Thanks for your response. No ridicule was ever intended by me.

Cheers,
al.

The difficulty here is in assessing the terminology and the real problems of identifying the chances of all these questions – especially among mostly novices. When there are many unknowns or uncertainties, philosophical or historical precepts are sometimes the only way to assess incomplete or complex issues with seemingly untenable answers. It might be misguided, but it surely it is at least experientially based.

As far ; "If you know differently (that these planets are sterile), then please explain how you know, because it's not based on science the general public is aware of."
I've never made the assertion either way, nor can I. However, I can be sceptical or base judgements or logical or scientific probabilities based on realistic limitations. Saying micro-organisms exist in the upper atmosphere of Venus does mean zip unless has little or no evidence to support it. Ego, until there is actual evidence to the contrary, it remains a unsubstantiated theory. Most think Mars has a better chance of finding life existing (or now extinct) than Venus – and this is based on the nature of Mars and the seemingly better conditions for biological and biochemistry to be effective to nurture or sustain organisms.. (in the case of Occum;'s razor, is this latter question more based on evidence or by its likelihood? If I have half-a-billion dollars riding on an experiment to prove life exists and have to select between Venus and Mars, for example, would I not choose Mars as the better probability of success? Yes Occum's razor might be old hat and probably some form of gambling – but it is a general scientific way via reductionism and just reflects the hope of using fewer steps to achieve ones aim. Sure it's a tool, but it is not the only tool, nor is it absolutely infallible.)

However, my own point is that we can base the origin of life on the constraint of the chemical organic compounds – especially alpha-amino acids; and the constructs of more advance structures like RNA, DNA or basic proteins.. For example,
– Most amino acids are destroyed (decomposed) between temperatures of 200C or 300C. Therefore, any created organism cannot begin or survive in regions that exceeded this value.
– All of the amino acids are soluble in water, but are insoluble in hydrocarbons or organic solvents. This means water needs to exist in liquid form for the amino acids interact with each other to disassociate and interact with polar solvent.
– Creation of catalytic enzymes to make more specialised proteins. Basic proteins have to pre-exist for the life to activate the process. etc.

In Venus' case, these conditions are presently questionable As many have alluded here, because of the hostile conditions during any known period of planetary evolution.

While transport mechanism, and the physical constraints of the environment that living cells needs to survive are important and necessary to know (and clearly fascinating), it is not the sole part of the story., Doesn't it also makes sense do chemical or biological constraints as well, and assess the real probability that the condition could induce life. From what I've read, Venus seems highly unlikely place to find either the origin of micro-organisms (spores) or the original source of earth-bound micro-organisms.

As for; " If life – the simplest form – originally took billions of years to form, then it didn't start on Earth."

Isn't this really a very broad assumption to base you whole argument upon? Where is the scientific evidence to prove or disprove that this is true?

Note: I have no real questions regarding "Do microbes survive cold, heat, desiccation, vacuum, radiation of space, etc.", as these can be scientific experimented in both space and in the laboratory.

As for Arrhenius, didn't he win a Nobel prize in chemistry? I think his work on the dissociation of organic and inorganic compounds in solutions was among his greatest works. Its funny, but the way organisms exist and thrived on Earth is based on these very principles, especially in the interactions of polar amino acids as they forming various complex molecules.

Sorry, but for me, for one of the biggest questions that mankind has ever faced (is there life off the Earth?) cannot be answered by old phosophies that contain a a "usually" in the definition. If life – the simplest form – originally took billions of years to form, then it didn't start on Earth Period. As for Venus' atmosphere and Mars having microbial life – no one knows. Period. If you know differently (that these planets are sterile), then please explain how you know, because it's not based on science the general public is aware of.

As far as my comment on the "physics", it has to do with computing the battle of force of electric field on a charged microbe (as reported in papers) vs. the force of gravity. Once you do the math and see the forces, the implications are profound.

I like to use the analogy of an island being viewed by telescope from the continental shoreline. Does one say, I wonder how life originated there? No, one wonders how life got there – usually ocean currents or air currents. I think the transfer of life between planets is similar, but with different physics, and much poorer conditions between the planets.

Then you start asking other questions. Do microbes survive cold, heat, dessication, vacuum, radiation of space, etc. The answers are yes, at least to some level.

And then you find that a nobel-prize-winner proposed the essentially same theory in 1908 (Svante Arrhenius), and, right or wrong, you're hooked for life investigating.

"Occam's razor. From wiki : "The principle (Occam's razor) states that the explanation of any phenomenon should make as few assumptions as possible. " "

This is slightly misleading, and really avoids the scientific application of reductionism. I think the better interpretation of this principle (as a positive instead of a negative connotation) is that;

"The principle of Occam's razor, is where all things being equal, the simplest explanation is usually the right (or the best)."

Note : I think Jorge earlier comment was meant; that this Venus article here seems more to advocate the theory of "norminalism" (not Occum's razor per se – Ie. Adopting a universal process that seems to have no place in the reality of proof or the reality.
I assume the conditions existing on Venus – now or in the past – are less likely to harbour life than Earth,

"Futhermore, Occum's razor is in some ways perfectly applicable – especially as we already know life exist on Earth now, and billions of years ago, and as far as we know, life doesn't seem to exist there now, nor do we have any evidence that it once did."

