[neilep (OP)]

Dear Klevur people,


As a sheepy I of course pre-date the Earth which we all know was invented by Mr G.Aia in 1879 when he did a particularly foul poo in an ancient pond which he then dropped his phone into causing it to short out and create life.This is true because I just made it up. Got me thinking though.........



..........Some extremophile microbes can survive in near-zero energy environments for incredibly long periods by entering a state of metabolic stasis. Could there theoretically be a maximum biological timescale ? say, in the order of millions of years ? where life remains ?viable? but dormant?
And if so, does this raise the possibility that some life forms might predate Earth?s formation and have arrived here via panspermia ? essentially making some terrestrial life older than the planet itself?...Could Life Be Older Than Earth?

ewe see, i just don't know...do ewe ?

whajafink ?


sheepy Neilxxxx
















There once was a sheep quite astute,
 Who wondered if germs play the mute.
 ?Could microbes nap deep,
 For millions of sheep?
 And arrive here in cosmic commute??

[Halc]

Some extremophile microbes can survive in near-zero energy environments for incredibly long periods by entering a state of metabolic stasis. Could there theoretically be a maximum biological timescale ? say, in the order of millions of years ? where life remains ?viable? but dormant?
And if so, does this raise the possibility that some life forms might predate Earth?s formation and have arrived here via panspermia?

Not only possible, but perhaps significantly more probably than is typically assumed.

The one bit I balk at is calling it something as complex as a microbe, which seems to be pretty complex and evolved for an Earth environment.  I suspect such panspermic life forms would be truly primitive and less adapted to a specific environment.  It would probably have been embedded in some meteor quite larger than dust so the interior isn't burned up before it brings its gift to wherever it hits.

As for planets being blown to sufficient bits to throw their early life into space, yes, this happens more often than you think.  They've found Mars bits on Earth, which means not only did Mars get hit hard enough to blast some of its bits past its atmosphere and then still escape velocity, but also in sufficient quantity that enough of it made its way to Earth to get found by us.  The vast majority of meteorites are never found/studied.

[Eternal Student]

Hi,
   

The one bit I balk at is calling it something as complex as a microbe,....

   If we relax the demand for proper and completely viable lifeforms having come from somewhere else and instead just suggested that some biologically relevant molecules fell on planet earth from somewhere else, then we're really in with the most current mainstream of thinking.

      ....Analyses of three meteorites suggest that nucleobases, the crucial components of DNA, could have formed in space and then fallen to Earth to provide the raw material for the origin of life itself.....

[Taken from   "Meteorites could have brought DNA precursors to Earth",
a Natural History Museum article,  available at this URL:   
https://www.nhm.ac.uk/discover/news/2022/april/meteorites-could-have-brought-dna-precursors-earth.html ]

    Let's make it clear what is being said here:   It's not that whole, intact and viable lifeforms fell to earth,  instead it's the much weaker assumption that some very important organic compounds developed elsewhere and fell to earth.   We are not suggesting that any of these nucleobases had to be strung together in the same way as modern DNA or that any of the genetic code that may have been there if they did join together (which they would naturally tend to do) would have survived and will be present in modern day life.   We only have to go so far as to suggest that some raw materials, some nucleobases did develop elsewhere and fell to earth.

     In effect this would have given evolution a significant headstart or boost.   You should note that these organic compounds could have developed on earth and there are some sensible theories for how that may happen (or has happened)....

        The primordial soup hypothesis, suggests that intense ultraviolet radiation and lightning on the early Earth provided the energy for chemical reactions between compounds such as water, ammonia and methane to begin.
The theory suggests these reactions then led to the creation of molecules such as DNA and RNA, which subsequently became part of a self-replicating system which would ultimately become life....
   However, there are some gaps between the conditions simulated in these experiments and what we now understand about the early evolution of Earth's atmosphere.

[Extract from the same Natural History Museum article previously cited]

       The idea that some biologically relevant molecules, such as Amino acids and DNA-like material, fell to earth in meteorites is one of the most likely and reasonable ways to "shore up" the theory for the evolution of life on earth.   It is this view which now seems to be favoured over the notion of an entirely terrestrial evolution.

      It's no longer a huge leap to assume a bit more,  maybe there were/are some forms of life as suggested by @neilep that fell on planet earth and remained viable.   However, this is one of the main sections of the forum, the mainstream scientific views must take precedence and we just don't have the evidence to support this much (yet).

Best Wishes.

[alancalverd]

The interesting question, then, is not "where did life come from?" but "how did those interesting molecules form in the first place, and survive space travel in a viable form?"

[paul cotter]

It is relatively easy to imagine the abiotic formation of the purine bases: adenine is a pentamer of hydrogen cyanide and guanine is a pentamer+o. The pyrimidine bases, cytosine, thymine and uracil are not quite so easy to construct from basic molecules. Where did the sugars ribose+deoxyribose come from?, possibly formaldehyde. Even if all these precursors were present what could possibly string them all together with inorganic phosphate- one would need an enzyme to do this, so it remains a classic chicken'n'egg puzzle.

[evan_au]

Re "maximum biological timescale ... where life remains viable but dormant?"
One data point is the tardigrade, which can survive for 30 years in the dehydrated "tun" state.
- But 30 years is too short for a rock to have a high probability of traveling between planets.

A limit for complex organisms is DNA degradation due to radiation, metabolism (oxidative stress) and general chemical breakdown.
The tardigrade shows remarkable resilience, when in it's tun state of suspended animation.
- The tun state has almost no water, but a lot of preservative chemicals
- Metabolism is almost stopped, reducing oxidative stress
- It can survive about 1,000 times the radiation that would kill a human
- Cosmic rays and terrestrial radiation continues to break down DNA while it is in this state

On return to the hydrated state, the tardigrade must repair all DNA damage done while it was in suspended animation.
https://en.wikipedia.org/wiki/Tardigrade#Environmental_tolerance

[evan_au]

Another data point is the "Deep biosphere", where archaea and bacteria don't go into suspended animation, but slow their metabolism by a factor of up to a million compared to surface microbes.
- It is thought that cells may only divide every thousand years or so
- They are sustained by chemical and radiation processes in the deep rocks
- Because they have a (slow) metabolism, they are able to repair DNA damage as it occurs.
https://en.wikipedia.org/wiki/Deep_biosphere#Living_with_energy_limitation

[evan_au]

Another story: A virus that was still able to infect host after 48,000 years frozen in Siberian permafrost: Pandoravirus yedoma.
https://pmc.ncbi.nlm.nih.gov/articles/PMC10333728/