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A timeline of the Half-Life universe can be made by gathering known dates. Several retcons having been made since the release of the first game, because it is still being written as of today (2019), and because technological limitations have changed in the intervening time, a complete official Half-Life series timeline will probably never be made, since it could probably make the writers contradict themselves and limit their creativity for possible subsequent episodes. Despite that, general events can be organized in a chronological order, around known dates.
- Cave Johnson appears in the UP Pioneer Press headlines for buying a salt mine in Upper Michigan, which is later reconstructed as the Aperture Science Innovators facility.
Between 1944 and 1954
- Richard Keller is born.
- Aperture Science receives the award for Best New Science Company from the Science and Business Institute of America.
- Aperture Science is rated #2 among the Top 100 Applied Science Companies by the Mechanical Engineering World Journal.
It is during this decade that the Black Mesa facilities are probably built, before being purchased and refurbished later by Black Mesa (several Half-Life texture files names contain the word "fifties", suggesting the facility is as old as from the 1950s).
- Aperture Science is the Runner Up for the US Department of Defense's Contractor of the Year award. By now, Aperture Science has begun testing Repulsion Gel.
- Aperture Science is the Runner Up for the US Department of Defense's Contractor of the Year award again.
- Aperture Science receives the Spirit of Idaho National Potato Board award for the promotion of Potato Science.
- The Eisenhower administration signs a contract with Aperture Science to manufacture shower curtains to all branches of the US Military, except the Navy.
- Pump Station Alpha (which pumps Repulsion Gel) is in active use by now.
- Aperture Science is involved in US Senate hearings regarding "missing astronauts". By now, Aperture Science has gone black bankrupt. Cave Johnson says that Black Mesa has stolen and remade many of Aperture's products.
Between 1968 and 1978
- Apollo 11 lands on the Moon.
- Aperture Science re-opens Test Shaft 09 for testing. The lower sections appear to remain unused.
- Aperture constructs Pump Station Beta and begins Propulsion Gel testing.
Between 1972 and 1982
Between 1974 and 1984
- Gina Cross is born. Cite error: Closing </ref> missing for <ref> tag.
- The Conversion Gel Testing Facility is updated with an additional wall.
- Word reaches Aperture Science management that Black Mesa is working on a similar portal technology. In response to this news, Aperture Science begins developing GLaDOS, although the name was already in use in 1982. GLaDOS V.1 is activated, and (for the first time) attempts to kill all the staff of the Aperture Science. 
- This is the most recent date for the Aperture Image Format. At that time, it is maintained by Doug Rattmann.
Sometime in this time period, Cave Johnson dies of moon-rock poisoning. It is unspecified when exactly it happened. The Borealis is claimed lost at sea.
- Judging from Chell's handwriting and spelling skills, she is under the age of ten, meaning that the Aperture Science Bring Your Daughter to Work Day event occurs sometime early in this decade, and ends in an unspecified disaster.
- The Aperture Science Red Phone plan is implemented in case GLaDOS appears to become sentient and godlike, requiring an employee to sit by a red phone on a desk in GLaDOS chamber's entrance hall.
- At this time, GLaDOS's version is 3.11. This is also the latest known date of Aperture Science using a bulletin board system.
- Aperture Science releases several testing elements, such as the Excursion Funnel, a tractor beam-like funnel made of liquid asbestos, the Thermal Discouragement Beam, a laser to be used with a Weighted Pivot Cube to destroy Sentry Guns and activate some buttons, the Aerial Faith Plate, a catapult plate flinging into the air Test Subjects or any other object upon contact, and the Pneumatic Diversity Vent, a variant of the Vital Apparatus Vent used for distributing objects to Test Chambers.
- On an unknown time before GLaDOS' activation, Chell applies to work on Aperture Science as a test subject, but is rejected.
- This is the "year" during which the Black Mesa Incident occurs. Deliberately kept vague by the Half-Life team, it could be any date from 2000 to 2009.
Deduction points at "May 16, 200-" for the precise date of the incident. What follows are the different facts and clues leading to that choice:
- The year "200-", first appearing in the Half-Life instruction manual, is given in every official source from the Half-Life story arc era.
