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Yes... But no. As mentioned already, direct factors include gravity and available biomass. It is important to remember that the rules are different for marine, terrestrial and aerial ecosystems. Marine ecosystems enable larger organisms because the bouyancy force of water negates most of an animals weight. This allows huge amounts of plankton and algae to ...


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It's reasonable to say that climate is what limits the size of current organisms on Earth, because we know that in past climates, many kinds of organism grew much larger: 70cm dragonflies, 15m sharks, 2ton rats, etc. If the size of the planet is not what limits the size of organisms today, there's no reason to assume it was the limit in the Cretaceous ...


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Basically, yes: the less Mass, the easier it is to get big. So there is an inverse relation. Big things need to eat either lots of small things or other (not quite so) big things, unless they are parasitic or predators in which they can live off bigger things. A major driving force for the sheer quantity of biomass required for super large animals is always ...


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Necessary premise: we are talking about a sample with size 1, since at the time I am writing it we know only one planet hosting life. The main effects the size of a planet might have on the maximum size of its life form is directly due to gravity, and indirectly due to the biomes supporting the large life forms. Gravity: obviously, the stronger the gravity ...


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A magnetic field and geothermal heat are not necessarily interdependent. If you have a molten core of magnetic element (iron and nickel in Earth case) then the dependence is present. But if your core is molten and not magnetic, you have the heat without the magnetic field. Moreover, you can have geothermal heat as a consequence of tidal forces, without ...


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If we're talking a tidally locked world, there is a belt around the planet that is perpetually twilight. It's not the whole planet, but that is a fair bit of real estate that never stops being twilight/dusk. There's also an interesting wrinkle you can add to this. This isn't a uniform brightness to the night sky, but there is actually a way to have a ...


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You write: One planet is pretty much a perfect copy of Earth and the other planet is 20% less massive with a radius 10% smaller. So the smaller planet has 0.90 of the radius of Earth and 0.80 of the mass of Earth. A planet with 0.9 the radius of Earth should have a volume of 0.729 the volume of Earth. If its average density was equal to that of Earth, it ...


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That is not stable over geological time. Systems like Pluto and Charon require one to be much more massive than the other so that their orbits don't intersect. If the masses are the same, it may take some millions of years but the planets will collide. That's because any slight perturbation in their orbit will cause one planet to go to a very slightly lower ...


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Gamma ray burst. https://supernova.eso.org/exhibition/1217/ These are energetic sudden emissions that radiate with the force of many suns. One nearby to us would be tough if the beam hit earth. https://en.wikipedia.org/wiki/Gamma-ray_burst#Hypothetical_effects_on_Earth_in_the_past Hypothetical effects on Earth in the past[edit] GRBs close enough to affect ...


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The climate was already at a tipping point, when one or several catastrophes happened: a solar superstorm, an impact or whatever. After the catastrophes the planet slode into an almost irreversible greenhouse trap, i. e. the planet got cooked. Changes in chemistry made the rocks gas out a lot leading to a Venus-like environment with high pressures and ...


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High exposure to UV radiation, presumably due to a solar event or a man-made event. UV causes DNA to mutate. Complex organisms with be disproportionately affected, one can imagine only a few specialised unicellular organisms with enough shielding against the radiation make it. High temperature could also be used, again only thermophiles will make it. The ...


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Just so you know, when Earth was formed it was very Venus'y at the beginning. Then when it was finally cooling down Theia came and reset the Hadean era, possibly extinguishing early bacterial life. Some millions of years later Earth cooled again and billions of years later here we are. A new giant impact could lead to a new Hadean era. It could probably wipe ...


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Not an exact match for venus, but close is plausible. The start is global warming 101: Silly civilisation emits lots of CO$_2$. Hot weather melts frozen CO$_2$ and methane deposits. Runaway greenhouse effect cooks the planet. Over the following million years another Great oxygenation event happens. Simple organisms undergo photosynthesis. Few cycles of ...


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Scientists think that 3 and a half billion years ago on Earth that the oceans were once purple. As chlorophyll hadn't been developed yet ancient photosynthesisers used other chemicals that had a purple pigment rather than a green one. There is one caveat in this hypothesis if you want your world to support intelligent life and a purple ocean. The purple ...


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Both are very easy. Fields can without doubt be golden-yellow on Earth too. Nothing to invent there. Seas are only marginally more difficult (I am on record as saying otherwise some eighteen years ago, but the scenario is quite different). You can have algae or cyanobacteria thriving in the photic zone (first, say, 50m of depth). These can be almost any ...


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