Actually it's quite likely that life did develop on Mars, and may still be there. And in the early solar system - was as good a place to live, for life, as Earth.
So life on the planet Mars would probably be just as it is now. I.e. might be a few microbes. Maybe lichens. But intelligent Martians and higher animals unlikely - just isn't enough oxygen there for them to sustain such a high metabolism. If there ever were creatures like that on Mars - then they became extinct probably billions of years ago, not just millions of years ago.
This has been known since the 1920s when they could already do reasonably precise determination of the composition of the Mars atmosphere - and even back then knew that it is mainly CO2 gas.
There is also a chance of underground habitats not connected to the surface. On Earth then habitats like that can have some multi-cellular life -so worms a few mms long, that sort of thing. And there could be lichens covering parts of Mars surface. But - that seems likely to be it, for present day Mars.
We haven't discovered it yet, but there is increasing evidence suggesting habitats for microbes all over the surface of Mars.
Particularly see this video
Recent very up beat results suggesting possibility of drops of liquid water over much of Mars. See also Martian salts must touch ice to make liquid water, study shows
As he says for higher animals - these are tiny insignificant damp patches of no use at all - but for a bacteria, a tiny drop of water is like a huge swimming pool.
So there could easily be microbial life on Mars right now, all over its surface except perhaps in the very dry equatorial regions - and even there - you have the warm seasonal flows - not well understood but only possible explanation found so far is liquid water - you get those in equatorial regions so may be liquid water there also in small patches here and there.
Water evaporates very quickly on Mars. But put it next to a lump of salt, as ice, and it can form a habitat for a few hours a day.
Cosmic radiation is not an issue for microbes on Mars. Levels on the surface are comparable to those inside of the ISS which actually has a problem with containing microbes. And after all many radioresistant microbes can withstand levels of radiation that would kill humans very quickly. So just the fact that they are contemplating sending humans to Mars or indeed interplanetary spaceflight (there is more radiation in free space than on the surface of Mars) shows that microbes can withstand those conditions.
It's true that this is a major issue for dormant life on Mars - if dormant for say 100,000 years, not much chance of recovery (while on Earth life has been revived after dormancy for millions of years).
However - the surface life in these habitats would revive every year. And radioresistant microbes can repair damage to their DNA while still alive and metabolizing - they have special donut shaped structures that hold the DNA fragments together after the cosmic rays slices them up - and given a few hours to metabolize - can, remarkably just put all the DNA back together again. They could repair equivalent of decades of Mars surface radiation - and just continue growing.
Here for instance, 2.5 kGy of damage is repaired within 3 hours in metabolizing Chroococcidiopsis. (That's a green algae which for many reasons is one of the best candidates for an Earth microbe likely to be able to survive on present day Mars, so may be a possible analog for Martian microbes).
Curiosity measured 76 mGy per year at the surface - so 2.5 kGy corresponds to 2500/76 or 32 years of radiation so if it wakes up for an average of 3 hours every 32 years - not much given that these habitats seem likely to make parts of Mars habitable for a few hours for many days every year - that would be enough to keep it free of damage from cosmic radiation indefinitely.
I mention that because it seems that quite a few people still believe that ionizing radiation is a limiting factor for life on Mars.
And there are many articles you can find on-line published prior to 2008 that say just this, so easy to get the impression that scientists still think that way.
But - we no longer think that way - used to be - pre 2008 then most scientists thought that present day life on the surface of Mars is impossible because the only way it could exist is in dormant form right now.
Nowadays the range of views goes from marginally possible to quite likely, and there was a big conference last year about it, on the The Present-Day Habitability of Mars 2013
I haven't seen any published articles in recent times, later than say 2008, saying it is totally impossible.
There are some people think this work on possible habitats on Mars is still speculative and who are not convinced by it yet. They would need more evidence to be convinced that these habitats actually do exist on Mars - which is fair enough - is one thing to do an experiment with your best simulations on Earth - is another thing to actually look for those habitats on Mars itself.
But if the habitats do exist, wet, and also nutritious, nobody in any of the published papers I've seen questions that microbes could thrive there.
It is of course, a factor that makes the habitats somewhat less habitable - i.e. of course microbes there would need to be reasonably radiation resistant, to survive long term, so that can rule out some possible lifeforms.
They thought that Mars was only briefly habitable on the surface every few million years or tens of millions of years. So, dormant life would soon be destroyed on geological timescales - might survive underground - and emerge to the surface from time to time. But if so, so they used to think, it would be long gone by now.
But since 2008, increasing evidence now for these present day liquid water habitats on Mars - meaning that life could be there continuously.
Now you get scientists often giving up beat remarks about potential for finding present day life on Mars - as in this video.
Now - Mars is basically in a snowball phase. It's lost all its water as well though, nearly all - which is why it is red rather than white.
Earth went through similar phases in the past when it was covered in ice, and only a few microbes survived. It had a few multi-cellular lifeforms just before the most recent snowball phase. But most developed after it.