- Several entries from Adrian Shephard's diary are given in the Opposing Force instruction manual, written by Gearbox writers. March is used, corroborating the Raising the Bar date. Shephard says in his last diary entry, written on March 15, "We were told today to be ready in case it happens tomorrow.", suggesting that the incident occurs on March 16. It seems that the Gearbox writers replaced May by March: in the Half-Life instruction manual, Freeman is said to start working at Black Mesa on May 15 (later retconned to an unknown, earlier date), he is also said in the Half-Life PlayStation 2 instruction manual to attend the Hazard Course on May 16 at 7:30 (in a Hazard Course schedule with dates all set in May), and Barney is said to start his duty on May 16 at 9:00. Therefore May 16 appears to be the best day for the incident, and consequently March from Shephard's diary should be replaced by May, for consistency.
- While "200-" could refer to any date from 2000 to 2009, a note by series' writer Marc Laidlaw seen in Raising the Bar features "March 31, 2003", and a time, "4:33 p.m.". Although it has not been confirmed by Valve, it is possible that the Half-Life events originally were to start on March 31, 2003.
- A calendar with the "Blue Marble" photo is also seen in the Half-Life chapter Office Complex, in the Opposing Force chapter Welcome to Black Mesa, in the Blue Shift chapters Insecurity and Captive Freight and in the Decay chapter Domestic Violence, always using the same texture file showing the December page. While the table was not made with much precision, December 1, 8, and 15th start on a Sunday, suggesting the calendar is for the year 2002. However, there should be no reason every visible calendar should be opened to several months after the current date of May 16. One possible explanation for why these calendars are opened to December is that the Black Mesa Incident occurred after 2002, and that the calendars that are seen are actually several months out date, either due to Black Mesa not purchasing new calendars or simply the forgetfulness of staff members.
- Considering that the lack of accurate calendars (as hypothesized in the previous paragraph) likely could not be overlooked for more than a year or two at most, it is quite probable that the Black Mesa incident occurred in 2003. This concurs with Laidlaw's notes, indicating that the most likely date and time of the Black Mesa Incident would be Friday, May 16, 2003, at 8:58 AM UTC-07:00. However, since Valve has not confirmed this date, one should hesitate before treating this time as absolute.
- On March 24, 2010, an updated and expanded Aperture Science timeline originally given on ApertureScience.com in 2006 and submitted by Erik Wolpaw was published on Game Informer. Several dates were changed, and the last paragraph was expanded with facts suggesting that the Black Mesa Incident had occurred in 1998, the same date as that of Half-Life's release, instead of the original "200-". However Marc Laidlaw dismissed "1998" as the date for the Black Mesa Incident, as the date "200-" given when the first Half-Life was released is the only correct one. It is unknown why Erik Wolpaw made that mistake, and if it was intended or not. For convenience and consistency, that "1998" will always be replaced by "200-" on the wiki, even with the dates pertaining to Aperture Science.
Several days before May 16
- GLaDOS is activated as one of the planned activities on Aperture's Bring-Your-Cat-to-Work Day. Upon being activated, she takes control of Aperture Laboratories, locks everyone inside, and kills the Enrichment Center staff with a deadly neurotoxin if they refuse to opt in to her new testing initiative.
- From Shephard's diary entries (originally March; see above): "Another typically hellish day at base camp... I'll be glad when this is over and I can finally can get assigned a mission. There has been this really weird civie spotted at the base. Rumor is he's from some government branch looking to recruit; others say he's with some secret research group. I would jump at the chance to join. It would be cool just for the change and the adventure."
- The original date that Gordon Freeman receives a letter from the Black Mesa Office of the Administrator's LM confirming he is hired. It has now been retconned to an earlier date.
- From Shephard's diary entries (originally March; see above): "I finally saw the government guy today. I am not sure he is a g-man, but he was wearing a really uptight suit and carrying a briefcase. He looked more like a lawyer or insurance agent to me. I did notice him checking me out. Several times throughout the day I spotted him just watching me during training. I wonder what he's up to..."
