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Questions that don't need their own topics vol.2; New and fresh
Topic Started: Jan 4 2018, 11:18 AM (26,879 Views)
Sceynyos-yos
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I knew I had seen it from a more reputable source.
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Holben
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Sceynyos-yos
Mar 4 2018, 04:11 AM
So neither elevation in galactic plane, nor closeness to galactic center has effect to planetary habitability? I've heard that at least the latter is a factor, as supernovae and whatnot are more frequent near the center.
Some of the factors mentioned in Rare Earth regarding location in galaxy, with some more recent data tacked on:

Metallicity, affecting the likelihood of terrestrial planets. Our solar system is unusually metal rich, being an intermediate population 1 star (another kind, extreme population 1, are found in and around the galactic core), and even among thin disk stars it's quite high (average for thin disk across the galaxy is Fe/H of -0.5; in our area it's about -0.02 dex, which is near the peak for the whole disk). Recent research based on exoplanet surveys indicate this isn't as big a deal as they suggested, obviously caveat our current sampling bias, with small terrestrial planets being significantly less affected by metallicity compared to Jupiters. In fact, very high metallicity stars may be very risky, since they tend to form more Jupiters and be more likely to have hot Jupiters or cold eccentric gas giants, and eccentricity of these gas giants increases along with metallicity. However, solar-comparable metallicity could still be necessary if things like having a huge iron core are vital for life, and due to the need for radioactive elements to keep the planet warm. Stars at the galactic centre seem, based on recent observations, to have a huge variety of metallicities.

Orbit around the galaxy. Like most stars at our distance in the galactic arms, our solar system has a nice circular orbit around the galaxy. The galaxy isn't a point mass and we interact with loads of stuff as we go around, but as a constraint at any one time our eccentricity would only be a few percent. It's lower than the peak for local eccentricities, which puts us in a minority in our area, and is one of the Sun's several unusual features. A high eccentricity could result in entering more dangerous areas of the galaxy more frequently. The sun is close to the galaxy's co-rotation radius, which is where the angular speed of the galactic arms matches the speed of the stars comprising it, and so is the location where crossing over between spiral arms is least common. Spiral arms may be more dangerous due to higher stellar density, supernovae likelihood, and the presence of dense molecular clouds, so avoiding them might be a good thing. There are several stellar streams around us with similar orbits but it's very rare for the galaxy as a whole.

Stellar age. We live in a galaxy which has maintained star formation at a significant level to the present day, which is not at all universal, and allows later populations of metal rich stars. However, this isn't true for all parts of the galaxy. Halo stars and globular clusters are very old stars. Young stars are also poor candidates since they simply haven't had any time for much to happen, and we have to work with the assumption that it takes 4 billion years or so to reach multicellular life. The working assumption is that we want stars between 8 and 4 billion years in age- and the best places for that are the galactic centre and our back yard.

Galactic dangers. Some people talk down the importance of events like supernovae and GRBs here. But in papers like this one, the majority of stars are found to be under significant supernova flux during their lifetimes, with only 27-36% of stars remaining unsterilised. The peak for this activity is naturally in the galactic centre. At our distance, about 8 kpc, only between 36 and 53% of stars are unsterilised. And that is only one effect; gravitational perturbations are also a serious threat to planetary systems. Earth has had close calls in the past- about 70,000 years ago, a star passed through the Oort cloud about 0.8 ly from the sun. If anything had come much closer perhaps I wouldn't be writing this. Obviously, this threat scales with stellar density.

I'm drawing heavily on the paper I linked to in the last paragraph, but that paper also has some interesting and unanticipated conclusions. They find it conceivable that some habitable planets could exist at 2.5 kpc from the centre, and in fact because stars and planets are so much more numerous there they estimate that most habitable planets will exist in the region around that distance, which is at odds with the general idea that the ring marked by 7-9 kpc from the core is the most likely location for habitable planets. The importance of the bulge and the presence of many systems above and below the galactic plane in the inner galaxy is also important, since those systems may be less at risk of sterilisation events.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

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Rhinobot
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Would it be possible for a large group of organisms from the same biome on Earth to be brought to a planet without multicellular life and survive without assistance?
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For anyone who, like me, finds it hard to read much of the writing on the National Geographic image Sceynyos-yos posted, here is a link to the image location where it can be viewed at a larger size: https://cdnb.artstation.com/p/assets/images/images/009/627/629/large/antoine-collignon-1-2.jpg

Holben
 
Young stars are also poor candidates since they simply haven't had any time for much to happen, and we have to work with the assumption that it takes 4 billion years or so to reach multicellular life.
Do you mean 4 billion years from the first unicellular life to the first multicellular life, or 4 billion years from the planet's formation to the first multicellular life?
In the first case, it actually took significantly less than 4 billion years to go from the first unicellular to the first multicellular life. The earliest known single-celled microbes show up around 3.8 billion years ago, and the earliest unambiguous evidence for multicellular organisms show up around 700 million years ago if I'm not mistaken. So that's about 3.1 billion years to get multicellular life. There is, however, some controversial evidence for multicellular life as far back as 2.1 billion years ago, in which case it would've taken just 1.7 billion years to get multicellular life on Earth.
If you meant the time from the planet's formation to the first multicellular life we're talking 2.5-3.9 billion years, in which case your 4 billion year statement makes somewhat more sense.

