaps it will clarify things if I say this:

If "evidence for ET life" has any meaning distinct from "evidence of ET life", it seems to be a contraction of "evidence of things we think are needed for ET life to exist", although frankly I'd rather people just said that, as the contracted form is ambiguous and misleading.

And that's what we've got so far. We've found things that we think life needs. There may well be other things that life needs that we don't yet know about, and which we might or might not find. It might be that all the elements are available but life just doesn't happen anyway. It might be that life arises in most cases of the elements being available. We just don't know.

[djellison]

As I said, vastly more is already known about the Universe
than is dreamt of in a philosophy based on the assumption
that we only have a single data point from which to work.
s

How many data points do we have, exactly?

And thus what are your values for

fℓ = the fraction of the habitable planets that actually go on to develop life at some point
fi = the fraction of the above that actually go on to develop intelligent life


My take - there is no value (apart from the fact that is must be >0 ) that is 'known'. We simply do not know. To say otherwise isn't honest or scientific.

[Colin Robinson]

How many data points do we have, exactly?

And thus what are your values for

fℓ = the fraction of the habitable planets that actually go on to develop life at some point
fi = the fraction of the above that actually go on to develop intelligent life


My take - there is no value (apart from the fact that is must be >0 ) that is 'known'. We simply do not know.

The article that started off this thread was about prospects for some sort of life beyond Earth, not necessarily intelligent life. Many of the terms of the Drake equation, like the frequency of intelligence evolving, are irrelevant to the question of life as such.

It's an important distinction, because it is quite possible to be pessimistic about extraterrestrial intelligence, or even about active multicellular life, yet optimistic about the prevalence of extraterrestrial life in general. This (as I understand) is the view taken by scientists who support the Rare Earth Hypothesis.

But you're right -- we don't yet know the value for f(L), the probability of life emerging on a habitable world. It is still a matter of opinion -- informed, scientific opinion. There is still no proof.

That is the single clue we still need, before we could conclude beyond reasonable doubt that life in the universe is indeed widespread. We need either

* an example of an organism sufficiently different chemically as to demonstrate a second abiogenesis. OR
* an account of abiogenesis (e.g. based on archeological evidence and laboratory modelling) that is rigorous enough to assign a probability value for f(L).

These are clues we can look for now, within our own solar system. And yet, if we find either of these clues, we'll be able to safely conclude that life does exist on numerous worlds through the Galaxy.

[Jeff Root]

Your argument appears to be that prepositions with 2/3
of their letters in common have pretty much the same
meaning, so "of" and "for" can be used interchangeably.

In this context, the meaning is identical for me.

Well, that's interesting. I don't quite see how that is
possible, but their meanings are harder to define than
visualizable words like "to" and "from".

Maybe your dialect/idiolect is different but I didn't even
see that your were trying to say two different things until
you had repeated it several times. I just thought you were
saying "it is not evidence of life but it is evidence of life".

The first two words of the thread title are "Evidence for".
I first pointed out the difference in post #104, way back
in December 2010:

The thread title says "Evidence for ET is mounting". That is
exactly correct. It does not say "Evidence of ET is mounting".
That would almost certainly be incorrect. It is remotely
possible that some of the data that has been collected so
far actually does include evidence of ET's, but if so, it is not
apparent.

If the two words had completely different sets of letters,
I'm sure there would be no confusion.

-- Jeff, in Minneapolis

[Jeff Root]

I really don't have the energy to attempt to untangle
the errors in post 851, but perhaps it will clarify things
if I say this:

If "evidence for ET life" has any meaning distinct from
"evidence of ET life", it seems to be a contraction of
"evidence of things we think are needed for ET life to
exist", although frankly I'd rather people just said that,
as the contracted form is ambiguous and misleading.

The thing is, it's the title of the thread. And I had no
trouble distinguishing between the two words.

-- Jeff, in Minneapolis

[Jeff Root]

As I said, vastly more is already known about the Universe
than is dreamt of in a philosophy based on the assumption
that we only have a single data point from which to work.