- From Shephard's diary entries (originally March; see above): "For weeks our drills have been the same crap day after day. Today we assemble for the morning run and our drill instructor tells us we have one week to become experts at indoor strategic combat. We will be spending every day this week at the combat simulation facility. As far as I know this a specialized training not taught in boot camp. What I want to know is if this is to test our ability to adapt or if we are being readied for a specific mission? Time will tell..."
- Colette Green receives a letter from the Black Mesa Office of the Administrator's LM saying that sample GG-3883 will replace sample EP-0021.
Before May 12
- Barney Calhoun is performing a retinal scan and has his salary increased. His two-day Security Guard Training is scheduled.
- From Shephard's diary entries (originally March; see above): "The rumors have been flying since our indoor combat training began. Most of my peers are convinced that we are being primed for a mission. No one can agree on what the mission is. I have heard the name Black Mesa Facility thrown around a lot, but I have no information about the place. The rumors are that some top-secret research is going on there. Doesn't sound too exciting to me..."
- First day of Barney Calhoun's Security Guard Training under Miller's Holographic Instructor counterpart, in Sector A Training Facility. This is the Blue Shift Hazard Course.
- Second day of Barney Calhoun's Security Guard Training.
- Walter Bennet is being instructed by Gina Cross for an Anti-Mass Spectrometer Overload Simulation.
- Colette Green was to be instructed by Isaac Kleiner for an Anomalous Materials Handling, but it was postponed to June.
- Barney Calhoun is assigned to a 09:00 - 22:00 Blue Shift assignment until August 15 and reports at Area 3 Medium Security Facilities at 09:00. Other unknown security guards are assigned to Red, Orange, Yellow, Green and Indigo Shifts in specific areas of Sector A, B, and C. For that timespan, the Violet Shift is on standby.
- From Shephard's diary entries (originally March; see above): "The rumor has been confirmed. We are being trained for a mission at the Black Mesa Facility. All I know is that the place is being used by scientists who are doing some kind of new research. I can't imagine what we would be needed for. We were told today to be ready in case it happens tomorrow. I don't know what "it" is, but the whole thing is a little strange. I kind of hope it doesn't happen; the mission doesn't seem to have much excitement potential. I'd rather hold out for something with more likelihood of combat."
- This day was originally Gordon Freeman's first day of work at Black Mesa, but it was retconned in Half-Life 2 and its episodes, where it is implied that Gordon was already working for some time at Black Mesa before the incident: Barney tells Gordon he owes him a beer and reminds him who he is when first meeting in the City 17 Trainstation, and Alyx tells in the City 17 Underground that Gordon and Barney would compete in air ducts to get into Kleiner's office whenever he got himself locked out, among others.
- Adrian Shepard is "mysteriously" bumped up to the advanced training list. This is also the point in time when G-man visits the Marine Boot Camp.
- This was the original date for Gordon Freeman's HEV Suit Training in Sector A. It has now been retconned to an earlier date.
- Several system crashes occur around Black Mesa (the security guard in the Sector C lobby states he has had a system crash "about 20 minutes ago").
- Barney Calhoun starts his tram ride from the Area 8 Topside Dormitories at Black Mesa, to start his second day at Area 3 Medium Security Facilities in Sector C. He arrives there as soon as Gordon Freeman begins his tram ride, at 8:47.
- Gordon Freeman starts his tram ride from Level 3 Dormitories at Black Mesa. He is 30 minutes late.
- The Black Mesa Incident. Freeman conducts an experiment on sample GG-3883 in Sector C's Anti-Mass Spectrometer. The experiment goes wrong and triggers a Resonance Cascade, teleporting Xen creatures to Earth.
Remainder of the day
- Freeman, Calhoun, Green and Cross fight their way through the facility.
- Overnight, Freeman successfully launches the rocket.
- Adrian Shephard and his squad are attacked by Alien Aircraft and their Osprey crashes.
- As heard during the tram ride at the start of Half-Life, the Black Mesa Hazard Course Decathlon was to start in the Level 3 facility. This never happened due to the incident.
