Mars had 3/4 billion more years to develop, compared with the Earth. Mars formed first, and cooled first due to its smaller size.
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.
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.
Bear in mind that hypothesized impact is estimated to have occurred around the 4.5Gya mark. That’s still a lot further back than 3.8Gya. And I still wouldn’t categorically rule out microscopic life/life-precursors surviving the event somehow.
Geological evidence shows that the earth’s crust was molten until 3.8Gya. This corresponds with the ending of the late heavy bombardment on the moon, which Apollo samples dated. It’s hard to imagine life persisting in or around a magma ocean.
I think generally speaking people refer to life arriving and then staying as the start of life on Earth. You're probably right that it could have been and likely was spontaneously popping up and then disappearing on Earth prior to the pretty massive window as when we believe life to have "began" on Earth.
Complexity speed run to stagnation isn’t suspect at all, thats exactly what you’d expect when there is suddenly a new environment to exploit for life. Mutations are always happening. At some point a subpopulation will emerge that has a lucky few mutations that grant it an edge relative to others in fitness, then it will dominate the environment until the factors that confer success either change, or these mutants fall short of a more fit upstart mutant population. Its something you see play out even today, when an invasive species is introduced to a new environment where its traits serve it well, and quickly outcompetes native species.
Its also why we better be damn sure the mars sample return is absolutely sterile lest we contaminate our planet with extraterrestrial microbes.
Other posts answered, but only if you already know the answer. The rovers we've used on Mars have done an extremely superficial job of scouring the planet. The most recent rover Perseverance has, to my knowledge, the most capable drill with a max depth of 2.4 inches. [1] And the drill is used extremely sparingly because it tends to break quickly, as it did on Curiosity. And of course it can only drill, not excavate/cleave. The first humans on Mars will likely provide more information in a week than decades of probes and rovers have.
I am imagining an astronaut digging with a shovel and 2.5 inches below the surface are just dinosaur skeletons and stuff. Or something even more fantastical.
Exactly. There's absolutely no reason to think that advanced life did not exist on Mars except for the lack of evidence. That sounds funny, but the absence of evidence is not evidence of absence, especially in a case like this where the planet has been probably sterilized on a time frame of potentially billions of years.
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's been less than 150 miles of Mars roamed by mostly small rovers that often could barely do more than take pictures and do some basic soil chemical analysis. Do you expect to see obvious dinosaur remains with an RC car with a small shovel driving around in Kansas for 100 miles, especially if you don't even know what a dino even looks like?
I think there have been less than 100 drill holes by curiosity and perseverance the deepest being ~3” and none of those samples have returned to earth. Not sure how deep any potential fossil layers might be but that doesn’t sound like a lot.
The people who would be valuable in that role, namely highly trained scientists, mostly aren't interested in what's effectively a suicide mission. They have better options and things they're tied down to on Earth.
Look up ALH-84001. The debate about whether the structures inside this Martian meteorite are fossils is too long for a HN post. But in analyzing the rock it was shown that the during the entire trip from when it was blasted out of Mars to when it fell in Antarctica would have been survivable for rock boring microbes. Not just theoretically, but hard evidence. There are structures that would have been destroyed if the rock was heated enough to sterilize, but they survived the trip. Hundreds of tons of rock like this from Mars land every year.
No, most are smaller rocks and generally decelerate to terminal velocity in the upper atmosphere. It’s the big ones that have too much momentum and penetrate further at speed, causing them to go boom.
The underlying reason is that momentum scales with volume but air resistance scales with surface area.
While I recognize your logic, and even mostly agree, the point still stands that it cannot be conclusively and definitively said (as least as far as we've been alive/can tell) that hundreds of tons of Martian meteorites fall to Earth every year. Or even tons at all.
Tons of meteorites in general, sure — but not from Mars.
It is likely given these numbers at least some tons of Martian rock land here annually, which makes the seeding of life concept feasible. I'm on board with "not hundreds of tons", but it's a lot closer estimate than 277 ever.
(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.
There are meteorites on Earth which very likely originated from Mars. They're believed to have been launched into space by an impact, eventually finding their way onto Earth. If we're looking for the most realistic options for panspermia to have occurred, they'd be due to a natural event of this sort.
It’s very much like how islands in the sea are colonized by life. Some event causes a blob of living creatures to enter the sea on a raft and they drift until they make landfall somewhere else. Sometimes they survive long enough in the new place to reproduce.
Couldn't it just be that simple life isn't rare as long as the conditions exist for it to form. It took a very very very long time for even oxygen producing life to form after that.
I remember seeing somewhere a graph where someone plotted the "complexity" of life vs. time, I think on a log plot, and found a straight line. The line goes to (log) 0 around 5 billion years before the formation of the solar system. The inference from this admittedly dubious exercise was that life originated somewhere before our Solar system, spread here, and continued to evolve here.
Which is an important advance because genesis of life on Earth is getting harder and harder to answer as we gather more evidence. Pushing it to another environment (and longer time frame) does in fact solve a number of problems.
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.
I get your point, but the idea that life originates on Asteroids and populates planets on impact is, imo, likely. It does shift the question to “how did it start there” :)
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.
They have the chemical elements, but they do not have a source of energy that could create life.
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.
Thanks for interesting thoughts.
When reading it I get the feeling that the chances for "random" creation of complex life via Mars or directly seems almost infinitely small. To me it seems much more plausible that it was designed and created rather than a stroke of luck. Again, thanks for your thoughts.
Maybe Earth? Who knows? Lots of good sci-fi has been written about it. I recommend J.P. Hogan’s “Inherit the Stars”, which starts with evidence of human spaceflight predating known history and goes on interesting directions.
