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I’m working on a speculative evolution world on a Europa-like moon. It’s about 2/3rd the mass of earth orbiting a rogue Jovian planet about 5x larger than Jupiter. Around 400 million years after multicellular life appeared, the planet found itself in a stable orbit around a star in the habitable zone. The icy surface of the moon melted, releasing trapped gasses in the ice sheet and from the water, causing a worldwide deoxygenation, killing about 70-75% of all life. After this happened, a massive evolutionary rebound occurred to fill all the new niches. Many different clades of flora evolved to float on the surface (plants had already previously evolved to be disconnected from the ground) and evolved to attach to eachother to make reproduction easier, over time evolving into a massive super organism the size of South America. Fauna would then evolve to live around it for food, with some evolving to escape onto the surface for a time, over time evolving lungs and living permanently on land.

One problem I’ve realized is that things will fall off the organism, sinking to the bottom of the ocean, which is 40 miles down. Over large spans of time, this will accumulate until it loses most of its resources.

One solution I’ve come up with for this is convection currents bringing sediment from the ocean floor to its surface. Hydrothermal vents heat up the water, which then rises to the top where is then taken in by fish and plants, where it can then be used.

Could convection currents even make it that far up, or would they begin descending beforehand? And even if they could, would they be strong enough to bring sediment with them?

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  • $\begingroup$ I'm not certain why they would need to. Can you clarify what is in the sediment that the super-plant might not be able to get elsewhere? Presumably not inorganic matter like quartz. $\endgroup$ Commented 3 hours ago
  • $\begingroup$ @Escapeddentalpatient. If something heavier than water sinks to the bottom, chemicals within that object are lost. This would include heavier elements like iron, magnesium, calcium, and many others from animals falling and sinking, and while some will be caught by fish living in the water, some will get to the bottom. Same thing with some chemicals, for example, quartz is a necessary component to some plants, as their photosynthetic organelles evolved from kinetosynthetic organelles, and integrate the quartz previously required for kinetosynthesis into photosynthesis. $\endgroup$ Commented 3 hours ago
  • $\begingroup$ What are those "convection currents" which are supposed to carry stuff 40 miles up? Here on Earth the temperature of the ocean water is basically constant below 1000 meters depth. $\endgroup$ Commented 2 hours ago

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Very fine grained sediment can travel long distances, see for example this paper: MacDonald, Lee & Coe, Drew. (2007). Influence of Headwater Streams on Downstream Reaches in Forested Areas. Forest Sciences. 53. 10.1093/forestscience/53.2.148.

There you can find this chart

chart showing traveled distance vs particle size

where you can see that particles the size of 50 micron can travel up to 100 km with the right conditions.

If you want a more striking evidence, look at this satellite image

satellite image showing muddy water carried by a river extending into the ocean

showing muddy water (in other words, water carrying very fine particles) reaching up to 60 km from the shore.

Long story short, if your convection current is energetic enough, it can carry matter very far.

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  • $\begingroup$ The question is about "convection currents", whatever they may be, carrying sediment 40 miles up from the bottom of the ocean to the surface. Here on Earth oceanic ecosystems sometimes rely on upwelling to get nutrients from the deep-ish ocean to the surface, but I've never heard of anything travelling up to the surface from the really deep ocean floor, with the effect being seemingly limited to a maximum of less than 1 (one) mile of vertical distance and most often no deeper than 400 meters (1/4 of a mile). $\endgroup$ Commented 2 hours ago
  • $\begingroup$ @AlexP that's why I say "if the current is energetic enough". Reportedly bomber crews saw wooden beam carried up at their cruise level by the updraft when they were flying over the firestorms they had caused upon German and Japanese cities $\endgroup$ Commented 2 hours ago

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