That being said, it should also be noted that just because it took 1.7-3.1 billion years to go from the first unicellular to the first multicellular life (or 2.5-3.9 billion years from planet formation to the first multicellular life) here on Earth that doesn't mean it always needs to take so long on other worlds. With Earth as our only sample so far we have no way of knowing whether the time it took here is typical, exceptionally short, or exceptionally long. And even if it is typical, there's almost certainly gonna be some exceptions to the rule, especially when one considers that evolution has no plans for when anything will happen. So even then one could have some worlds where multicellular life gets started relatively early in the world's evolutionary history.


On supernovae being "sterilisation events", I must remain skeptical on this. That they could cause extinction events I have no problem with, but the idea that they doom all life seems to underestimate just how resilient life can be. Incidentally, it is possible (though not certain) that the Ordovician-Silurian Mass Extinction was caused by Earth being blasted by radiation from a supernova. If that is the case it is interesting to note that while a lot of things died out on Earth because of it, life still managed to make a full recovery. So even if there are worlds where getting blasted by supernovae is more common (and by "more common" we are still probably talking about millions of years between each time it happens) life could still recover from the resulting extinction events.
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Holben
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Mar 5 2018, 07:16 PM
If you meant the time from the planet's formation to the first multicellular life we're talking 2.5-3.9 billion years
Yes.

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Incidentally, it is possible (though not certain) that the Ordovician-Silurian Mass Extinction was caused by Earth being blasted by radiation from a supernova.
There was speculation about a GRB triggering its beginning, but no evidence has turned up for that and it fits really well with what you would expect given what was happening with the continents at that time. It's a nice idea but it's not necessary or supported by any data.

There are similar arguments about an event (this time known from isotopic data) about 3 million years ago and located 150 ly away or so causing major climactic change and possibly even beginning the cooling around that time, though again there is a geographical explanation that covers the issue.

These events are very distant supernovae, all things considered. Radiation flux follows the inverse square law, so the flux from 1a at 25 ly would be expected to be 36 times more intense than the 3 Ma event, and so on. A 1a supernova at 5.5 ly would be as bright as the sun after t+19 days, producing days twice as bright and with twice the incident thermal energy if it was in the same hemisphere as the sun, which would take 60 days to reduce to 10% original brightness. Even ignoring the effects of hard radiation and cosmic rays, I think it can be seen pretty easily how that could be significant. 1a supernovae are of middling strength as they go, with some types up to five times more energetic.

Subterranean microbiota would likely survive pretty well in the above scenario, but for photosynthetic organisms for example the story would be very different, and the Rare Earth hypothesis has no issue with microbiota being found all over the shop.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

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Have fossilized gallstones, kidney stones or other calculus ever been found?
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lamna
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Does anyone know a good source for information on the evolution of Paleozoic invertebrates? I can't find anything beyond the the basics, I really want to know about the insects and land gastropods.
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lamna
Mar 5 2018, 05:12 AM
Does anyone know why Bison is still a valid genus? Bison are obviously very close to Bos cattle, even capable of producing fertile hybrids. But I don't see anyone going over to Bos bonasus or Bos bison.
Since genera is so blatantly arbitrary, it really just boils down to people deciding they want a split rather than lumped Bison and stick with the tradition instead of changing it.
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Motile larvae of sessile terrestrial organisms is a concept that I have been playing about with in my head and as such, I wanted to ask some questions. Terrestrial photosynthesisers often don't produce enough energy for significant movement, thus would it even be evolutionarily practical/beneficial to waste their own resources to create a singular highly active offspring as opposed to many less active ones? Would it be beneficial to release them right into the ground and let them be detrivorous like earthworms?
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This is a topic I have considered a lot as well.

I think the existence of fruit (and nectar-filled flowers) proves that plants are willing to invest quite a bit of energy into reproduction. The fruit typically has to be rich enough in energy to be appetizing to large animals with high metabolisms. I don’t see tiny moving seeds resembling bugs or worms being more energy intensive than the production of dozens of fruits, and they would be a far more precise method of dispersal than relying upon the whims of animals. Of course, these seeds would have to worry about predators, so I’d imagine plants with mobile seeds deploying them all at once so as to overwhelm the opposition. Overall, I don’t see the production of small, mobile larvae being a less efficient alternative to using fruits.

