Any sort of floating ground that could harbor life was the first
That's easier than rocks.
Mars size world orbiting a gas giant. To terraform it, mass off the gas giants atmosphere are blown off, turned to plasma and dumped on the moon. Atmosphere is mostly helium and large amounts of fluorocarbon to create a greenhouse effect and maintain atmosphere for few hundred thousand years. Atmospheric density is 2-3 times that of earth but mostly inert save for the trace nitrogen, CO2 and oxygen, which at those pressures is easily breathable in small quanties
Problems are encounter as the planet warms because vast amounts of CO2 and ice are part of the structural geology on a planet that has never thawed. As it warms, the ground heaves, erupts and slides randomly and catastrophically in pyroclastic flows flows that crush and smother every living thing. The same effect causes sudden vast sink hole to suddenly collapse. Lower areas can be flooded with asphyxiating CO2 flowing from high lands with no warning.
Ground winds are very dangerous. The winds pack 2-3 times the kinetic punch as the same velocity wind on earth. Worse, the low gravity makes it easiy to pick up dust and even pebbles. Fortunately, the thick atmosphere transfer heat around efficiently so such storms tend to be localized.
The surface is to dangerous to live on permanently.
The 1/3 earth gravity and 2-3 times atmosphere makes flight much easier. The solution for colonist is to engineer plants-like organism that grow up into free floating balloons. Sometimes tether, other times floating. Their buoyancy comes from having pure helium inside which they heat with solar radiation. They don't gain a lot of altitude just enough to say about the chaotic landscape.
Although plant like, they have some animal attributes in needing to sense the environment and move accordingly
They have a long tail of lightweight tendrils they use to anchor when needed but keeps them stable the rest. At the top they are disk shape with gas cells radiating out like large flower petals. The petal provide compact photosynthesis by employing the entire exterior membrane as the chromoplast. The flat shape provides active support on the dense atmosphere and in the wind provides lift. There top center forms either a convex dome shape or concave bowl shape.
They look somewhat like a sunflower with very large, rather thick translucent green leaves sticking out. They can reach the size of major sports stadium with a dome area 300 meters in diameter and 600 meters of leaf shaped lift cell radiating outward.
On the dome or bowl shape, is a lichen that serves as a thin but effective soil/anchor for various plant species. Humans live and farm on the "islands".
Flight in the thick atmosphere is very easy. Humans can almost flap of the ground with large wings (but not quite.) Airships need gas bags only a third of that on earth. Wings as well are small. Steam engines provide enough energy for flight. Glider work very well, can cover long distance and carry fairly significant pay loads.
The ground is treacherous and every shifting, with howling winds. Most human stay up in the sky, farming the islands and traveling by air. Coming down to the surface only to mine and build heavy industry. People who tough it out on the ground are nomadic and increasingly rely on raiding as they can't stay in one place long enough to plant or built anything.
There you go, floating island that would feel like rock when you stood on them. Stream powered airships, chaotic shifting earth below, mad barbarians lurking.