How many data points do we have, exactly?

How many things do you know about the way the
Universe works? How many things are known by all
of mankind? That many.

And thus what are your values for

fℓ = the fraction of the habitable planets that actually
go on to develop life at some point
fi = the fraction of the above that actually go on to
develop intelligent life


My take - there is no value (apart from the fact that it
must be >0 ) that is 'known'. We simply do not know.

I agree. I wouldn't put any specific values to those
variables, and you should know that from what I just
said to you.

To say otherwise isn't honest or scientific.

To say that we do know values for those variables
wouldn't be honest. To say that all we know about
them is that they must be greater than zero would
be just as dishonest. We know a great deal about
how the Universe works, including life. From that
knowledge we can deduce a great deal more.

-- Jeff, in Minneapolis

[Paul Beardsley]

The thing is, it's the title of the thread. And I had no
trouble distinguishing between the two words.

Okay, two questions:

1. Do you confirm that your interpretation of "evidence for ET" is "evidence of things we think are needed for ET to exist"?

2. What do you think "but not proven" means in the title? That we don't have proof of ET, or we don't have proof for ET? I don't think there's any real doubt about the extrasolar planets and so on, so why say "but not proven"?

[djellison]

To say that all we know about
them is that they must be greater than zero would
be just as dishonest. We know a great deal about
how the Universe works, including life. From that
knowledge we can deduce a great deal more.

Then bring that knowledge to the table. What's scientific data constrains those all important variables? You've twice refereed to this 'knowledge'. What is it.

We have only one rock in the entire universe where we have observed life to have evolved. One.

It's one data point Jeff. No more. No less.

If you believe other data more tightly constrains those values - then show it.

[Strange]

The thing is, it's the title of the thread. And I had no
trouble distinguishing between the two words.

I don't think any of us have a problem distinguishing the words. The question is more about the semantics of the sentence.

For at least some of us, it would have made no difference at all if the title had used "of".

Prepositions are one of the most variable bits of language and I don't know if this distinction (or lack of) is a purely personal thing, or reflects a US/UK usage difference (or even, Minneapolis vs rest of the world ).

[eburacum45]

Another way to look at the premise of the OP is to consider whether 'evidence' 'for' life really is mounting daily.

In some ways I don't think this can be supported. Certainly we are aware of many more planets and planetary systems than we were back when Carl Sagan was alive. But the planets and planetary systems that are currently being detected are quite different to the Solar System and its planets; we can't suppose (like Sagan once did) that every planetary system might have about two potentially habitable planets. A large proportion of the systems discovered so far probably have no room for any potentially habitable planets, and the Solar System is not typical; only 10% or so of planetary systems may be like ours, with terrestrials in the inner system and gas giants in the outer part. The rest are quite different, often full of eccentric (or retrograde!) planets.

Personally I think life can probably emerge in a far wider range of environments than just Earth-like ones; but I have no evidence of this (or for it).

We also have no direct evidence to present concerning the frequency with which life emerges in any environment, Earth-like or otherwise. There is indirect evidence, though; the period between the cooling of the Earth's surface layers and the emergence of life-related phenomena is relatively short, which is evidence for a reasonably quick and therefore easy process of abiogenesis. On the other hand the Fermi Paradox and the apparent absence of ubiquitous alien civilisations is sometimes considered evidence for the relative rarity of life, or against the existence of ETs in general.

At the moment we have not traveled much further along the road towards proving the existence of ETs since Sagan's death; but what we have learned does not all point towards ubiquitous life in the Universe.

[Jeff Root]

Okay, two questions:

1. Do you confirm that your interpretation of "evidence for ET" is
"evidence of things we think are needed for ET to exist"?

At the moment, I see only one addition I would make to that
statement: Evidence for ET is evidence of things we think are
needed for ET to exist and things we think would make it
easier for ET to exist.