I think partially-heterotrophic seeds could be effective, especially if they could consume organic matter and, perhaps, nearby plants so as to eliminate competition.
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lamna
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Nectar is, as far as I understand, pretty cheap for plants to produce. It's literally water and sugar. All plants need for that is sunlight, air and water.

Fruit is more of an investment, but still most fruit is basically just sugar. Sugar is valued by many animals because it is very easy to break down. Barely any time is needed for digestion, so you don't have to hang around with a big heavy gut full of food.

I'm not dismissing the idea out of hand, plenty of plants reproduce in very energy intensive ways. The coco de mer produces a coconut that can weigh up to thirty kilograms (that's as much as eight year old human child), the nut takes six or seven years to grow, then another two to germinate.

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Nonetheless, the sugar used in nectar and fruit is sugar that could be used for other purposes.

According to a five minute web search, a typical coconut contains approximately 1,400 calories, and a healthy tree yields over seventy a year. Let’s say that these hypothetical “plantimals” produce literal hummingbird seeds, whose sole purpose is to travel far away from the parent plant and land in suitable ground, perhaps using any stored energy as a means of boosting growth as a vegetable.

Ignoring how this evolved (I’m using hummingbirds as an example because they have an extremely high metabolism and as such would represent as worst case scenario regarding energy concerns), these seeds would need, at most, ten calories a day, and, factoring in the period of growth and energy needed during the journey, these seeds would require at a maximum around 50 calories to produce.

If I’m not being a complete idiot and calories are a decent measure of the amount of energy an organism requires to be grown by another, a hypothetical plant could produce 30 hummingbirds instead of a singular coconut. These seeds would be fast, maneuverable, and very difficult for predators to catch, and they only cost half the calories, or energy, of a traditional fruit, such as an apple, which is 100 calories. Of course, fruits today are selectively-bred to produce massive fruit, so I imagine the naturally-evolved apples were significantly “cheaper” to make.

If any of this is wrong (it probably is) please tell me. There are a ton of factors that I didn’t take into account, many of which could shift the energy balance toward producing large fruits. Maybe I’m being really stupid here and just don’t know what I’m taking about, but I think it’s an interesting thought.

Also, that coco de mer seed is insane!
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If you were to place these two species in the same alien environment and they competed against each other, which would become more successful and speciate more effectively given enough time; the house mouse or brown rat? I know both are quick breeding and adaptable species but I'm not sure which one can perform better than the other given enough time (say a few thousand years at least, or if it need be several million)
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Sceynyos-yos
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Mar 8 2018, 02:53 PM
Nonetheless, the sugar used in nectar and fruit is sugar that could be used for other purposes.

According to a five minute web search, a typical coconut contains approximately 1,400 calories, and a healthy tree yields over seventy a year. Let’s say that these hypothetical “plantimals” produce literal hummingbird seeds, whose sole purpose is to travel far away from the parent plant and land in suitable ground, perhaps using any stored energy as a means of boosting growth as a vegetable.

Ignoring how this evolved (I’m using hummingbirds as an example because they have an extremely high metabolism and as such would represent as worst case scenario regarding energy concerns), these seeds would need, at most, ten calories a day, and, factoring in the period of growth and energy needed during the journey, these seeds would require at a maximum around 50 calories to produce.

If I’m not being a complete idiot and calories are a decent measure of the amount of energy an organism requires to be grown by another, a hypothetical plant could produce 30 hummingbirds instead of a singular coconut. These seeds would be fast, maneuverable, and very difficult for predators to catch, and they only cost half the calories, or energy, of a traditional fruit, such as an apple, which is 100 calories. Of course, fruits today are selectively-bred to produce massive fruit, so I imagine the naturally-evolved apples were significantly “cheaper” to make.

If any of this is wrong (it probably is) please tell me. There are a ton of factors that I didn’t take into account, many of which could shift the energy balance toward producing large fruits. Maybe I’m being really stupid here and just don’t know what I’m taking about, but I think it’s an interesting thought.

Also, that coco de mer seed is insane!
You'd also have to grow muscles, bones and all that too, though. I don't know how cheap protein is to make.
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Well lots of plants make protein. I know this because I know a lot about potatoes. A potato contains 4.3 grams of protein (I like mine with raisins). Potatoes help keep me healthy and strong! So maybe the fruit could move.

Does anyone know how long it would take potatoes to turn into animals? What if there were no other animals on their planet?
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