The sci-fi adventure film "After Earth," a kind of family affair starring Will Smith and his son Jaden Smith, is really two movies in one. The film's bookend segments are set aboard interstellar spacecraft with high-tech gadgetry, a thousand or so years into the future.
But the film's middle passages involve conjecture on biology, ecology and a particularly intriguing premise: What would happen if the Earth, as an organism, evolved to defend itself against the harmful human species? We take a look at the film's blend of biological and technological fiction to see if there's any basis in reality.
Fiction: In several early scenes, Kitai is seen running through beautiful but deadly forest glades in which predatory plants appear to have limited movement and even locomotion.
Science: There are more than 400 known species of carnivorous plants -- or more accurately, insectovorous plants -- which consume their prey through a chemical process similar to digestion. All plants move, of course, but usually too slowly to be discerned without the help of time-lapse photography. But there are exceptions: Several underwater plant species move about visibly, in still water, and the famous Venus fly trap snaps shut in less than half a second when capturing its prey.
Fiction: In the film, Kitai discovers that the Earth's atmosphere has adapted in at least one specific way to discourage human habitation -- there's not enough oxygen to survive. So he must use a futuristic inhaler which, his father explains, will coat his lungs and boost oxygen absorption.
Science: Modern asthma inhalers don't technically increase oxygen absorption into the bloodstream, but they do facilitate lung function by way of two main types of aerosolized medication: Bronchodilators relax muscle constriction, and anti-inflammatory agents suppress inflammation.
Fiction: The alien menace in 'After Earth' is a vicious-but-blind creature that tracks its prey by smelling fear. In the image above, a young Kitai avoids detection by hiding in an airtight plastic bubble.
Science: It's true that, as the old adage goes, animals can smell fear -- by way of airborne pheromones and chemoreception. But pheromones communicate information and effect behavior among animals of the same species. There's no evidence to suggest that a predator could use pheromone secretions to track prey from an entirely different species. Or, in this case, a different planet.
Fiction: Kitai's futuristic spacesuit has chameleon-like properties that allow it to match the color and texture of its surroundings.
Science: The suit in the film is a super-advanced example of electrochromism, in which materials change color when an electric charge is applied, plus biomemetics -- technology that imitates nature. In 2012, researchers at the University of Bristol developed a material that uses artificial muscles to mimic the color-changing properties of squid.
Fiction: In one harrowing sequence early in the film, Kitai is bitten by a giant venomous leech. The poison threatens to kill him within minutes unless an antivenom is administered.
Science: There are more than 600 known species of leech, but none are known to be venomous. Most major animal phyla contain venomous species, however. The leech is part of the Annelid phylum, which does contain several venomous marine worms. Many of the planet's most deadly animals have fast-acting venoms that can indeed kill within minutes.
Fiction: Kitai uses a wrist-mounted communication and navigation device to orient himself and check in with dad.
Science: Wrist-mounted computers -- a kind of subset of the wearable computer idea -- have been around since the early 1990s. Several commercial models have been brought to market with little success. Various forms of wearable computers with wrist-mounted displays are used in military and certain industrial capacities.
Fiction: In one of the film's more implausible concepts, Earth has adapted to discourage human habitation by freezing over completely, each and every night. To survive, Kitai must find geothermal "hot spots" whenever the sun goes down.
Science: The kind of deep-freeze scenario presented in the film would seem to discourage, with extreme prejudice, all plant and animal life. Still, the meteorological record does feature some pretty wild temperature swings. In 1911, the temperature in Rapid City, S.D., dropped from 55 degrees Fahrenheit to 8 degrees in about 15 minutes. The largest 24-hour temperature change in the United States was recorded in Browning, Mont., in 1916 -- from 44 degrees to minus-56 degrees.