But - judging by the similar habitats on Earth today - such as the Atacama desert and McMurdo dry valleys in Antarctica - then - if Earth did go into another snowball phase (not likely to happen now, this close to the sun) - then everything would go extinct except microbes. Possibly some lichens or some such but might well be that there is nothing left except microbes because it is just too cold and dry for anything else. On the surface anyway. And - from a distance it would seem totally lifeless. Because what life there is would be just beneath the surface of rocks and the soil most of it. Might be occasional dark patches here and there - but you would be hard put to identify any organics in them from orbit.
So - that sounds quite a bit like Mars.
If you were to move Earth out to Mars orbit, and leave it for a few billion years - you'd end up with something very similar to Mars.
Especially if you also reduce its gravity to 40%, remove its ionosphere - then without the magnetic field it would probably lose all its water as well like Mars. And nothing left except microbes.
So - that's what would happen to life on Mars.
In the early solar system however it was far more habitable. It had hot oceans - indeed very early on believed it had water at pressure cooker type temperatures - with extremely dense atmosphere as well, similar to Venus - Earth, Mars and Venus probably all started off with very similar atmosphere and oceans.
There is no longer much question about this, the evidence for early oceans is overwhelming. There is some question about whether they were ice covered - and how soon they froze over. But is also clear that originally in the very early solar system, they were not only clear of ice, but also boiling hot oceans that gradually cooled down.
As it gradually cooled down - then -it might well have entered a habitable phase before the Earth. And for some millions, and quite possibly tens or hundreds of millions of years - might well have been one of the most pleasant places in the solar system to be if you are DNA based organic life.
As to what kind of life that was, nobody knows yet. Could conceivably even have developed to multi-cellular life either then or in the later period of repeated small scale floods. Or things like stromatolites - bacterial colonies.
But if it did - then - by now it is probably all extinct. Except for some microbes, and for maybe some lichens and such like.
And the interesting thing about those, if they exist, is that they may well have evolved independently of Earth for billions of years. Even if there has been some exchange of space hardy microbes (most microbes are not space hardy) - in centuries long trips on asteroid impact debris through the vacuum and cosmic radiation of space - still - it is likely that most life on Mars would be only distantly related to Earth life and might have a different biochemistry, different metabolism, different ways of doing photosynthesis or whatever.
In most exciting case might even have totally different biology maybe based on XNA or even not on a DNA spiral type structure at all but something else we haven't thought of.
So life on the planet Mars would probably be just as it is now. I.e. might be a few microbes. Maybe lichens. But intelligent Martians and higher animals unlikely - just isn't enough oxygen there for them to sustain such a high metabolism. If there ever were creatures like that on Mars - then they became extinct probably billions of years ago, not just millions of years ago.
This has been known since the 1920s when they could already do reasonably precise determination of the composition of the Mars atmosphere - and even back then knew that it is mainly CO2 gas.
There is also a chance of underground habitats not connected to the surface. On Earth then habitats like that can have some multi-cellular life -so worms a few mms long, that sort of thing. And there could be lichens covering parts of Mars surface. But - that seems likely to be it, for present day Mars.
HABITATS FOR MICROBES ON MARS
We haven't discovered it yet, but there is increasing evidence suggesting habitats for microbes all over the surface of Mars.
Particularly see this video
Recent very up beat results suggesting possibility of drops of liquid water over much of Mars. See also Martian salts must touch ice to make liquid water, study shows
As he says for higher animals - these are tiny insignificant damp patches of no use at all - but for a bacteria, a tiny drop of water is like a huge swimming pool.
So there could easily be microbial life on Mars right now, all over its surface except perhaps in the very dry equatorial regions - and even there - you have the warm seasonal flows - not well understood but only possible explanation found so far is liquid water - you get those in equatorial regions so may be liquid water there also in small patches here and there.
Water evaporates very quickly on Mars. But put it next to a lump of salt, as ice, and it can form a habitat for a few hours a day.
WHY COSMIC RADIATION DOESN'T MATTER
Cosmic radiation is not an issue for microbes on Mars. Levels on the surface are comparable to those inside of the ISS which actually has a problem with containing microbes. And after all many radioresistant microbes can withstand levels of radiation that would kill humans very quickly. So just the fact that they are contemplating sending humans to Mars or indeed interplanetary spaceflight (there is more radiation in free space than on the surface of Mars) shows that microbes can withstand those conditions.
It's true that this is a major issue for dormant life on Mars - if dormant for say 100,000 years, not much chance of recovery (while on Earth life has been revived after dormancy for millions of years).
However - the surface life in these habitats would revive every year. And radioresistant microbes can repair damage to their DNA while still alive and metabolizing - they have special donut shaped structures that hold the DNA fragments together after the cosmic rays slices them up - and given a few hours to metabolize - can, remarkably just put all the DNA back together again. They could repair equivalent of decades of Mars surface radiation - and just continue growing.
Here for instance, 2.5 kGy of damage is repaired within 3 hours in metabolizing Chroococcidiopsis. (That's a green algae which for many reasons is one of the best candidates for an Earth microbe likely to be able to survive on present day Mars, so may be a possible analog for Martian microbes).
