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If somehow Mars suddenly had our exact atmosphere, could there be lots of life in a few million years? Would the temperature rise quickly? Would the ice caps melt? Could the life be as advanced as modern humans?

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    $\begingroup$ Our terran atmosphere contains lots of bacteria, fungus spores, plant seeds, and living things in general. The lowest temperatures on earth are quite lower than the warmest temperatures on mars, so if you move our exact atmosphere to mars, some of these organisms would start to thrive quickly. Also, humans would start colonizing mars in a few dozen years if it had a breathable atmosphere. So yes, there would be life, even as advanced as humans, in much less than a few million years. But i guess that wasn't your question. $\endgroup$ – Guntram Blohm supports Monica Dec 13 '14 at 23:08
  • $\begingroup$ Keep in mind we're still not 100% certain what started life here on Earth, nor do we have a precise idea of how likely/unlikely it was given the conditions when it actually happened. $\endgroup$ – GrandOpener Jan 5 '16 at 23:20
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Atmosphere is not enough - it would also need water.

And Mars already had both atmosphere and water: Mars would lose both new atmosphere and new water for exactly same reasons it did lost them before, in a similar timeframe (around a billion years or so) or even sooner (because now its core is less active, creating weaker magnetic protection). So if any primitive life evolved (and it would be harder on Mars, because its dead crust is much thicker and the planet is geologically almost dead) any new life would die out soon as water and atmosphere are stripped by solar wind.

So the answer is: No. Life would take many millions of years to evolve, and conditions would revert to the existing conditions pretty soon (in a geological sense).

Also as @jamesqf correctly noted, when life emerged on Earth, atmosphere was very different from present one, with no oxygen.

It is not obvious if life can emerge in any atmosphere with free oxygen like the terran one, because oxygen was poison for first primitive life, and current terran life still needs to protect its molecules from oxidation damage (by handling oxygen very carefully).

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  • $\begingroup$ I am wondering if the lack of magnetic field could be solved using technology. Put a superconducting cable all the way around the equator. Pump some current into it while it is cooling down. As long as it is cold enough, that current will just keep flowing. I have no idea whether such a planet-scale electromagnet would be strong enough to protect a planet from the solar wind. $\endgroup$ – kasperd Dec 14 '14 at 20:36
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    $\begingroup$ It wouldn't necessarily have to do any work. If the force is perpendicular to the motion, no work is done. The direction of the particle would be changed, but it would still have the same amount of energy. $\endgroup$ – kasperd Dec 14 '14 at 20:56
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    $\begingroup$ @kasperd ...what? Your comment shows a fundamental lack of understanding of what energy, work, and forces are. Energy is imparted via Work, Work = Force x Distance, Force = Mass x Acceleration, Acceleration = Delta (change) in Velocity, Velocity = Delta Speed x Delta Direction. A change in direction is a change in energy, as it is a change in Direction which is a change in Velocity which is an Acceleration which requires a Force, which is a form of Work, which imparts Energy. Your idea violates the laws of physics. $\endgroup$ – Alice Dec 15 '14 at 3:36
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    $\begingroup$ @Alice a change in velocity isn't necessarily a change in energy. Or where does the energy come from to constantly change the moon's velocity so that it stays in orbit around the earth instead of heading off in a straight line? $\endgroup$ – hobbs Dec 15 '14 at 6:31
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    $\begingroup$ @Alice work is the dot product of vectors. A force on an object that acts perpendicular to the object's motion does no work. $\endgroup$ – hobbs Dec 15 '14 at 6:34
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If you're asking whether life could arise on a Mars that suddenly became Earthlike, you have to remember that Earth life did not arise on an Earth that was at all like our present conditions. The atmosphere was probably mostly methane (though there are other theories), with little free oxygen. See e.g. the "Great Oxidation Event".

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  • $\begingroup$ Good point. Even if our atmosphere was wrapped around Mars, without life to maintain its oxygen content it wouldn't stay an Earth-like atmosphere for long. $\endgroup$ – trichoplax Dec 14 '14 at 18:22
  • $\begingroup$ Excellent note. Defending DNA/RNA from oxidation damage would be yet another task which new life need to handle. It is quite possible that life cannot even emerge in atmosphere with oxygen, and develops ways to deal with oxygen only later, when faster oxygen-based metabolism is competitive advantage. $\endgroup$ – Peter M. - stands for Monica Dec 14 '14 at 19:12
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Short answer: No.

