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Moontanman
Post  Post subject: Did complex life come from Mars?  |  Posted: Thu Sep 05, 2013 2:59 am
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Lately it seems to be popular to speculate that life may have originated on Mars through transfer of microbes through impact debris. Part of the mindset is that Mars cooled sooner than the Earth and may have been the source of life on Earth.

http://www.space.com/22577-earth-life-f ... heory.html

If this is true then this could explain the Cambrian "explosion", there are multicellular organisms tough enough to make the journey from Earth to Mars and by the time of the Cambrian the Earth seems to have dominated by weird organisms with no modern counterparts.

A meteor holding desiccated specimens of some tough creature, already the result of billions of years of evolution but from the same microbes that seeded early Earth, could have been thrown to Earth from Mars by an impact , some tough creature already adapted to competitive life style, the Earth fauna was wiped out and replaced by Martians!

What do you think?


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bunbury
Post  Post subject: Re: Did complex life come from Mars?  |  Posted: Thu Sep 05, 2013 3:57 am
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I think it's unlikely that an organism evolved in a specific environment could arrive at a completely new and different environment and not just survive but thrive. Most organisms cannot survive if they are transferred to a slightly different environment, let alone one that has radically different temperature, atmospheric composition, solar radiation levels, humidity, atmospheric pressure and surface characteristics. The article even mentions that Mars was dry which in their theory enabled the boron and molybdenum to catalyze the formation of RNA molecules (I think that's what they are saying) while the Earth was covered in water. Wouldn't it be a bit surprising if organisms that were created and evolved in desert conditions did just fine when they were dumped in the sea?


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marnixR
Post  Post subject: Re: Did complex life come from Mars?  |  Posted: Thu Sep 05, 2013 6:44 am
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i must i'm not clear why the occurrence of molybdenum matters in this respect - why is it thought to be essential to the origin of life ? is it because in current experiments it was required for some reactions to go ahead ?

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Moontanman
Post  Post subject: Re: Did complex life come from Mars?  |  Posted: Thu Sep 05, 2013 4:32 pm
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bunbury wrote:
I think it's unlikely that an organism evolved in a specific environment could arrive at a completely new and different environment and not just survive but thrive. Most organisms cannot survive if they are transferred to a slightly different environment, let alone one that has radically different temperature, atmospheric composition, solar radiation levels, humidity, atmospheric pressure and surface characteristics. The article even mentions that Mars was dry which in their theory enabled the boron and molybdenum to catalyze the formation of RNA molecules (I think that's what they are saying) while the Earth was covered in water. Wouldn't it be a bit surprising if organisms that were created and evolved in desert conditions did just fine when they were dumped in the sea?


Experience on Earth of introduced species would seem to negate your fist objection. Since these organisms share the same genesis as Earth life they should have no problem on Earth, Mars at the time was thought to be far more earth like than today.

The article mentions that Mars has both oceans and dry areas, not just dry.

Now to the heart of it, in fact the very Earth organisms tough enough to survive space are at least semi aquatic organisms that survive desiccation very well, Tartagrades come to mind.

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

Quote:
Physiology

Scientists have reported tardigrades in hot springs, on top of the Himalayas, under layers of solid ice and in ocean sediments. Many species can be found in a milder environment like lakes, ponds and meadows, while others can be found in stone walls and roofs. Tardigrades are most common in moist environments, but can stay active wherever they can retain at least some moisture.