Curiosity measured 76 mGy per year at the surface - so 2.5 kGy corresponds to 2500/76 or 32 years of radiation so if it wakes up for an average of 3 hours every 32 years - not much given that these habitats seem likely to make parts of Mars habitable for a few hours for many days every year - that would be enough to keep it free of damage from cosmic radiation indefinitely.
MANY SEEM TO THINK THAT IONIZING RADIATION WOULD STERILIZE PRESENT DAY MARS SURFACE
I mention that because it seems that quite a few people still believe that ionizing radiation is a limiting factor for life on Mars.
And there are many articles you can find on-line published prior to 2008 that say just this, so easy to get the impression that scientists still think that way.
But - we no longer think that way - used to be - pre 2008 then most scientists thought that present day life on the surface of Mars is impossible because the only way it could exist is in dormant form right now.
Nowadays the range of views goes from marginally possible to quite likely, and there was a big conference last year about it, on the The Present-Day Habitability of Mars 2013
I haven't seen any published articles in recent times, later than say 2008, saying it is totally impossible.
There are some people think this work on possible habitats on Mars is still speculative and who are not convinced by it yet. They would need more evidence to be convinced that these habitats actually do exist on Mars - which is fair enough - is one thing to do an experiment with your best simulations on Earth - is another thing to actually look for those habitats on Mars itself.
But if the habitats do exist, wet, and also nutritious, nobody in any of the published papers I've seen questions that microbes could thrive there.
It is of course, a factor that makes the habitats somewhat less habitable - i.e. of course microbes there would need to be reasonably radiation resistant, to survive long term, so that can rule out some possible lifeforms.
WHY MANY USED TO THINK IT WAS IMPOSSIBLE PRE 2008
They thought that Mars was only briefly habitable on the surface every few million years or tens of millions of years. So, dormant life would soon be destroyed on geological timescales - might survive underground - and emerge to the surface from time to time. But if so, so they used to think, it would be long gone by now.
But since 2008, increasing evidence now for these present day liquid water habitats on Mars - meaning that life could be there continuously.
Now you get scientists often giving up beat remarks about potential for finding present day life on Mars - as in this video.
PRESENT DAY MARS IS LIKE EARTH WHEN IT WAS IN A SNOWBALL PHASE
Now - Mars is basically in a snowball phase. It's lost all its water as well though, nearly all - which is why it is red rather than white.
Earth went through similar phases in the past when it was covered in ice, and only a few microbes survived. It had a few multi-cellular lifeforms just before the most recent snowball phase. But most developed after it.
But - judging by the similar habitats on Earth today - such as the Atacama desert and McMurdo dry valleys in Antarctica - then - if Earth did go into another snowball phase (not likely to happen now, this close to the sun) - then everything would go extinct except microbes. Possibly some lichens or some such but might well be that there is nothing left except microbes because it is just too cold and dry for anything else. On the surface anyway. And - from a distance it would seem totally lifeless. Because what life there is would be just beneath the surface of rocks and the soil most of it. Might be occasional dark patches here and there - but you would be hard put to identify any organics in them from orbit.
So - that sounds quite a bit like Mars.
MOVE EARTH TO MARS ORBIT, AND IT WOULD TURN INTO A NEAR CLONE OF MARS
If you were to move Earth out to Mars orbit, and leave it for a few billion years - you'd end up with something very similar to Mars.
Especially if you also reduce its gravity to 40%, remove its ionosphere - then without the magnetic field it would probably lose all its water as well like Mars. And nothing left except microbes.
So - that's what would happen to life on Mars.
MARS ORIGINALLY HABITABLE
In the early solar system however it was far more habitable. It had hot oceans - indeed very early on believed it had water at pressure cooker type temperatures - with extremely dense atmosphere as well, similar to Venus - Earth, Mars and Venus probably all started off with very similar atmosphere and oceans.
There is no longer much question about this, the evidence for early oceans is overwhelming. There is some question about whether they were ice covered - and how soon they froze over. But is also clear that originally in the very early solar system, they were not only clear of ice, but also boiling hot oceans that gradually cooled down.
As it gradually cooled down - then -it might well have entered a habitable phase before the Earth. And for some millions, and quite possibly tens or hundreds of millions of years - might well have been one of the most pleasant places in the solar system to be if you are DNA based organic life.
As to what kind of life that was, nobody knows yet. Could conceivably even have developed to multi-cellular life either then or in the later period of repeated small scale floods. Or things like stromatolites - bacterial colonies.
But if it did - then - by now it is probably all extinct. Except for some microbes, and for maybe some lichens and such like.
INTEREST IN THIS PRESENT DAY LIFE ON MARS
And the interesting thing about those, if they exist, is that they may well have evolved independently of Earth for billions of years. Even if there has been some exchange of space hardy microbes (most microbes are not space hardy) - in centuries long trips on asteroid impact debris through the vacuum and cosmic radiation of space - still - it is likely that most life on Mars would be only distantly related to Earth life and might have a different biochemistry, different metabolism, different ways of doing photosynthesis or whatever.
In most exciting case might even have totally different biology maybe based on XNA or even not on a DNA spiral type structure at all but something else we haven't thought of.
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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