Recent comments in /f/askscience

being_interesting0 t1_j8gtbeo wrote

Reply to Is it possible that abiogenesis is still happening right now on earth? by dolekanteel

No. 2 reasons.

  1. Life is a winner take all phenomenon. Once life has overtaken and adapted to an ecological niche, it would be very hard for something new to evolve there that was better adapted

  2. There is a hypothesis that the first chemical steps in abiogenesis required an earth with no or low oxygen. Nick Lane talks about this in some of his books (highly recommend)

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PopeBrendicus t1_j8gtb4h wrote

Reply to Is it possible that abiogenesis is still happening right now on earth? by dolekanteel

Not my area of expertise so someone may correct me later on, but the prevailing theory is that all life is descended from a single abiogenesis event, mainly because any life we have found evidence of has functioned exactly the same (well, basically) as things alive today. No one sticks out enough to say "yeah, that's funky, that doesn't work the same as everyone else"

I highly recommend Life's Edge by Carl Zimmer for an interesting read on this topic, because a lot of the questions you're asking depend on the very-much-disagreed-upon definition of "life." There are still scientists looking for signs of abiogenesis, in labs and in the field (particularly around volcanos, hot springs, thermal vents, etc, because that's what Earth used to be like).

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the_j4k3 t1_j8gswms wrote

Reply to Is it possible that abiogenesis is still happening right now on earth? by dolekanteel

I think anything novel must compete with well adapted, established organisms using a limited set of resources that the existing organisms recognize as food.

I believe there must have been more than one abiogenesis in the beginning, but only one was ultimately successful. Kinda like how there were many branches of Homo, but we are the only ones still around. I can't picture a scenario where one chance encounter leads to life as we know it. I can picture a situation where the conditions were conducive for life, many were nearly there, several would be defined as life now, and only one found success and dominated.

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MsPennyP t1_j8grp80 wrote

Reply to Is it true the humans could breathe and live in the atmosphere of Venus? by Impossible_Mine_1616

No. Human life could not exist anywhere in/on Vensus' atmosphere. Venus has a thick, toxic atmosphere filled with carbon dioxide and it's perpetually shrouded in thick, yellowish clouds of sulfuric acid that trap heat, causing a runaway greenhouse effect. It's the hottest planet in our solar system, even though Mercury is closer to the Sun.

What "life" could possibly exist there would be some bacteria in the uppermost cloud tops. But even then it would need to be hyper acidophilic due to the concentrated sulfuric acid there.

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masterofshadows t1_j8gp7z2 wrote

Reply to comment by Weed_O_Whirler in Light traveling through a medium that slows it. Does the same photon emerge? by TheGandPTurtle

>elementary particles are all fungible. That means, they are truly identical, and they are impossible to label. So, if a photon is absorbed and then remitted, it doesn't really make sense to say "is it the same photon or a different one?" There aren't really "same" or "different" photons, there's just photons, unlabeled.

So then do we know for sure photons actually move and don't just vibrate or something causing the next one in the chain to vibrate or something like that? Kind of how AC current works except with photons?

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Weed_O_Whirler t1_j8gn3wr wrote

Reply to comment by dack42 in Light traveling through a medium that slows it. Does the same photon emerge? by TheGandPTurtle

While it's true if a single photon is absorbed by a single atom, you cannot predict which direction the photon will be re-emitted, so how is this different? Well, the process is not so different from light "reflecting" off a mirror- while we say light reflects, a mirror is also an absorption and re-emission situation, and obviously those don't go in a random direction.

The answer comes down to conservation of momentum and interference. Since the incoming photon has momentum, there is a higher probability that the photon will be emitted in the same direction to conserve momentum. Obviously, not all of the photons are emitted in that direction, but due to the probability there will be constructive interference in the same direction and destructive in all other directions. In general, things like Snell's Law of Refraction, and angle of incidence equalling angle of reflection occur with large numbers of photons, and they do not describe what happens when a single photon is absorbed.

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