This page details the events depicted in Subnautica and Subnautica: Below Zero in what is presumed to be the correct canonical order. Some players might encounter the events in a different order, but the general story is still unaffected. All information is taken from in-game lore and developer statements.
- At some point, Earth dolphins become extinct.
- The Architects discover the Kharaa Bacterium on an outer planet during a routine network expansion. A network error caused the Architects' routine quarantine procedure to fail, resulting in at least 143 billion deaths on their core worlds. The Architects quarantined their core worlds and brought Kharaa to isolated disease research facilities, including on Planet 4546B, in order to research and develop a cure. The Architects construct the Quarantine Enforcement Platform, Disease Research Facility, Alien Thermal Plant, and Sanctuary Caches and begin constructing Warpers (whether this was the first time Warpers were constructed is unknown). It is believed the Architects also discovered the Gargantuan Fossil around this time and began to take samples from its rib cage.
- A meteorite strikes 4546B in the Dunes biome. The resulting crater blocks the entrance to the Architect cache and the impact toppled one of the cache's pillars.
- The Architects discover the Sea Emperor Leviathan species produces Enzyme 42, a compound that provides immunity to Kharaa. They construct the Primary Containment Facility and Alien Arch Caches. They capture a 1600-year-old Sea Emperor Leviathan and her seven eggs and place them in the Primary Containment Facility. It is believed the Architects also discovered the Ancient Skeleton and constructed the Lost River Laboratory Cache around this time.
- The Architects place various relics from other alien races, including humankind, in the Primary Containment Facility.
- After testing the living Sea Emperor Leviathan, the Architects discover she is too old to produce Enzyme 42 potent enough to work as a permanent cure. Instead, the Architects research the unborn eggs on the premise that a younger specimen would produce stronger enzymes. The Sea Emperor Leviathan attempts to telepathically communicate to the Architects that forcefully hatching the eggs would not work, but, according to her, "they could not hear."
- The Architects dissect a Sea Emperor Leviathan egg to study the fetus, but the process killed the fetus. They place a second egg and more eggs from other species on the planet in the Primary Containment Facility's egg lab for further research. The Architects place the remaining five Sea Emperor Leviathan eggs into the Incubator Device.
- The Architects take a Sea Dragon Leviathan egg to the Disease Research Facility to study Leviathan Class egg hatching conditions. The parent Sea Dragon tracks down the egg and rams into the facility, destroying the facility but killing the Sea Dragon shortly afterward. The facility's destruction causes the release of Kharaa on the planet; the Architects subsequently initiate a planetary quarantine, activating the Quarantine Enforcement Platform and ceasing construction of further Warpers.
- Kharaa kills a majority of species on the planet, forcing the ancestors of the modern-day species to rapidly evolve to match the drastic changes in the ecosystem. The Sea Emperor Leviathan species is killed off due to their food source being wiped out by Kharaa, except for the last remaining specimen and her eggs in the Primary Containment Facility.
- The remaining Architects evacuate to the sanctuary caches, disposing of their bodies and uploading their minds to data hubs. It is believed that any remaining Architects who did not upload their minds to caches are killed off by Kharaa.
- The living Sea Emperor Leviathan trains Peepers carrying small amounts of Enzyme 42 to use the Alien Vents and distribute the enzyme around the planet.
Mercury II crash
- Several decades prior to the crash of the Aurora, the Sol Transgov vessel Mercury II is forced down relatively intact by the Quarantine Enforcement Platform, landing in the Arctic Spires.
- The crew makes repairs and attempts to collect biological samples, but is impeded by the ferocious wildlife of Planet 4546B, particularly Ice Worms.
- Kharaa Bacterium-infected crew members are quarantined and left behind with survival gear and supplies. The captain hopes to retrieve them, but is not optimistic.
- On takeoff, the Quarantine Enforcement Platform shoots the Mercury II again, this time scoring a direct hit and breaking it apart. The pieces crash near Delta Island. All survivors are presumed dead within days.
- 10 years prior to the crash of the Aurora, the Quarantine Enforcement Platform shoots down the Degasi which crashes on Planet 4546B.
