Maybe we are about to discover that we came to Earth after messing up Mars.
To be clear, Mars’ descent into inhospitality was totally natural and the result of a smaller planet with stripped atmosphere just outside the habitable zone as the Sun cooled. I doubt Martian life developed to be multicellular. But I bet when we go we’ll find fossils of algae colonies and cyanobacteria, and maybe even some living remnants underground.
The only thing panspermia can tell us is that it's ok if we can't find evidence for the genesis of life on Earth.
However, haven't we roughly recreated the process in a lab in the last couple of decades?
And we may never have the answer because we simply can't know because no one was there because nothing was there. But there's a plausible enough explanation that we don't need to invoke the extraterrestrial and all of its problems.
And I think that's part of the appeal of panspermia, it makes life extraterrestrial. And if it is extraterrestrial in origin, then it could have happened elsewhere. Whereas if the genesis of life is contained to Earth, then the chances go down that it happened somewhere else.
But they don't have nearly as many opportunities to react as in a hot planet with an atmosphere. So pushing that life started there instead of only recognizing it's a very unlikely (but still possible) possibility isn't sustained by evidence.
For the appearance of life, a planet with a hot interior and volcanism is necessary, so that minerals that are stable only at high temperatures in the interior are ejected to the surface, where after cooling down they are no longer in chemical equilibrium, providing the energy necessary to drive the synthesis of organic macromolecules (by producing through chemical reactions with water reduced compounds like dihydrogen and carbon monoxide, which can reduce the abundant carbon dioxide and dinitrogen to eventually generate amino-acids).
The solar energy cannot play any role in the appearance of life, because harvesting it requires systems that are much more complex than those that appear naturally in the inorganic minerals and fluids.
While the Earth had certainly all the preconditions for the appearance of life right here, it is likely that Mars also had them in the beginning.
What another poster has said is plausible, i.e. the only reason for supposing that life could have been brought on Earth from another place is that life has appeared rather quickly on Earth, even if this is an event with a much lower probability than all the other events that have occurred after that during the evolution towards more complex forms of life, which have required billions of years to happen.
If life has been transferred to Earth from elsewhere, Mars is the only plausible source, because it had the conditions necessary to generate life long enough before Earth and because fragments from Mars have been frequently transported to Earth, where they fall as meteorites, after being ejected from Mars by impacts that happened there, which is easier than from other planets due to the lower gravity.
Despite the fact that it is not impossible, I doubt that life has been brought from Mars, but it is indeed puzzling that life seems to have appeared very quickly on Earth.
There are also facts that are hard to explain by the hypothesis of transfer from Mars. If that happened, than the forms of life that have been transferred must have consisted of at least one kind of autotrophic "bacteria" and at least several distinct kinds of viruses, to explain all the existing living beings as their descendants.
There is considerable evidence for the fact that the current genetic code of the nucleic acids is the product of a long evolution process. In the beginning there must have been a simpler code where many more combinations were equivalent and which encoded no more than 10 amino-acids, perhaps only 6 or even only 4 in its original variant. So very ancient "bacteria" may have superficially looked like modern bacteria but they must have had a quite different metabolism. In the hypothesis where life has moved between planets, there would be an open problem of when had the transfer happened during this early evolution of the genetic system.
On Earth there has remained no survivor with a much simpler genetic code (though there are a few examples of only slightly simpler genetic codes than the canonic variant). Perhaps the earlier living beings were completely uncompetitive with the modern ones, so they have been eaten or they have starved to death. In the case of a transfer from Mars, it would also exist the possibility that only living beings with a complex genetic code had survived through a transfer and the others had remained on Mars.
One of the outstanding problems in astrobiology I mention is that the Earth was inhospitable until 3.8Gya, and the oldest fossils of presumably DNA based life (since it matches existing life we can study) was 3.7Gya. Mars was hospitable ~4.5Gya. So either life emerged IMMEDIATELY on Earth and did a complexity speed run before slowing down and remaining stagnant for the next billion years or so, or it emerged on Mars first and Earth was seeded once it was cool enough.
277 total Martian meteorites — with the largest weighing 14.5 kg — is not hundreds of tons yearly.
That's obviously not the actual total that have ever made it here.
https://science.nasa.gov/solar-system/meteors-meteorites/fac...
> Scientists estimate that about 48.5 tons (44,000 kilograms) of meteoritic material falls on Earth each day.