- Early in the morning, Gina Cross and Colette Green are able to perform a resonance reversal. Their fate, along with Keller's, are unknown.
- Barney Calhoun successfully escapes Black Mesa with Rosenberg, Simmons and Walter Bennet.
- As Gordon Freeman fights his way across the surface towards the Lambda Complex, Shephard is left behind (this matches the message addressed to Cooper). Race X creatures appear sometime later.
- Black Mesa is destroyed by an atomic bomb. Shephard is also placed in stasis by the G-Man.
- As the Black Mesa facility is destroyed, GLaDOS's race against Black Mesa is stopped.
- Colette Green was to conduct a Public Relations Tour. This never happened due to the incident.
- Otis Laurey was to be instructed by the Miller's holographic instructor counterpart for a Security Guard Training, but he apparently postponed and Cross suggests to Green to ask Barney to replace him. This never happened due to the incident.
- Barney Calhoun's Blue Shift was to end on that day. It ended earlier due to the incident.
After May 200-
- During this period of almost 20 years Gordon Freeman is in stasis. It starts at the aftermath of the Black Mesa Incident in May 200- and ends at Gordon's arrival in City 17 in 202-.
- Portal Storms rage on Earth while Xen creatures continue to be teleported. The governments and United Nations provide the protection centers located in major cities worldwide.
- The Aperture Laboratories are in a lockdown, with employees still trapped inside. The number of Aperture Science employees also likely diminishes, until there are only a few of them left.
- The Combine launches an assault on Earth. Earth governments and the United Nations enter into war against them. The Seven Hour War occurs. Finally, Earth surrenders to the Combine and Wallace Breen, former Black Mesa Administrator, is appointed Earth Administrator. Meanwhile, the Combine activate a suppression field that prevents child birth.
- This is the period during which Portal is set. It occurs a short amount of time after the Combine invasion of Earth.
- In the Aperture Science computer-aided Enrichment Center, Chell is awoken by GLaDOS who makes her perform seemingly routine tests. However Chell soon learns that the Aperture employees are long dead or escaped, and that GLaDOS is seemingly the only being left in the decaying facility. After much promise of cake at the test's conclusion, Chell is met with an incinerator, which she narrowly escapes, and works her way through the maintenance areas, despite GLaDOS's protests. Eventually, Chell finds GLaDOS's control room, and manages to escape death by neurotoxin by detaching the GLaDOS's Personality Cores, and partially destroying her as a result. Chell is forced to the surface by GLaDOS's explosion, only to be dragged away from freedom and back into the facility by the Party Escort Bot. Unknown to Chell however, GLaDOS is still alive.
- Doug Rattmann, being the one of the last Aperture employees alive, witnesses GLaDOS' destruction. After the Party Escort Bot drags Chell back into the facility, Rattmann feels guilty for Chell's situation and reenters the facility to help her.
- At an unknown time before Gordon Freeman's awakening, Isaac Kleiner and Eli Vance each build in their respective labs a teleport not needing a Xen relay with the aid of Alyx Vance and Judith Mossman, among others. When tested on a cat, it kills it, traumatizing Barney Calhoun in the process. They then continue working on it until Freeman's arrival.
Between 2014 and 2028
- This is the last time Alyx Vance drives Highway 17, as said by her in the radio transmission at Shorepoint Base.
Between 2015 and 2029
Day 1 of Gordon's journey
- Under two decades after the Black Mesa Incident, Gordon Freeman is awakened by the G-Man after a long period of stasis, he is placed on a train entering the City 17 Trainstation.
- Barney prevents Gordon from entering a prisoner train and reintroduces both himself and Dr. Kleiner to Gordon.
- Breen's speech on instinct occurs at this time.
- Gordon explores City 17. During the exploration, he is ambushed by several Civil Protection units for entering a residential building. Gordon is saved by Alyx, who brings him to Kleiner's Lab.
- Alyx is teleported to Black Mesa East, but a teleporter accident causes Lamarr to be sent to the Wasteland and Gordon to ultimately be teleported a short distance outside the lab.
- The teleporter accident causes the Combine to send CP officers to kill Gordon.