- The Degasi survivors build their bases on the Floating Island, however, due to heavy 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 that is not recorded in the Databank. 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 and possibly the Floating Island.
- Bart manages to survive for an unspecified amount of time, able to build himself a Seabase and a Seamoth. Although he eventually went back to the Floating Island, where he wrote his final log, and most likely succumbs to Kharaa.
- Marguerit Maida escapes to Sector Zero while the other survivors are presumed dead.
- The Aurora attempts to perform a slingshot maneuver in the atmosphere of Planet 4546B with 157 people aboard to begin the construction of a new phase gate in the Ariadne Arm. Secretly, the Aurora is also tasked with locating the crew of the Degasi, although the crew did not expect to find anything.
- The Quarantine Enforcement Platform detects the Aurora 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 perished during this period of unconsciousness.
(Everything after this may be completed in another order while playing the game.)
- 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.
- After entering the rocket, and activating 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.
- After Ryley returns, Alterra Corporation learns of the value the planet holds.
Xenoworx and Alterra
- Alterra starts funding XenoWorx, supplying with tools, resources, and money; this includes an all-new Alterra PDA.
- XenoWorx is branded as "an Alterra initiative."
Sam and Robin Ayou
- Sam receives a job from Alterra for an extraplanetary mission to 4546B.
- Robin has mixed feelings about Sam's job but congratulates her anyway.
- Sam sends pictures of her base to Robin and keeps in contact with her.
- Robin receives a notice of death from Alterra that states that Sam has died in a tragic accident.
- Robin takes a passenger shuttle from Cal to head to 4546B and find out what happened to Sam.
- Robin's ship is hit by a meteor and crash-lands in Sector Zero of Planet 4546B.
- Robin escapes into the water and finds the Drop Pod that was deployed during descent.
- Robin searches for Sam with the use of the picture Sam sent.
- A voice sends an S.O.S to Robin.
- The voice requires a storage system and refers to Robin's cerebral cortex as a suitable component which Robin misinterprets as her PDA.
- Robin attempts to transfer the voice's consciousness into her PDA, but the voice transfers into her brain.
- Robin's PDA detects a beacon signal on the Delta Island.
- Robin receives a record message from an unidentified woman.
- Robin encounters the woman, and the woman warns Robin to get off her land.
- Marguerit Maida requests that Robin hacks the Communications Tower on the Delta Island.
- Robin inserts a Test Override Module into the mainframe of the tower, causing it to malfunction.
- After Robin hacked the Communications Tower, She receives a call from Marguerit. Robin learns about the location of Marguerit's Greenhouse.
- Robin arrives at Marguerit's Greenhouse, Marguerit is planting Preston's Plant and talking to Robin about her opinions of Alterra and Sam.
- Omega Lab according to the clue of Alterra Facility Map.
- Robin explores Omega Lab and discovers that the Lab was sabotaged.
- Robin arrives at Phi Robotics Center and notes that it was where Sam worked.
- She finds the Spy Pengling lab, Zeta's office, the kitchen, the Administration office, and Sam Ayou's bedroom.
- Robin finds the site of Sam's death, as well as her necklace nearby. She finds the Frozen Leviathan.
- She completes her sister's work and cures it.
- Robin creates Al-An's Storage Medium and the parts to it. Al-An tells robin to go to The Architect Phase Gate Facility.
- Robin arrives at Architect Phase Gate Facility.
- Al-An opens a Phasegate to a unknown location. He tells Robin to finish any remaining business on the planet, and then leaves.
- Robin goes through the phase gate where Al-An is opening a Large Phasegate. He gives Robin a pair of Architect Arms to help align energy masts to build a Architect Ship to fly through the Large Phasegate.
- Al-An builds and teleports to the ship, linking with it. Robin then also teleports on board.
- Al-An starts the ship, and flies through the Phasegate. He and Robin then Fly through a asteroid field, to a Second Phasegate to reach the Homeworld.
- If Ryley disables the Quarantine Enforcement Platform before the Sunbeam arrives, the Sunbeam will survive but cannot approach the planet because of the debris field from the Aurora crash, forcing Ryley to build an escape rocket anyway.
- 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.