Storyline

This page details the events depicted in Subnautica in which they are presumed to be in the correct canonical order. All information is taken from in-game lore, and Developer statements.

=Base Game Story Events=

Precursor Period Events

 * Around 1000 years prior to the events of the game, the Precursor Race discovers Kharaa on an unknown planet and some individuals are infected. Errors in quarantine procedures cause Kharaa to be spread to their core worlds.
 * The Precursors set up several research outposts to attempt to develop a vaccine, including one on Planet 4546B. The Quarantine Enforcement Platform, the Disease Research Facility, and the Alien Thermal Plant are constructed, as well as the Sanctuary Caches. It can be assumed that around this time period, the Gargantuan Fossil was found, and the Precursors began taking samples from its ribcage.
 * After many tests, the Sea Emperor Leviathan species is found to have an immunity to Kharaa, and the Primary Containment Facility is constructed, along with the Alien Arch Caches in various biomes. The Precursors capture a 1600-year-old Sea Emperor Leviathan, along with its seven eggs and contain them within the facility. It is likely that this is also when the Ancient Skeleton was discovered, and the Lost River Laboratory Cache was constructed as the focus of this laboratory's study is Leviathans.
 * It is revealed to the Precursors that their captive is much too old. Due to this, the potency of its Enzyme 42 had declined, meaning it was not capable of killing the infection, only causing temporary remission. The Precursors then conclude to research its unborn eggs, as they deduced that a younger specimen would produce a stronger enzyme.
 * The Sea Emperor Leviathan telepathically telling the Precursors their methods of forcefully making the eggs hatch would not work though according to the Sea Emperor "they could not hear". The Precursors dissect one of the eggs and lay its fetus on an operating table, however, the process kills the fetus. A second egg is stored within the Primary Containment Facility's egg lab in order to research it. More eggs from the majority of the species on the planet are taken as well. The Precursors eventually place the remaining five eggs into the Incubator Device.
 * The Precursors take a Sea Dragon Leviathan egg for research on leviathan egg hatching conditions, due to the species' possible relation to each other. However the parent tracks down its egg and rams into the Disease Research Facility, destroying it. Kharaa is released and the Precursors initiate the planetary quarantine. Construction for the Warpers cease, leaving only limited number on the planet.
 * The Precursors deem the planet a lost cause due to Kharaa's severity, focusing on a vaccine rather than the spread of the bacterium. Kharaa kills a majority of species on the planet, rendering the ancestors of the creatures in the modern day to rapidly evolve due to the drastic changes in the ecosystem.
 * Remaining Precursors are evacuated to sanctuaries where their bodies are disposed of and their minds uploaded to data hubs.
 * The Sea Emperor Leviathan species is killed off due to their food source being wiped out by Kharaa, save for the one in containment.
 * The Sea Emperor Leviathan trains Peepers to use the Alien Vents, with each Peeper carrying small amounts of Enzyme 42 to distribute among the planet.
 * The Precursor species is presumably killed off by Kharaa sometime between 1200 AD and 2160 AD.

Degasi Period Events

 * Around 990 years later, the Degasi crashes on 4546B.
 * The Degasi survivors build their bases on the Floating Island, however, due to torrential rainfall and Marguerit's persistence, they relocate to the Jellyshroom Cave, and Marguerit uncovers a tablet.
 * The Degasi survivors relocate again to the Deep Grand Reef, where Bart explains to his father and Marguerit that they are infected with something. After Marguerit brings an injured Reaper Leviathan to the base, a second Reaper Leviathan, having followed Marguerit back, attacked and destroyed the base. Marguerit chased the creature, intent on killing it, whilst Paul followed a light he saw (possibly a Mesmer), Bart managed to elude the creature and fled to presumably the Safe Shallows or Crash Zone.
 * Bart manages to survive for an unspecified amount of time, able to build himself a Seabase and a Seamoth. Although he eventually fled to the Floating Island, where he wrote his final log, and most likely succumbs to Kharaa.