- Gordon leaves City 17 with an airboat, and the Underground Railroad is dismantled by Civil Protection. Station 6 and 7 are destroyed by Headcrab Shells.
- Gordon attacks the APC garage and Gate 5, killing all Combine forces within. Breen's speech on Gordon Freeman occurs as Gordon raids the APC garage.
- Gordon destroys a Hunter-Chopper shortly before entering Black Mesa East.
- As Gordon enters Black Mesa East, he disembarks the airboat and meets Judith Mossman.
- Gordon is given the Gravity Gun by Alyx.
- Combine forces led by Breen raid Black Mesa East while Alyx, Dog, and Gordon are in the nearby scrapyard. Gordon escapes the raid and enters the nearby town of Ravenholm. Eli is captured and taken to Nova Prospekt. Judith Mossman is also taken however has not been captured by the Combine. Dog and Alyx also escape the raid.
- Gordon meets Grigori, Ravenholm's priest. Gordon uses Grigori's traps to explore the town.
Day 2 of Gordon's journey
- Grigori helps Gordon escape Ravenholm.
- After navigating an underground mine, Gordon fights several Overwatch soldiers attacking Shorepoint Base.
- Alyx tells Gordon that Eli has been captured, and that she will infiltrate Nova Prospekt by train.
- Gordon leaves Shorepoint Base with the Scout Car.
- By this time Dock 137 and Bridge Point have been occupied by the Combine. The Combine has also taken a Petroleum Station on the Coast.
- Gordon visits New Little Odessa. He helps Colonel Odessa Cubbage destroy a Combine Gunship while the Colonel contacts Lighthouse Point. After successfully destroying the gunship, Gordon continues his journey to Nova Prospekt.
- Gordon clears out the Combine presence at Dock 137, the Petroleum Station, and Bridge Point.
- Gordon reaches Lighthouse Point, where he helps the Resistance members there repel a Combine attack. Shortly after leaving on foot, Lighthouse Point is again attacked by Combine. The Scout Car is captured, and the base is presumably occupied by the Combine.
- After traversing the Antlion territory and killing an Antlion Guard, Gordon receives Pheropods and enters the Vortigaunt Camp. After a brief tutorial on pheropod use, Gordon leaves the camp to Nova Prospekt.
- Gordon uses antlions to attack the Combine in the prison. Breen gives another speech specific to Overwatch soldiers, expressing the advisors' disappointment in their failure to stop Gordon.
Day 3 of Gordon's journey
- Gordon meets Alyx in the Depot. The two send Eli to the transportation room and uncover Mossman's cooperation with the Combine.
- Mossman and Eli leave Nova Prospekt to the Citadel with the Combine teleporter.
- Alyx and Gordon leave Nova Prospekt in the Combine teleporter, destroying Nova Prospekt in the process.
- After using the Nova Prospekt teleporter, it takes Gordon and Alyx a week to arrive to Kleiner's teleporter; however, from their perspective it was only a few seconds. During this week the following events take place.
- Lamarr is recovered and returned to Dr. Kleiner.
- The original door to Kleiner's lab is replaced with a much larger door.
- Dog enters and stays inside Kleiner's lab.
- The Uprising of City 17 begins due to the destruction of Nova Prospekt. City 17 citizens are given guns and medical equipment by Resistance members outside the city.
- Headcrab shelling causes many areas of City 17 to be infested by Xenian fauna.
- The City 17 Trainstation is decommissioned and a barrier is placed in front of the entrance.
- Alyx and Gordon reappear in Kleiner's Lab and are briefed by Dr. Kleiner on current events.
- Gordon and Dog leave to find Barney.
- Breen's speech on collaboration occurs.
- Kleiner escapes City 17 with Alyx's help.
- Alyx and Gordon destroy a Combine Power Generator shortly before she is captured by the Combine.
- Gordon finds Barney and the two attack the Overwatch Nexus.
- Breen uses his Breencasts to directly speak with Gordon.
- The suppression device within the Nexus is destroyed, causing the Nexus to be occupied by resistance forces.
- Several Striders are dispatched to retake the Nexus, and attack the occupying Resistance forces.
