This is an improved and more accurate version of the Sonic Events Timeline I made on Chao Island in 2011.
Certain adaptations of the Sonic universe, like the Archie continuity and Sonic X have provided dates for events in their storylines, usually setting the stories in the far future. However the video game continuity has not done this, and constructing a timeline of events in that universe requires looking for clues to pinpoint the relevant dates.
There are a number of details that tell us what the chronology of the SEGA Sonic world is like. It is broadly similar to the contemporary real world; there are analogues of real world locations like the United Federation paralleling the USA; there are real world cultures and religions like Islam and Christianity, which have existed long enough and in similar enough circumstances to produce counterparts to real world works of literature like The 1001 Nights and the Legend of King Arthur. We would conclude therefore that the inhabitants of the United Federation use the same twelve month calendar and AD/Common Era dating system as we use, they observe the same holidays (Tails celebrates Christmas
), etc. This means we can reasonably use the same kinds of assumptions for dating events in the Sonic universe as we would use for dating real world events.
Sonic's world also possesses numerous technologies that resemble real world developments- however, in many cases technology on Sonic's world is far more advanced and futuristic than it is in the real world. This last point makes relating events in Sonic's history to our own history difficult.
However, there are two technologies in the Sonic-verse that appear to have developed at the same pace as their real life counterparts- we would not suppose that a world more scientifically advanced than ours' would produce these inventions later than we did- which makes it possible to precisely date a pivotal event in that world's history.
The first one is sepia photography.
Despite the incredible scientific breakthroughs made aboard the Space Colony ARK, Gerald Robotnik was still making sepia and monochrome photos of himself and his granddaughter. The photo of the Biolizard in the Project: Shadow report was also in black and white.
http://info.sonicretro.org/images/8/8a/ ... file_2.png
In the real world, color photo cameras first began to be marketed by Polaroid in 1963
, which would indicate that Project: Shadow began no later than that time. Too much later, and one would assume they would have switched to color film, as Prison Island was evidently using when they executed the Professor.
Which takes us to the second real world technology, sattelite television broadcasting.
Throughout SA2 Eggman transmits his doomsday ultimatums from the Space Colony ARK, as is his grandfather's final message in the Last Story. Eggman and Tails also watch an ordinary sattelite tv broadcast from DreamNEWS reporting on Shadow's acts of terrorism, confirming these are the same kinds of communication they use in everyday life. The first real world television transmission sattelite was put in orbit in 1963
. This would mean that GUN's raid on the Space Colony happened after that point; any earlier Gerald would not have been able to plan transmitting his final message to the Earth from the sattelite.
This information allows us to comfortably place the beginning of Project: Shadow and the creation of the Biolizard in 1963. Project Shadow gave its 23rd report on the progress of the Biolizard on January 27th; if these reports were made daily that would mean Project Shadow began on January 4th. We know the raid on the ARK happened 50 years before SA2, and from Rouge's report that Gerald was approached by the president to research immortality 52 years before SA2: It was a letter addressed to Professor Gerald from the President of its time, 13 Presidents ago, confidentially requesting him some new research. The subject of the letter is as follows: "Mankind's ultimate eternal dream, researching for immortality."
Assuming a four year term of office, 13 presidents is 52 years. This gives Project: Shadow a duration of two years, and would place the creation of Shadow the Hedgehog and the raid on the Space Colony ARK in 1965.
Sonic Adventure 2 therefore must occur 50 years after 1965, in 2015. Unusual timing given it's release date, but consistent with the evidence.
We know enough time passed between SA and SA2 for newspapers to report on the events of the first game
, and these papers were still considered recent. This would imply less than a month passed between SA and SA2. According to NPC dialogue ("I feel great! There's nothing like swimming pools and the ocean in the summer!"
), Sonic Adventure takes place in the summer. Sonic's trip to Station Square for a beach vacation would imply the events take place fairly early in the summer, which is supported by dialogue from other NPCs indicating vacationers are just beginning to arrive in the city. The first day of summer in 2015 was June 21st, meaning Sonic Adventure must take place in late June, while Sonic Adventure 2 would be set in July. Interestingly, since Sonic Adventure was when the characters' ages were definitively established, this would support the conventional wisdom that Sonic celebrates his birthday on June 23rd.
On that note, in Sonic Adventure Amy was 12 years old, while her age was given as eight in Sonic CD
, which would mean that CD takes place four years before Sonic Adventure. Now, some would argue that Amy's age was simply retconned, and there's no other indication that a significant amount of time passed between CD and SA. However, they have forgotten that the Little Planet only appears for one month each year
, which means games like Sonic 4 Episode Metal and Sonic Mania that are set between CD and SA must occur at least a year apart; this argues in favor of the time gap we would surmise based on Amy's age.