Should read;

"Furthermore, Occum's razor is in some ways perfectly applicable – especially as we already know life exist on Earth now, and billions of years ago, and as far as we know, life doesn't seem to exist there now on Venus (or Mars) , nor do we have any evidence that it once did."

Otherwise, it doesn't make any sense. Sorry.

I really don't understand the relationships presented here. Surely life starting anywhere is based on principles of either biology and chemistry, and is clearly not a matter of physics.
If life already exists now on Earth, and seemingly devoid on either Venus or Mars, isn't it logical that the origin of life is Earth and not Venus? As to origins of panspermia, isn't it also likely that the early beginning of life on Venus, Earth and Mars formation could have been equally seeded from either a interstellar or another interplanetary source?

The implausibility for me is that seeding of planets by some panspermia mechanism avoids the more fundamental issue of
original way these self-energising and growing simple organisms went from simple inert organic molecules by a physical process into organisms that display evidence of expiration and replication.

Futhermore, Occum's razor is in some ways perfectly applicable – especially as we already know life exist on Earth now, and billions of years ago, and as far as we know, life doesn't seem to exist there now, nor do we have any evidence that it once did.

If this is a scientific argument based on both observation and evidence, then therefore these speculations of Venus are unfounded – not because of the reality (or not) of the mechanism of transfer of biological or non-biological material between Venus and the Earth, but that no direct evidence of organisms exists anywhere else than on Earth.

As you said; "Finding microbial life on Mars, and then confirming the basic life mechanisms and DNA, would go a long way to defuse the ridicule." Until science can actually understand the way life began Unfortunately, the search by "Forearmed is forewarned" is not usually a universal scientific principle even under the observation that Occum historically is mostly correct.

General comment:
For life to form on either Earth, Venus or Mars, means the conditions for amino acids to form early organisms are by similar means or not. If, as you argue, life didn't start on Earth, then why is more probability more likely for Venus (or Mars, for example), than Earth? (Either article doesn't really say).

If say, micro-organisms could now (or once were) lie in Venus' atmosphere, but the far more difficult question is how they got there in the first place. If we assume this, isn't it therefore more realistic to say that such life formed once on the surface of the early Venus, then when the planet got to hostile (and destroyed all life and usable amino acids), the only feasible place organisms can remained is atmospheric.

I was interested in support in Tammy Polotner's article in Universe Today of 2nd April 2008 "Venus' Variable Evolution", where Prof. Fred Taylor of Oxford University is paraphrased as stating "Biological evolution could never happen", based realistically that the water once there was rapidly lost in a very short geological time scale.

Sadly, we also presently cannot test the first postulate here, but testing the Venus atmosphere could be made by article "Cruising the Cloud Tops" Universe Today article on 10th July 2008 by Nancy Atkinson. Without being cynical, this article does sounds like a drumbeat for searching for life on such a mission. I pray this isn't such motivation!

So IMO. Since we can already produce the majority of basic amino acids required for life in a simple laboratory experiment by sparking electricity into basic organic molecules to for an organic soup or goo. We must therefore show that here on Earth this same organic soup did not then turn into life (and why), before we search for alternative credible explanations for life elsewhere.

Best,
Duncan.

Good Luck Phoenix! (Finding microbial life on Mars, and then confirming the basic life mechanisms and DNA, would go a long way to defuse the ridicule).

IMO, surely the origins of life on Earth is more likely the Earth, with the less likelihood of the panspermia origins (in decending order) being the nearby planets, Mars, Venus, the Solar System, and then interstellar origins.

1) The true origins our Earth-based microbial life is significantly constrained on the creation and stability of amino acids, solely based on general chemistry and the interactions of these biochemicals in water (or some other) solutions. In the argument of life's origins beyond the Earth, I really do fail to see why these particular building blocks are any best placed, say on Venus, or Mars (or elsewhere) than the earth itself. So until the initial environmental constraints elsewhere can be proven to show that amino acids changing into life, then the Earth logically remains the most likely place for its beginnings.
As Jorge said; "Cue Occam's Razor."

2) Venus' present atmosphere is far too hostile. Even if Venus were similar to the Earth 4 billion years ago, the survival of early Venusian organisms is made worst because the planet lacks a significant magnetic field – fried to a crisp by the relentless solar radiation.

3) The transport mechanism from the Earth to Venus needs to be far better explained and proven. For example, How material interacting with the Earth's magnetic field, then survived atmosphere descent without being destroyed or even recombining. There are of course other possibilities, like the amino acids (or other organic molecules) being transported to Earth, to then form life here.

If there is microbial life in Venus's atmosphere (which I doubt), it's more likely to get blown to places like Mars. It might actually help that Mars is further from Venus than Earth is. The plume of material blown off Venus would spread out to a greater area as it moves away from the Sun and you wouldn't be so dependent on a perfect alignment between the two planets. The plume would be more sparse, but Mars would pass through it more often.