- Gordon evades and destroys the striders surrounding the Citadel, and is given access to the Citadel itself by Dog.
- Gordon enters the Citadel and loses all his weapons except the Gravity Gun. The Gravity Gun becomes significantly more powerful, allowing Gordon to continue within the Citadel.
- Gordon is briefly captured; he, Eli and Alyx are freed by Mossman after a conversation with Breen.
- Gordon and Alyx prevent Breen from escaping by destroying the Dark Fusion Reactor, causing a massive explosion at the top of the Citadel.
- Gordon is taken into stasis by the G-Man.
Day 4 of Gordon's journey
- The vortigaunts remove Gordon from stasis and place him "a few days" later at the base of the Citadel. During his absence the following events take place.
- The vortigaunts remove Alyx from the Citadel's Dark Fusion Reactor explosion.
- Mossman leaves for a Resistance base in the polar regions.
- Mossman reports that she has discovered the Borealis. The Combine attack her Resistance base during the report.
- Alyx searches for Gordon in City 17's rubble.
- The Combine stores Mossman's report in the Citadel.
- Alyx and Dog discover Gordon at the base of the Citadel. They are told by Eli and Kleiner that the Citadel Core is extremely unstable.
- Alyx and Gordon stabilize the Citadel Core and leave in a stalker train.
- The train is derailed, and both Gordon and Alyx are knocked unconscious.
- City 17's defenses against antlions and Xenian life fail by this time.
- Gordon and Alyx fight through an underground parking lot and escape to the surface.
- Gordon and Alyx meet Barney; Gordon and Alyx agree to create a diversion for Barney so he can move citizens to the Technical Trainstation.
- Gordon and Alyx fight through a hospital.
- Gordon, Alyx and Barney successfully get to the train station.
- Barney and the surviving citizens leave City 17 first. A Strider appears, and it is destroyed by Gordon. Gordon and Alyx leave City 17 on the last train.
- City 17 is destroyed when the Citadel explodes due to the Combine's request for reinforcements.
- The Superportal is formed. Portal Storms emit from the City 17 ruins.
- Alyx is impaled by a Hunter. The Victory Mine Vortigaunt stabilizes her.
- Gordon and the Victory Mine Vortigaunt meet Griggs and Sheckley in a resistance outpost. Gordon defends against an antlion assault on the outpost.
- Gordon and the Victory Mine Vortigaunt evade the Antlion Guardian and retrieve the antlion extract to heal Alyx.
- The G-man takes the opportunity (while the vortigaunts are preoccupied healing Alyx) to have a "heart to heart" with Gordon and tells Alyx to relay a message to her father.
- Alyx is healed, and the two leave Victory Mine.
- Alyx and Gordon fail to kill a Combine Advisor.
- Alyx and Gordon see Dog as they approach White Forest and race him to the entrance.
- Mossman's report is inspected at White Forest.
- White Forest is attacked by the Combine, but the attack is repelled.
- The Superportal is destroyed.
- Eli is killed by an attack from two Advisors.
- GLaDOS' partial destruction is followed by a period of inactivity within the Aperture Laboratories, during which time maintenance systems and Personality Cores maintain their functions. The facility remains in disarray, having become overgrown and dilapidated. Pre-recorded 'Emergency Test Protocols' can oversee test chambers in times of cataclysmic system failure, "able to sustain themselves on a minimum 1.1 Volts". Chell spends this time in stasis until the events of Portal 2. For at least some of her stasis, Chell is under supervision by a remaining Aperture employee, Doug Rattmann.
- Chell is reawakened by Wheatley, a personality core. Wheatley insists he can secure an escape route out of the dilapidated Aperture Laboratories, which instead results in the inadvertent reactivation of GLaDOS. As the story progresses, GLaDOS repairs most of the facility as evidenced by the steadily improving conditions of the testing courses that Chell is forced to complete.
- Wheatley rescues Chell from the testing courses and helps her to GLaDOS's control room, sabotaging GLaDOS's defenses along the way.
- GLaDOS's begins the Aperture Science Cooperative Testing Initiative.