Is it possible to determine what month of the year the Little Planet appears in? In Sonic 4 Episode II the White Park Zone is decorated with Christmas lights, indicating the Little Planet appears in December.
This would mean Sonic CD takes place in December of 2011. Now Sonic CD was released after Sonic 2, but it must occur before Sonic 2, because otherwise it would mean Tails was 4 years old in his first appearance. Such a young age seems improbable for a number of reasons. Since Sonic Adventure occurs in June 2015, the latest point Sonic Mania can take place is December 2014, and the latest Sonic 4 Episode Metal can take place is December 2013. Since Sonic 4 is supposed to occur just after the events of S3&K (and thus Sonic 2), that would place the Death Egg saga in 2013. That would make Tails six years old in his earliest appearances, the same age as Cream and Charmy in Sonic Heroes.
Since Sega Sonic Arcade was also released in the gap between Sonic 2 and Sonic 3, and like Sonic CD it doesn't feature Tails, we can reasonably assume it also takes place before Sonic 2. Likewise if Sonic CD takes place in 2011, that would push both versions of Sonic 1 to 2011 as well.
Even though I've acknowledged Amy and Tails aging prior to Sonic Adventure, as in these two cases it's corroborated by the nature of the Little Planet's annual appearance, the same logic doesn't quite work in other cases. For example, no one seems to have aged after Sonic Adventure; despite Sonic celebrating his birthday in Sonic Generations, his official age stayed 15. Indeed, Sonic seems to have "always" been 15.
All other dates can be easily extrapolated from the above fixed points in time using character ages and official statements about the passage of time in-universe. Some, such as the huge time spans between events in the ancient past, are necessarily speculative and only listed to give a general idea of what order they occurred in.
~8000 BC- Dark Gaia awakening. Construction of Gaia Temples.
~3000 BC- Astral Babylon arrives on Earth. Gigan Device constructed.
~2675 BC- Stolen becomes leader of the Babylon Rogues. He invents the Magic Carpet.
~2600s BC- Babylon Garden falls into the desert of Monopole and the Babylon Rogues are scattered.
~2000s BC- Echidna empires expand and build a variety of structures throughout the world. A strained peace between the Echidna clans is established.
2036 BC- Birth of Pachacamac.
1998 BC- Birth of Tikal.
~1980s BC- Knuckles Clan/Nocturnus war.
1984 BC- Destruction of the Knuckles Clan by Perfect Chaos and formation of Angel Island.
1981 BC- Creation of Emerl. Argus Event.
15- Glyphic Canyon transported to Earth by the Black Arms.
980- Birth of Master Zik, founder of the Deadly Six. 
~1811- Eggman arrives from the future to seed the Little Planet with badnik generators; Sonic arrives as well to cleanse the past of his influence.
1868- Birth of Zavok, Master Zik's eventual successor as leader of the Deadly Six.
1883- Birth of Zomom.
1889- Birth of Zazz.
1896- Birth of Zeena.
1904- Birth of Zor.
1953- Birth of Maria Robotnik.
January 4, 1963- Project Shadow begins.
January 27, 1963- Biolizard is created on the Space Colony ARK.
October 1965- Shadow the Hedgehog is created. The ARK raid takes place.
1995- Birth of Vector the Crocodile.
1996- Birth of Storm the Albatross.
1997- Birth of Rouge the Bat. Birth of Big the Cat. Birth of Wave the Swallow.
1998- Birth of Mighty the Armadillo.
Feburary 2, 1999- Birth of Knuckles the Echidna on Angel Island.
1999- Birth of Espio the Chameleon. Birth of Princess Elise III to the Duke of Soleanna.
June 23, 2000- Sonic is born on Christmas Island (perhaps).
2001- Birth of Blaze the Cat. Birth of Jet the Hawk.
2003- Birth of Amy Rose.
2006- Project Solaris fails. "Past" portions of Sonic 06 take place before being erased from history.
2007- Birth of Miles Prower on Cocoa Island.
2009- Birth of Charmy Bee. Birth of Cream the Rabbit.
2011- Events of Sonic 1 and Sonic 1 (Game Gear).
December 2011- Events of Sonic CD.
2012- Events of SegaSonic Arcade.
2013- Events of Tails Adventure, Sonic 2, Sonic 3 & Knuckles, Sonic 4 Episode I, Tails Sky Patrol and Sonic 2 (Game Gear).
