There are two great moments in the history of life that should always inform the science fiction of human space travel and settlement. One is when life made the huge leap from prokaryotic cells, which are mostly simple and very tiny, to eukaryotic cells, which are very large and complex. In a number of the books by late biologist Lynn Margulis, the differences between these types of cells are repeatedly stressed. The distance from one to the other was, for her, more impressive than the distance between eukaryotes and the animals and plants, both of which are composed of eukaryotic cells.

The other great moment was life's movement from water to land. Margulis thought this development even surpassed dreams of the human colonization of Mars. Life, which probably started in hydrothermal vents in the bottom of oceans (the Water World Hypthosis), had to change radically to adapt to this new and dry environment. The seas offered protection and immediate access to the medium of life, water. The bodies of plants and animals are basically terra-suits for life on the harsh planet of land. Make the wood of a huge tree transparent, and you will see treads of water moving from the ground to the sky.

The only science fiction TV show that seems to have a sense or an idea of the enormous challenges of colonizing space is The Expanse, which is now in its third season, and which had on Wednesday, May 2, one of its best episodes, "Reload." Only half of the show's season two is interesting (this can be blamed on bad writing); and the whole of season one is, like Battlestar Galactica (from season one to three—the New Caprica sequence), a masterpiece of TV sci-fi. In fact, The Expanse is to this decade what Battlestar Galactica was to the previous one. But almost all of the science in the latter was bad (the show found its success in the fictionalization of an existential dread or mood that real humans could never really know or understand—planetlessness), where as a lot of the science in the former is respectable.

Plants are in the spaceships and bases of The Expanse. (There are none in Battlestar Galactica, though there is a lot of alcohol, an addiction to which is attributed to the bad mood of planetlessness.) Space travel or habitation has permanent effects on the human body—the more you are in zero-gravity space or low-gravity planets and moons like Ganymede, the more jelly-like you become. When humans from Mars (one of the two human colonies, the other is on the asteroid belt—these humans are called Belters) visit Earth, they have great difficulty dealing with the brilliance of its closer sun. The increased gravity also gets them. They collapse and vomit when they first feel it. Mars has 38 percent of Earth's gravity, which means a 68-pound Martian suddenly weighs 200 pounds on Earth. (I was informed by a deeper reader of science fiction that these features are found in the books the show is based on.)

The humans in The Expanse have, however, mentally adapted to the vast and empty spaces of space. There really is not that much out there (the show understands this!), which is why the spaceships do not have windows. Data-active flat screens are in the cockpit of the show's main spaceship, Contorta (it used to be called Rocinante but a horticulturist changed it in the first episode of the current season to honor a class of pine trees named Pinus contorta—their cones only release seeds during a fire). What is there to look at in space? Ninety-nine percent of the matter in our solar system is the sun. The moons and planets, the comets and asteroids are in the remaining one percent.

Life in space is hard. People are constantly fixing things, welding things, building things, keeping track of equipment and supplies. They often wear the sea and atmosphere (spacesuits) and spacewalk to perform repairs. A small mistake can be catastrophic. As the sad-faced horticulturist, Meng, pointed out in season two's episode "Cascade," there is not enough complexity in space, and so, if something goes wrong, it can be transmitted through a system very easily. Martians and Belters hate Earthlings because they have it so easy. The ecosystem services are already there for them. They do not have to worry about water or oxygen or obtaining a decent cup of coffee. But Martians and Belters are a proud people. And they don't drink booze to cope with dread, like the humans in Battlestar Galactica. They drink to have fun. They also like fucking in zero-gravity. They are, to use the words of Key-Matic, a brand new race.