Hypsibius dujardini imaged with a scanning electron microscope
Tardigrades are one of the few groups of species that are capable of reversibly suspending their metabolism and going into a state of cryptobiosis. Several species regularly survive in a dehydrated state for nearly ten years. Depending on the environment they may enter this state via anhydrobiosis, cryobiosis, osmobiosis or anoxybiosis. While in this state their metabolism lowers to less than 0.01% of normal and their water content can drop to 1% of normal. Their ability to remain desiccated for such a long period is largely dependent on the high levels of the non-reducing sugar, trehalose, which protects their membranes. In this cryptobiotic state the tardigrade is known as a tun.[23]
Tardigrades are able to survive in extreme environments that would kill almost any other animal. The following are extremes states tardigrades can survive:
Temperature – tardigrades can survive being heated for a few minutes to 151 °C (424 K or 304 F),[24] or being chilled for days at −200 °C (73 K or -328 F),[24] or some can survive temperatures for a few minutes at −273 °C (~1 degree above absolute zero/0 Kelvin or -458 F).[25]
Pressure – they can withstand the extremely low pressure of a vacuum and also very high pressures, more than 1,200 times atmospheric pressure. Tardigrades can survive the vacuum of open space and solar radiation combined for at least 10 days.[26] Some species can also withstand pressure of 6,000 atmospheres, which is nearly six times the pressure of water in the deepest ocean trench, the Mariana trench.[16]
Dehydration – although there is one report of a leg movement in a 120-year-old specimen from dried moss,[27] this is not generally considered "survival",[28] and the longest tardigrades have been shown to survive in a dry state is nearly 10 years.[29][30] When exposed to extremely low temperatures, their body composition goes from 85% water to only 3%. As water expands upon freezing, dehydration ensures the tardigrades do not get ripped apart by the freezing ice.[31]
Radiation – tardigrades can withstand 1,000 times more radiation than other animals,[32] median lethal doses of 5,000 Gy (of gamma-rays) and 6,200 Gy (of heavy ions) in hydrated animals (5 to 10 Gy could be fatal to a human).[33] The only explanation found in earlier experiments for this ability was that their lowered water state provides fewer reactants for the ionizing radiation.[34] However, subsequent research found that tardigrades, when hydrated, still remain highly resistant to shortwave UV radiation in comparison to other animals, and that one factor for this is their ability to efficiently repair damage to their DNA resulting from that exposure.[35]
Irradiation of tardigrade eggs collected directly from a natural substrate (moss) showed a clear dose-response, with a steep decline in hatchability at doses up to 4 kGy above which no eggs hatched.[36] The eggs were more tolerant to radiation late in development. No eggs irradiated at the early developmental stage hatched, and only one egg at middle stage hatched, while eggs irradiated in the late stage hatched at a rate indistinguishable from controls.[36]
Environmental toxins – there is evidence that tardigrades can undergo chemobiosis, a cryptobiotic response to high levels of environmental toxins. However, as of 2001, these laboratory results have yet to be verified.[27][28]
Outer space – tardigrades are the first known animal to survive in space. On September 2007, dehydrated tardigrades were taken into low Earth orbit on the FOTON-M3 mission carrying the BIOPAN astrobiology payload. For 10 days, groups of tardigrades were exposed to the hard vacuum of outer space, or vacuum and solar UV radiation.[37][38] After being rehydrated back on Earth, over 68% of the subjects protected from high-energy UV radiation revived within 30 minutes following rehydration, but subsequent mortality was high; many of these produced viable embryos.[26][39] In contrast, dehydrated samples exposed to the combined effect of vacuum and full solar UV radiation had significantly reduced survival, with only three subjects of Milnesium tardigradum surviving.[26] In May 2011, Italian scientists sent tardigrades into space along with other extremophiles on STS-134, the final flight of Space Shuttle Endeavour.[40][41][42] Their conclusion was that microgravity and cosmic radiation "did not significantly affect survival of tardigrades in flight, confirming that tardigrades represent a useful animal for space research."[43] In November 2011, they were among the organisms to be sent by the US-based Planetary Society on the Russian Fobos-Grunt mission's Living Interplanetary Flight Experiment to Phobos; however, the launch failed.


I think brine shrimp are another contender along with the other seasonal vernal pool shrimp that dry out sometimes for decades before coming back from resting eggs. Those eggs are very tough, last for decades buried in salt and dust waiting for rain to revive them.


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