December 2013- Events of Sonic 4 Episode Metal and Sonic 4 Episode II
2014- Events of Knuckles' Chaotix, Sonic Chaos, Sonic Triple Trouble and Sonic the Fighters.
December 2014- Events of Sonic Mania
January 2015- Events of Sonic 3D Blast: Flicky's Island and Sonic R.
June 2015- Events of Sonic Adventure and Sonic Shuffle
July 1st to July 3rd 2015- Sonic Adventure 2 takes place
July 31st to August 2nd 2015- Sonic Advance takes place 
August 2015- Sonic Advance 2 takes place
September 27th to September 30th 2015- Events of Sonic Heroes
October 2015- Sonic Pinball Party takes place
October 27th to October 30th 2015- Shadow the Hedgehog takes place
November 2015- Sonic Battle takes place
December 2015- Sonic Advance 3 and Sonic Rush take place
Early 2016- Events of Sonic Riders, Sonic 06, Sonic Rivals, Sonic Rush Adventure, Sonic Rivals 2, Sonic and the Secret Rings, Sonic Riders: Zero Gravity, Sonic Unleashed/Night of the Werehog, Sonic and the Black Knight, Sonic Free Riders, and Sonic Colors/Sonic Colors DS.
June 23, 2016- Events of Sonic Generations.
June 24 to June 30, 2016- Events of Sonic: Lost World. Events of Sonic Forces: Rise of Infinite. Shadow defeats the Jackal Squad while infiltrating one of Eggman's bases.
July 2016- Events of Sonic Forces: Moment of Truth, Sonic Forces: Stress Test, and Sonic Forces: Looming Shadow. Events of Sonic Forces: Episode Shadow. 
December 2016- Events of Sonic Forces.
2018- Events of Sonic Chronicles: The Dark Brotherhood.
2202- Birth of Silver the Hedgehog.
~2211- Sonic and Eggman fight in the Little Planet's Bad Future.
2216- Silver and Eggman Nega begin traveling to the past for various reasons as their histories change. "Future" portions of Sonic 06 take place before being erased from history.
1- "These ancient documents are known as the Gaia Manuscripts. They tell the legend of a disaster that befell our planet some tens of thousands of years ago."
; for my reasoning on the dating of the Babylonians' arrival see here
3- Stolen was the thirteenth leader of the Babylon Rogues, meaning there were twelve preceeding generations before they invented Extreme Gear. Assuming each generation was an average of 25 years long that would give us around 325 years from the Babylonians arrival to the creation of the Magic Carpet. These numbers are only loose approximations.
4- Sonic Chronicles: The Dark Brotherhood (Nintendo DS) United States instruction booklet, pg. 4. "4,000 years ago, the two rival clans of the planet's dominant Echidnas race had been blessed with centuries of peace, albeit strained, but such days were to be short-lived. The expanding borders of the Knuckles' Clan empire and the Nocturnus Clan empire were pushing against each other, and neither side was intent on yielding." Those centuries of peace came before war broke out between them 4000 years ago.
5- Pachacamac's age is given as 52 in Sonic Adventure Navigation Guide
; other character ages also taken from Sonic Channel.
7- Sonic Adventure - A Heavenly Island - 2 - Sonic Jam
, Sonic Chronicles: The Dark Brotherhood Codex Transcript for DS by Platinum Sonic 10 - GameFAQs
Sources from when Sonic Adventure came out give approximate timespans like "more than 3000 years ago", "about 3000 years ago", which doesn't contradict later games like Sonic Battle giving longer approximate timespans, since neither are trying to be precise. As it currently stands, Emerl's profile on Sonic Channel still says 4000 years, while the profiles for Tikal and Chaos don't give a figure for their time period, so my assumption is that SEGA considers 4000 years to be the most correct timescale.
8- - Sonic Chronicles: The Dark Brotherhood Codex, "The Nocturnus historian Nestor the Wise claims that Emerl was "our finest creation". According to Nestor, Emerl didn't destroy the Nocturnus Clan directly, but his creation led to the Clan's disappearance. Emerl and the Gizoids made the Nocturnus Clan unstoppable, and at the peak of their power, they were whisked away to the Twilight Cage.
The "Argus Event" is the name given to the mysterious disappearance of the Nocturnus Clan and their appearance in the Twilight Cage. It was coined by a Nocturnus historian named Nestor the Wise soon after the Nocturnus arrived in the Twilight Cage. The term refers to a strange phenomenon that all Nocturnus echidnas experienced when they first arrived. At the moment the Nocturnus disappeared, all members of the Nocturnus Clan heard a voice in their minds say something that like "Argus." No one has yet been able to explain what this meant."