Edit to add:

Thought of something more: Any evidence of ET would also
be evidence for ET. The first is a subset of the second.

2. What do you think "but not proven" means in the title? That
we don't have proof of ET, or we don't have proof for ET?
I don't think there's any real doubt about the extrasolar planets
and so on, so why say "but not proven"?

I think that "but not proven" means "but we still don't have
unambiguous evidence of ET". We still have not proven
the existence of ET. So my interpretation of the sentence
assumes that it is grammatically disjoint. The "not proven"
refers to ET's existence rather than to evidence for ET.

-- Jeff, in Minneapolis

[Paul Beardsley]

At the moment, I see only one addition I would make to that
statement: Evidence for ET is evidence of things we think are
needed for ET to exist and things we think would make it
easier for ET to exist.

Okay, so what things are not actually needed by ET, but would make their existence easier?

I think that "but not proven" means "but we still don't have
unambiguous evidence of ET". We still have not proven
the existence of ET. So my interpretation of the sentence
assumes that it is grammatically disjoint. The "not proven"
refers to ET's existence rather than to evidence for ET.

Yeah, almost as if A.DIM had meant "evidence of ET" all along, and expected the reader to understand that.

[Swift]

To say otherwise isn't honest or scientific.

To say that we do know values for those variables
wouldn't be honest. To say that all we know about
them is that they must be greater than zero would
be just as dishonest.

OK, I want people to stop talking about "honesty" in this thread. I understand that the references may be to scientific honesty (or not), but it is too close to questioning the honesty of other members, which is too close to calling another member a liar. It is just too inflamatory. There are other ways to disagree with someone, to say they have a different opinion or interpretation, or even to say they are mistaken. Use those ways.

[Jeff Root]

Okay, so what things are not actually needed by ET,
but would make their existence easier?

Very good question, but a little outside the scope of what I
can handle at the moment. I hope others will tackle it.

Oh, I'll say one thing: Probably any "requirement" is actually
a wide range. Some part of that range would likely be more
favorable than other parts. Which is to say the requirements
are not either met or not met, but met to some degree.

I think that "but not proven" means "but we still don't have
unambiguous evidence of ET". We still have not proven
the existence of ET. So my interpretation of the sentence
assumes that it is grammatically disjoint. The "not proven"
refers to ET's existence rather than to evidence for ET.

Yeah, almost as if A.DIM had meant "evidence of ET"
all along, and expected the reader to understand that.

The title of the thread is the title of an Associated Press
article on phys.org. A.DIM linked to the article in the original
post. The short article is about the mounting evidence which
supports the expectation of the existence of ET life. Both
the scientists being interviewed and the writer of the article
clearly want to make clear that the evidence does not prove
the existence of ET life, and they explicitly say so. I have
been explaining this distinction here since December 2010.
But there is no ambiguity at all in the article. The headline
accurately, though clumsily, reflects the article's content.

-- Jeff, in Minneapolis

[Luckmeister]

But there is no ambiguity at all in the article. The headline
accurately, though clumsily, reflects the article's content.

I don't think it was clumsy. I think it was purposely misleading to attract readers, as is commonly practiced in headline writing today.

Fraser linked to an article in UT which touches on the subject of calling assumptions 'evidence' based more on wishful thinking than hard data.

[Jeff Root]

But there is no ambiguity at all in the article. The headline
accurately, though clumsily, reflects the article's content.

I don't think it was clumsy. I think it was purposely
misleading to attract readers, as is commonly practiced
in headline writing today.

How is it misleading? The first clause says what it means.
The second clause is grammatically incorrect, in seeming
to say that evidence for ET is not proven, rather than what
was meant, which is that the existence of ET is not proven.
But the meaning of the second clause is not what has been
at issue here. Everyone correctly understood the intended
meaning of the second clause.

Please explain exactly how you interpret it as misleading.
In what way does it mislead, or potentially mislead?

-- Jeff, in Minneapolis