Earth can be just all land, but we wouldn’t be here. It would be inhospitable to complex life. Surprisingly, though, there is a theory that a planet with just seas or lakes of water and without oceans might be more hospitable to microbial life if its orbit is outside the habitable zone in which liquid water can persist on the surface of Earth-like planets.

Water vapor is a greenhouse gas, and if there is less of it, a planet would be more resistant to the greenhouse effect, which could make it too hot if it’s closer to its star than the habitable zone of continental Earth-like planets.

This effect is so strong that such a desert world could still be habitable if it were only half as far from its star as our planet is from the Sun, assuming that the star was also similar.

Unfortunately, without plate tectonics, there would be no carbon or other elements necessary for life cycles. They would get locked into the crust and become unavailable to more advanced organisms that have more complex needs.

Nevertheless, microbes could still be found on such a world, and because vast deserts would separate each inland sea, there would be unique biospheres of indigenous life in each water expanse.

Since we have a desert planet in our system—Mars, maybe such exoplanets are widespread in the universe, and some could host life even in seemingly inhospitable orbits. Mars lost liquid water on its surface, but had it in the past. It wasn’t massive enough to hold on to its seas.

An all-land world with just some inland seas and more similar in size to Earth could be a fascinating destination for exploration if we ever find a way to visit nearby star systems.