Long answer: We have two scenarios to consider. Four billion years ago Mars had Earth-like conditions and water in its liquid form, but we are still unsure if there was life, even in the form of bacteria. And even if it was, it is highly unlikely that it survived the last four billon years of very harsh conditions. So, scenario one, given that only the Mars' atmosphere changes to match Earth, but there is no life on Mars at all, a few million years won't change anything. You would probably need another billion for life to emerge via abiogenesis or for a viable "panspermia accident" to occur (ie. a meteor containing bacterias or other form of microbiological life hitting the surface in a way that doesn't destroy them and in a place which makes it possible for them to survive and develop).

Also note that even if you want Martian polar ice caps to melt, you would need atmosphere which would produce a massive greenhouse effect - denser and more richh in CO2 than Earth's atmosphere.

But, scenario two, let's say some extremophilic strains of microorganisms survived those billions of years or - more probable - our spacecrafts carried some on them. If the atmosphere changed suddenly to match ours, such microorganisms could reproduce and in a few million years they might evolve in ways very different from their Terran ancestors. Still, it would be just extremophilic microorganisms, living on a cold, desert planet.

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I would point out, for arguments sake that:

  • We do not know how life started on Earth.
  • We do not know that there is no life on Mars.

As such, not only could it be conceivable that within a few million years with an Earth atmosphere life could originate on Mars, it's also entirely conceivable that it'd never happen or that it's already happening with Mars's existing atmosphere.

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  • $\begingroup$ pfft. Both points are irrelevant. $\endgroup$ – Carl Witthoft Dec 14 '14 at 16:28
  • $\begingroup$ We do know how life started on Earth. No, not exactly in the sense that we can point to a single process in a single moment in time and state "Ah, this is how and where and when life started", but we know of a number of processes which collectively lowered the energy barrier to forming self catalyzing systems, and we know a general timeframe of when this occurred. Furthermore, he specifies in the question "lots of life", not "small amounts of bacteria thriving in puddles on the poles". Finally, how in the world does any of that mean it is conceivable it would never happen? $\endgroup$ – Alice Dec 15 '14 at 3:39
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    $\begingroup$ @Alice I'd suggest that what you think you know, and what you know are greatly different. There may be some theories, heck even good sounding ones with lots of evidence, on how life formed, but to say in any authoritative manner 'we know' is laughable. $\endgroup$ – NPSF3000 Dec 15 '14 at 6:22
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    $\begingroup$ We think we know how life formed. We'll never know for sure where it formed. $\endgroup$ – Moriarty Dec 15 '14 at 10:54
  • $\begingroup$ @Moriarty I can agree with the former (certainly, some people may think that they have a/the solution for how life formed) though I'd clarify the second - you think that we'll never know where it formed. $\endgroup$ – NPSF3000 Dec 15 '14 at 11:01
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One of the biggest problems is gravity. Mars's gravity is not strong enough to not leak oxygen. So even if you had an earth like atmosphere and water, it might not stay that way for long.

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  • $\begingroup$ It isn't gravity that is the problem, it's the lack of a magnetic field to protect the atmosphere (though the smaller gravity doesn't help). $\endgroup$ – Alice Dec 15 '14 at 3:39
  • $\begingroup$ @Alice I think you're right that the lack of a magnetic field is the dominant cause of atmosphere loss on Mars. But perhaps even if there were a sufficiently protective magnetic field, the thermal loss of a warmer and thicker Martian atmosphere would be substantial? I'm sure a few back-of-the-envelope calculations could make an interesting answer to the original question... $\endgroup$ – Moriarty Dec 15 '14 at 10:52
  • $\begingroup$ Leakage is only a problem on long timescales - many millions of years. So if you are e.g. terraforming Mars by delivering volatiles from comets or Jovian moons, once you've established the atmosphere, you'd just need to deliver a comparatively small to sustain an Earthlike atmospheric pressure. $\endgroup$ – jamesqf Dec 16 '14 at 18:02

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