Plates are massive accumulations of Grey Kelp.  They vary in size, but the largest are dozens or hundreds of miles wide and nearly a mile thick.  Older plates tend to accumulate a layer of topsoil.  Grey Kelp is highly nutritious to plants, and transplanted plantlife, although not native to Thresher, often grows quickly on the topside of a Grey Kelp plate.  After hundreds of years, a layer of topsoil develops, furthering plant growth.  The topsides of plates vary as much as natural terrain on land, with hills, valleys, plains, rivers, and even snowcapped mountains and cliffs being present.

Settlers on plates often bring plant and animal life with them to make their lives easier.  Forests are planted, crops such as wheats, and even decorative plants are brought to the plates.  Some plants are also brought accidentally, and after hundreds of years a plates ecosystem is hard to distinguish from that of a normal piece of land, although large land predators are rate.  Animals are also introduced in a similar way.  Cattle, horses, pigs, goats, sheep, even deer are brought by settlers, with some getting loose and going feral.

Birds, able to move from plate to plate on their own power, are the most common life across plates of all ages, and they are the most resilient against subsummation.

Subsummation, the process by which a plate falls into the fiery core of Thresher, is not uncommon, but, given the size of Thresher, will most likely attract attention at least in the local area.  Plates subsume for a variety of reasons.  Collisions with other plates can cause a lose in buoyancy.  Sometimes a plate will merely settle to a lower, but habitable, altitude (although the hotter weather can often cause catastrophic climate change on the plate), but other times the increased heat will cause a loss in lifting gas, creating a self-reinforcing cycle and quick causing the plate to lose altitude more and more until it is destroyed by the heat of Thresher's lower layers.  Storms are also a huge danger to plates, and given that storms on Thresher can last for millennia, a single storm can claim dozens of plates as its winds break them apart, or at the least scour them of life.