# Conditions for intelligent and diverse life at high altitudes

I'm making a planet which hosts three distinct layers of floating islands, each higher than the last one. The islands should be reasonably thick, ranging from a couple hundred metres to three or four kilometres in average, depending on the size of the island and its relief. The layers need some separation between them of course. Taking all of this into account, it's notable the planet is going to need a lot of vertical space, furthermore, inhabitable vertical space, as the islands should house all kinds of lifeforms.

I've been playing around with Artifexian's "Earth-like atmospheres" spreadsheet of this video of his and tuned the planet so, with a similar composition to that of Earth's atmosphere, lower gravity and 4,2atm of pressure at planet's surface, we get a pressure of ~0,9atm at an altitude of 15km, which I think should do the trick for the most part.

Could complex life exist and develop in such high altitudes? Would the difference in pressure prevent life from the surface from living on the high islands and viceversa?

I'm sure there are a lot of important factors that make a difference as altitude increases I'm ignoring, like temperature decrease, solar radiation, wind currents and more. Please do point these out so I can take them into consideration.

Note that the lifeforms considered in this scenario are adapted to the conditions of their place of origin on the planet and do not strictly follow human endurance limitations when it comes to adapting to harsh conditions (i.e.: minimum and maximum oxygen partial pressure). With that said, human limitations may be used as a guide.

• Is this earth with floating islands? Because why are they different? I like the idea of a gas giant with a stratified atmosphere that was different at different altitudes. Life would be different depending on constituents of the atmosphere on a given level. Mar 27 at 18:57
• @Willk despite being Earth-like, the planet in question isn't a tuned up Earth, it is a different planet, with higher mass, a bigger radius, lower gravity (around 0,86g) and 4,2atm at sea level. The gas giant idea is cool, but the planet we are dealing with here isn't one. Plus I'd like (if possible) for there to be movement of living things among layers, so the conditions shouldn't be absolutely dividing from a layer to another. Mar 27 at 19:38
• What about your planet's star? All of these answers are modeled upon a sun like star. Different size stars have different UV output and could theoretically fudge the habitability one way or another. Smaller stars put out less UV so plants/life may br able to survive at higher altitudes. Note:UV is just one factor in play here that determines plant growth. Apr 26 at 23:39
• @Hippeus_Lancer That would be an F9 star with values relative to the Sun's of 1.120 (mass), 1.086 (radius) and 1.487 (luminosity) Apr 27 at 11:21

Altitude can be a proxy for latitude.

You can design your floating island ecosystems by thinking about ecosystems from varying latitudes on Earth. In places where there are big altitude differences this is how ecosystems work. A rise in altitude is a proxy for an increase in latitude - going up in elevation is like moving away from the equator and toward the poles. An example is the Sierra in Ecuador which is on the equator.