10- https://info.sonicretro.org/images/3/39 ... rofile.jpg
11- I've previously argued that the past and future eras of the Little Planet are separated from the present by about 200 years, based on the deterioration of Eggman's robots in Sonic CD when compared to Omega being able to remain operational for 200 years in Sonic 06.
12- https://info.sonicretro.org/images/6/61 ... rofile.jpg
13- https://info.sonicretro.org/images/c/cc ... rofile.jpg
14- https://info.sonicretro.org/images/6/67 ... rofile.jpg
15- https://info.sonicretro.org/images/b/b1 ... rofile.jpg
16- https://info.sonicretro.org/images/1/19 ... rofile.jpg
17- https://i.pinimg.com/originals/44/0c/85 ... 66db37.jpg
18- Chaotix Character Profiles - Sonic Jam
19- Sonic Next Gen Production Script.
20- Early materials give Sonic's birthplace as Christmas Island; Sonic the Hedgehog - STI Technical Files - Sonic Jam
21- "It seems we must see what took place 10 years ago."
22- "This is a story from before Tails met Sonic..."
23- Since Sonic 4 depicts Metal Sonic leaving the Little Planet for the first time, those episodes must take place before his appearance in other classic era games like Chaotix and Triple Trouble.
24- "A few months have passed since the events that have caused the island to be skimming on the ocean's surface."
25- Since Sonic Mania features the Little Planet, it must occur one full year after the Little Planet's last appearance in Sonic 4 Episode II; additionally, since Mania features cameos of characters from Sonic the Fighters it presumably takes place after that game.
26- In Sonic Jam Knuckles' age is given as 15 while Tails' is given as 8.
This is plausible if Tails turned 8 just before Knuckles turned 16, and the Saturn era games take place early in the year Sonic Adventure happens. If we followed the logic that Knuckles' birthday is February 2nd, this would place the Saturn titles in January. Note that how the characters react to seeing each other in Sonic Adventure seems to support the idea that a long time has passed since their last encounter.
27- The full moon in the final cutscene of Sonic Advance places this game a month after SA2, which also featured a full moon. They cannot share the same full moon as two nights passed over the course of SA2 (the night of Sonic's arrest and the night of the Eclipse Cannon test shot) and two to three nights passed over the course of Sonic Advance (Secret Base, Casino Paradise, and the final cutscene), and a single full moon is only visible for around three days. In July 2015 the moon was full on July 1st and again on July 31st. I will not address here how the Moon continued to appear full in subsequent games after Eggman exploded half of it...
28- Sonic Heroes manual page 10, "Amy, crazily in love with Sonic as always, is concerned that she hasn't had any contact for over a month." The full moon seen in Hang Castle (if it is a real moon and not some ghost thing) would place this game around September 27th to September 30th.
29- Shadow and Metal Sonic's names on the pinball tournament list indicate this game takes place after Sonic Heroes.
Since Heroes occurs at the very end of September Pinball Party must occur in October.
30- Yet another full moon in the cutscenes, suggesting Shadow the Hedgehog occurs a month after Heroes. They can't share the same full moon as Heroes takes place over the course of three days.
31- Sonic Battle was released before Heroes but obviously takes place after Shadow has regained his memories. Since Shadow the Hedgehog occurs in the last days of October Sonic Battle must occur in November.
32- A large moon like object looms in the background of the Chaos Angel Zone
, which given it's close proximity to the Earth and the presence of a normal sized moon next to it, might well be the Little Planet. If so Sonic Advance 3 would take place in December.
33- At this point following the lunar phases becomes less useful, as there were six full moons between January 23rd and June 20th 2016, and only four games that featured full moons (plus a rare gibbous moon in Sonic Colors). Thus Sonic Riders could occur at the earliest in January, but it could just as easily take place in February and there would still be chances for further full moons. Additionally, the events of Sonic 06 being erased from history mean that the usual caveat about games not sharing full moons wouldn't apply, as the events of one of the other games could conceivably occur before the full moon seen during the Festival of the Sun waned. Further complicating things in this period is that Secret Rings, Rush Adventures, and Black Knight have Sonic traveling to parallel universes, where we're left without any information about the passage of time in Sonic's world between these adventures. Other than release order there isn't as much to go for this part of the timeline.
34- Since Sonic celebrates his birthday in Generations, we would assume it takes place at least a full year after SA where the characters' modern ages were introduced.
35- "A couple of months ago..."
36- "It was one month before the Doctor took over the world."
37-"We've been waiting for a miracle these past six months"
38- Chronicles takes place two years after Eggman's previous defeat.
39-"Approximately 200 years"