That has been going on for billions of years. If the 277/72,000 proportion holds that's a lot of material.
Tons of meteorites in general, sure — but not from Mars.
(48.5 * 365) * (277 / 72,000) = 68 tons per year as an extremely speculative estimate here, ignoring entirely probable variances in what hits us (much of which is sand-grain sized) versus what we identify... and again, any estimate here we have to multiply by a few billion years.
Most of it gets destroyed on entry, right? No organic matter surviving?
The underlying reason is that momentum scales with volume but air resistance scales with surface area.
And it wouldn't be technologically hard to do it such that no trace remains over those timescales.
So, yes, that's "crazy". On the other hand, it's unfalsifiable in the absence of other theories.
I'm just saying unfalsifiability is a bitch, and it's hard to find hard evidence on geologic timescales.
Besides, deciding what was inhospitable for early life is an exercise of noisy assumptions. I'd bet the error margin is larger than that difference.
800 million is greater than 3/4 billion?
At the very least, I would expect something akin to chalk left behind by proto-diatoms that had calcium carbonate skeletons.
Things kids can think up, that we can most certainly do that would put us insanely ahead but ... we just don't?
Like, why do we visit the moon but not have people stay there at all? Why are there no structures there?
Why do we ignore the Earth's mysteries a lot and go directly to Mars?
I mean maybe its a lot compared to 20 years ago but in absolute terms? It’s practically nothing, isnt it?
[1] - https://attheu.utah.edu/facultystaff/qa-perseverance-rovers-...
The Great Pyramid of Giza is a massive and extremely hardy structure that will outlast all modern buildings. Yet it's substantially deteriorating after less than 5,000 years, and it will eventually just completely disintegrate, absent the already ongoing preservation/restoration efforts. It might take 20,000 years, maybe a million. A quick search on the internet suggests nobody really knows, other than that it will happen. And now we're talking about time frames of billions of years. So what would a sterilized, perpetually radiated, atmosphere free Earth over billions of years look like, paired with never-ending massive dust storms (as on Mars)? Well, probably not especially unlike Mars does today. But oh what treasures would await you far below the surface!
I don't necessarily think anything does await us, but who knows? It's a tantalizing possibility that we won't be able to dismiss until we have humans on Mars. It's vaguely analogous to the early observations of 'canals' on Mars [1] whose explanation ranged from running water to active geoengineering from another advanced species on the planet. Their exact meaning was debated all the way into the mid 20th century, until we finally were able to get probes that could take 'high res' photos of the surface that showed they were definitely just optical illusions. A disappointing discovery, but nonetheless emphasizing that the importance of actually testing things instead of just relying on indirect instrumentation/data of this era or that.
Though they discuss how advanced civilizations could have existed on Earth and we might not even know it because there wouldn’t be much left and what was left might be so unusual that we might chalk it up to natural phenomena.
There is much uncertainty about this. The early Earth was a volatile place with a lot of raw materials and energy available, and a lot of chemistry happening. I wouldn't rule out that some part of Earth may have had the right conditions for life right from the beginning. Certainly if we expect life to be able to survive a ride on a piece of ejecta from Mars, it's plausible to imagine it surviving in some boundary niche amidst the heat and fury of the Hadean Earth.
Even if it was, it wouldn't have survived the impact that created the Moon.
Its also why we better be damn sure the mars sample return is absolutely sterile lest we contaminate our planet with extraterrestrial microbes.
I think it was maybe from this source? https://www.sciencedirect.com/science/article/abs/pii/B97801...
[1] - https://www.space.com/mars-meteorites-on-earth-mystery
[2] - https://en.wikipedia.org/wiki/Tardigrade#Survival_after_expo...
Is that enough energy to boil the living things that might be in the rock?
Huh?
The Sun has consistently gotten hotter with age.
Mars was somewhat warmer before, but that was not because of geothermal, but because it used to have a thicker atmosphere, and that retained heat better.
https://en.m.wikipedia.org/wiki/Geologic_temperature_record#...
Sun becomes hotter with time passed, not cooler.
> Early panspermia from Mars settles a LOT of astrobiological questions about origin of life and LUCA complexity.
Does it solves questons or just moves them to another planet?
OK I know it sounds crazy...but it's fun to link legends with science.
Your point still stands.
I, for one, am not planning to leave earth anytime soon, thanks.
https://en.wikipedia.org/wiki/Tom_Van_Flandern#Exploding_pla...