- After an extremely brief confrontation, Wheatley, with Chell's help, is placed in control of the Aperture Science facilities. He immediately becomes mad with power and proceeds to integrate GLaDOS's core with a potato battery. Lashing out, he sends Chell and GLaDOS's potato down an elevator shaft several kilometers deep.
- Chell survives the fall because of her Long Fall Boots and GLaDOS survives because of her happenstantial situation as a potato; she is, however, carried off by a crow at this point. Chell now finds herself traversing a series of old condemned Enrichment Spheres, the precursor to the testing rooms that GLaDOS employs in the new Aperture facilities. The first of these spheres were built at the time of Aperture Science's foundation, earlier than June 15, 1961, at which time Aperture Laboratories was under the direction of Cave Johnson. They continued to be used at least until Johnson's death by poisonous moon-rock some time in the late 1980s.
- Chell eventually finds GLaDOS, makes her way back to the facilities controlled by Wheatley, and finds that Wheatley has managed to inadvertently demolish massive portions of the facility. Signs of the extent of the facility's degeneration include the announcer which directed Chell's testing before GLaDOS's reactivation repeatedly interrupting Wheatley with warnings of the facility's imminent destruction. Eventually, Chell manages to make her way back to Wheatley's "lair" and after a relatively brief battle, puts GLaDOS back in charge. As a token of appreciation (or perhaps of resignation), GLaDOS allows Chell to leave Aperture Science, and sends her back to the surface. The game ends with the player viewing a seemingly endless field of grain, before the view is interrupted by the Companion Cube from the first Portal game being sent up after Chell.
- Because the exact amount of time that passed between Portal and Portal 2 is unknown, it is also unknown whether the Combine is still in control of Earth, or what became of Chell following her escape from Aperture Laboratories.
- ↑ Marc Laidlaw Vault on the HalfLife2.net Forums
- ↑ 2.0 2.1 ApertureScience.com
- ↑ Cite error: Invalid
<ref>tag; no text was provided for refs named
- ↑ 4.0 4.1 4.2 4.3 Portal ARG
- ↑ Chell's Bring Your Daughter Work Day poster
- ↑ Portal 2, chapter The Escape
- ↑ Portal commentary
- ↑ 8.0 8.1 8.2 Game Informer, April 2010 issue
- ↑ Portal 2 Demo (Part 2) - E3 2010 on IGN's YouTube channel
- ↑ Portal 2 Demo (Part 3) - E3 2010 on IGN's YouTube channel
- ↑ Portal 2: Lab Rat
- ↑ 12.0 12.1 Facts about the date issue on the Marc Laidlaw Vault on the HalfLife2.net Forums
- ↑ Half-Life 2: Raising the Bar
- ↑ 14.0 14.1 14.2 14.3 14.4 Half-Life: Opposing Force instruction manual
- ↑ 15.0 15.1 15.2 15.3 15.4 15.5 15.6 15.7 15.8 Half-Life PlayStation 2 instruction manual
- ↑ 16.0 16.1 16.2 16.3 16.4 16.5 Marc Laidlaw
- ↑ 17.0 17.1 17.2 17.3 17.4 Half-Life: Blue Shift instruction manual
- ↑ 18.0 18.1 18.2 Half-Life: Blue Shift
- ↑ Stephen Bahl as quoted on Marc Laidlaw Vault on the HalfLife2.net Forums
- ↑ 20.0 20.1
- ↑ The Final Hours of Portal 2
- ↑ "Valve Plans To Bridge Portal And Portal 2 With A Surprise, Keep Gordon Freeman Out Of It" on Kotaku.com
- ↑ The Marc Laidlaw Vault on Steam Users' Forums
|Game storyline articles|
|Half-Life story arc||Half-Life storyline · Half-Life: Opposing Force storyline · Half-Life: Blue Shift storyline · Half-Life: Decay storyline|
|Half-Life 2 story arc||Half-Life 2 original storyline · Half-Life 2 storyline · Half-Life 2: Episode One storyline · Half-Life 2: Episode Two storyline · Portal storyline · Portal 2 storyline|
|Overall||Timeline of the Half-Life universe|