Aurora Period Events

 * A decade later, the Aurora attempts to perform a slingshot maneuver in the atmosphere of Planet 4546B with 157 people aboard. However, while doing so, the Quarantine Enforcement Platform detects the ship and fires at it, resulting in it crashing on 4546B, and the crew is forced to evacuate.
 * 29 to 44 people manage to eject in Lifepods 1-25, but only ten manage to make it to the surface, with only one carrying a dead passenger. Each Lifepod landed in different Biomes. One, in particular, is Lifepod 5, housing the Non-Essential Systems Maintenance Chief, Ryley Robinson. He is knocked unconscious for three hours by a loose panel during its descent. All the other surviving crew members perish during this period of unconsciousness.
 * The Aurora's drive core explodes.
 * After (arguably) one week, the Sunbeam picks up a distress call and comes to rescue Ryley.
 * The Sunbeam sends the coordinates for the Mountain Island, where they will land.
 * The Sunbeam is destroyed by the Quarantine Enforcement Platform, which Ryley explores, discovering Alien Tablets, the Control Room, and the approximate location of the Disease Research Facility.
 * After exploring the Mountain Island, Ryley finds the Alien Arch within, and activates it, taking him to the Floating Island, where he also discovers the Degasi Seabases.
 * Ryley goes to the Disease Research Facility, and discovers the nature of Kharaa and realizes that he is infected.
 * After the incubation period for Kharaa is finished (two weeks, at this time), the coordinates for the Alien Thermal Plant are received.
 * Ryley reaches the Alien Thermal Plant and attains the Blue Tablet, along with the Ion Battery and Ion Power Cell blueprints.
 * Ryley reaches the Primary Containment Facility and encounters the now 2600-year-old Sea Emperor Leviathan.
 * The Sea Emperor Leviathan telepathically communicates with Ryley and explains that its eggs must be hatched in order to eradicate Kharaa.
 * Ryley hatches the eggs after gathering various flora from different biomes using the Arches, and the Sea Emperor Leviathan Babies release the stable form of Enzyme 42, otherwise known as Baby Leviathan Enzymes. Ryley interacts with the Enzymes and is thus cured. After playing with their parent, the Babies leave the aquarium through the Arch behind the Incubator. Their parent stays behind as it is far too large to travel through the Arch, eventually, it dies here, though Ryley never sees this.
 * Ryley goes through the Aquarium Arch which is connected to an Arch on a suspended platform close to the Quarantine Enforcement Platform, he enters, and, now cured, is able to disable the weapon, allowing him to escape.
 * Ryley returns to the now-destroyed Aurora and obtains the Neptune Escape Rocket blueprint, where he eventually constructs it.
 * Ryley enters the rocket, and activates it, blasting off from Planet 4546B. While orbiting the planet, the Sea Emperor Leviathan communicates with Ryley one last time, just before he leaves the system, heading back to Earth.
 * He is then met with a notice that in order to land, he has to pay a 1,000,000,000,000 credits fee that he has accumulated by using the planet's resources.

Vesper Period Events

 * Ryley Robinson likely returns to Alterra.
 * Alterra learns of the value the planet holds.
 * The Vesper is installed in orbit for research.
 * Robin Goodall and Jo Jeffreys amongst other researchers are assigned to a research base in Sector Zero likely researching the local environment and investigating Precursor technology.

Unspecified Events

 * At an unspecified time, the Precursors obtain various relics from other alien races, including humankind, shown by the 13th century Earth sword and the Yin and Yang carving held in the Primary Containment Facility.
 * At one point, Earth dolphins became extinct.
 * A meteor struck 4546B sometime in the past in the Dunes biome. It is assumed that this occurred some time in the last 1,000 years as the Precursor cache in the crater has no normal entrance and one of the pillars has toppled, causing it to appear as if it has been destroyed by the meteor impact.
 * A new strain of Kharaa evolves the ability to control and alter the structure of living creatures, causing the events of Natural Selection and Natural Selection 2.
 * The Precursors construct the Warper out of various creatures from different planets. Whether this happened during their period on 4546B or prior, is unknown.
 * Between the events of Below Zero and Subnautica, Three Sea Emperor Leviathan Juveniles migrated to Sector Zero.

Non-Canonical Events

 * If Ryley disables the Quarantine Enforcement Platform before the Sunbeam arrives, the Sunbeam will survive, but he will still need to get the Rocket blueprint. This event is generally considered non-canon.

Trivia

 * Given that the Precursors likely obtained the Earth Sword around 1000 years ago, and the sword itself being of 13th century Mongolian design, it is likely that the Precursors visited Earth during the third crusade era (1189–1192). From this, it can be deduced that the game takes place in the timeframe of 2160-2199.