Something worth noting in a lot of these discussions about extraterrestrial organic chemistry is that, assuming that things like electron orbitals and atomic charge work the same across the observable universe, we'd expect to see a lot of the same organic molecules form in similar ways. Life is carbon-based because carbon is the lightest atom that allows for long-chain molecules; oxygen is going to be widely present because its electronegativity allows for a range of interesting interactions; and broadly a number of things like amino acids should be expected to form in similar ways because of the atomic interactions that lead to them. I don't know if we've got a similar theory for why organic molecules on earth exhibit the same chirality except path dependence, but it's possible there's an atomic reason the L-type became dominant here, too. An awful lot of this stuff isn't "a roll of the dice", but an outcome of the physics of atomic and molecular interactions, and we'd expect to see similar elsewhere given the presence of both the atomic constituents and excess energy in the environment.
Is there a larger point to this? I'm not an expert, but it seems like this could point to 2 things:
1. The Urey-Miller experiment was a side show: amino acids could be delivered to a young earth via meteor. That could Kickstart abiogenesis. A more distant possibility is that abiogenesis occurred somewhere other than on earth.
2. This is soft evidence of extraterrestrial life.
It's just evidence that keeps the possibility of panspermia open.
In the years since the Urey-Miller experiment, all of the bases in DNA/RNA have been shown to form in a huge variety of conditions, many of which would have been present before the oceans even fully condensed so its not considered a goldilocks problem anymore. On top of that, it looks more and more likely that some sort of extremophile archae that would have evolved in those extreme conditions are the common ancestors of life instead of a branch that evolved separately.
Panspermia is possible but there's plenty of evidence that life emerged on earth without external help.
I would say that this makes panspermia less likely as it suggests that the components for life emerge everywhere so they aren’t that rare to require a transportation mechanism.
That's like the intelligent design argument. If life couldn't form on Earth without external help, how did it form anywhere else without external help? It makes no sense.
Turns out we do have an idea: Amino acids, nucleotides, and lipids have all been experimentally shown to spontaneously form and assemble in extreme environments. They were forming and bubbling around before the oceans even stopped boiling. After hundreds of millions if not billions of years of bumping around, they finally assembled into something that could self replicate an encapsulated cell and life took off.
It's a lot more plausible the same way that general relativity is more plausible than Ptolemiac astrophysics.
Before people jump to conclusions panspermia really only matters if a) life and its components is extremely rare and/or b) the creation of the precursors for life has to happen in space.
There is strong evidence to suggest that life have started on earth multiple times, it’s nice we find amino acids and other complex compounds on small rocks in space but it would only matter if these compounds somehow don’t form on much bigger rocks like planets.
So the evidence we collected from asteroids and comments so far mainly suggests that the components needed for life can and do form pretty much anywhere at least in our solar system.
One really fascinating thing is that the earliest known life we have on Earth is unexpectedly complex in terms of its DNA. If one looks at how the complexity evolved to modern day, and then ectrapolates backwards, it looks like the DNA would have been pretty simple around the time when the universe was still reasonably warm. So, it could have happened that very simple lifeforms formed on somewhere in the early universe and arrived on Earth on asteroids.
Kurtzgesagt did a nice video on thus recently. I always thought panspermia was totally ridiculous theory, but there are some nice arguments behind it.
Just so we're all clear, no one has any idea how life could have emerged on Earth without external help.
It's a long way from amino acids to life -- like the distance between the squiggles that make up the letters of the alphabet and Milton's Paradise Lost.
I mean, why not just declare Carbon, Hydrogen, and Oxygen to be "precursors for life" and then declare "the ingredients were already there!"
For those who are genuinely interested, check out the book The Stairway to Life: An Origin-of-Life Reality Check by Tan & Stadler.
There's quite a number of different theories for how life could've emerged on Earth.
Currently most popular, as I understand it, is the hydrothermal vent hypothesis, which uses the energy gradient provided by the heat from underwater hydrothermal vents as the motive power for the kind of self-assembly required and uses things like RNA, which still today creates its own transcriptive mechanism as well as several other utility enzymes, but the basic requirement is an energy gradient - beyond that, an awful lot of the chemical precursors to life seem to be self-assembling in the right conditions.
Now, if you want to argue about where exactly that transitions from self-propagating chemistry to actual Life occurs, that's a question for the philosophers - things get a bit muddy at that scale, but mechanistically, I'm not aware of a "missing link" in the early story of life.
Right, usually it's "speculative theories that we can assemble evidence for by building upon prior work and known facts about the world", which the hydrothermal vent theory is. "Science" when talking about "how did life form" will always be "speculative theories" until we crack the time-travel nut.
Science also requires a plausible mechanism and an understanding of statistics. "It must have randomly happened even though the chance was less than 1 in ten to the five hundred and twelfth" is about as far as these speculative theories have gotten so far.
Interesting looking book. I'll have to check it out. In my experience, discussing this material online tends to devolve into an atheist/theist debate. Both sides are very sure of themselves and it isn't about exploration and curiosity so it tends to turn off us more agnostic-minded people (or just those both open to abiogensis as well as other creative possibilities).
And these stories are just ripped from https://www.sciencenews.org/article/all-of-the-bases-in-dna-...
Folks with enough news bucks, please flag.
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