Theories on why Venus and Mars aren't inhabited by similar life forms?

Water may well have existed on Mars, there is evidence. But the atmosphere was too thin, gravity too weak, and eventually atmosphere and water boiled away.

While water is a precondition for life as we know it, the presence of water does not guarantee there is or was life, just that there could be.

In his zeal to disprove science Papa G shows his ignorance (surprise!) I studied evolutionary biology and clearly remember a professor explaining it was theoretically possible to have life forms based on silicon, rather than carbon, compounds, and ammonia rather than water as solvent. We don't know if it exists somewhere. It would not at all contradict evolution; just that evolution on such a planet would have followed a different pathway than it did on water/carbon rich Earth. Even if such oddities were found on Earth it would simply mean there have been two evolutionary pathways, not one. However, such beings would require very cold temperatures and limited oxygen, so not likely here.

Venus has a crushing CO2 atmosphere, temperature 900F, and a constant rain of sulfuric acid, as Carl Sagan said, less a goddess of beauty than a vision of hell. Venus is, in fact, an example of runaway greenhouse effect. If Mars had too little, and Earth until the past century had the right amount, Venus had/has way too much. No known life form can survive those conditions, even the "extremophiles" as they are called who live in ocean bottoms, steam vents and other inhospitable places.

The moons Europa and Titan are considered possible candidates for life; Titan at least is rich in organic compounds.

 

I'm not disproving science. What an incredibly stupid post. Thanks for making me dumber. Life as we know it doesn't have to be the only template for life in the universe, which is all I'm saying. Hell, my thoughts actually are right in line with evolution, in the life can adapt and evolve to many different environments. Disprove this ... I'll wait.

Nice personal attack, by the way. The only one who made an ignorant post is you, who again fell trap into the narrow-minded view of how life can exist.

 

There are many entries in search engines for life based on ammonia, arsenic, boron, carbon dioxide, hydrogen peroxide, nitrogen, phosphorous, polyoxometalate, or silicon. This link has been on this board before (maybe from me, I forget)

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

The reason that planetary probes search only for our system is that with no other experience, the cost of rigging sensors for unknown systems is too high. Besides, they say the probability of a planet’s life being carbon-water-oxygen based is well over 95% because--The other systems allow for very slow movement, thus slow evolution, thus low probability of being found.

 

Crandc, you'll like this. From that article:

Looking through the search engine...wow, this makes you realize why H.G. Wells was great. Only 3 years after science thinks of the silicon idea, Wells is writing about it.

http://www.daviddarling.info/encyclopedia/S/siliconlife.html

 

Dead planets really aren't that interesting. We've got the best real estate in the galaxy right here on Earth. More species of life than you can shake a stick at.

The coolest thing about space is you can see the entire Earth from there.

[video]https://www.youtube.com/watch?v=P5_GlAOCHyE[/video]