Timeline

This is the timeline of the Mass Effect universe.

48000 BC (Approximate)
The Protheans, a galaxy-wide civilization linked by the mass relay network, mysteriously vanish, leaving only ruins behind. Much of the technology in use by younger species, such as humans, is eventually based on their artifacts. Archaeologists believe that they were destroyed in a cataclysm.

1900 BC (Approximate)
Tuchanka, the krogan homeworld, enters the nuclear age. In a global conflict, weapons of mass destruction are released, triggering a nuclear winter. In the resulting devastation, krogan society devolves into a collection of warring clans.

1800 BC (Approximate)
A supernova propels one of the mass relays out of its position. The dense nebula formed by the supernova means the relay's position is effectively lost.

580 BC
After developing faster-than-light spacefaring capabilities based upon Prothean technology, the asari begin to explore the mass relay network, and eventually discover the huge Citadel space station at a hub of many mass relays.

520 BC
The salarians discover the Citadel and open diplomatic relations with the asari.

500 BC
The Citadel Council is formed. The asari and salarians together colonize the Citadel station and establish it as a center of the galactic community, led by the Council. With the participation of the volus, a single galactic currency is eventually established, linking all galactic economies.

This year is also known as 0 GS, the beginning of the Galactic Standard (GS) timeline.

500 BC - 0 AD (Approximate)
The turian Unification War begins.

The Council races begin expanding the galactic community, opening first contact with other spacefaring races and integrating them into the Citadel. This is a period of rapid growth and occasional conflict.

The Rachni Wars
The Citadel Council first encounters the rachni, a species of highly intelligent hive-minded insects. They are discovered when an expedition opens a dormant mass relay to their star systems. The rachni prove to be hostile and begin a war with the rest of the galaxy.

80 - 300 AD (Approximate)
The Rachni Wars continue. The salarians transplant the primitive krogan to another world and manipulate them into acting as soldiers for the Citadel Council; the krogan eradicate the rachni.

300 AD
In gratitude for their aid during the Rachni Wars, the Council grants the krogan a new homeworld. Free of the harsh environment of Tuchanka, the krogan population explodes.

300-600 AD (Approximate)
The krogan begin to expand exponentially, colonizing many new worlds. Growing concerns about their expansion lead to the founding of the Special Tactics and Reconnaissance branch of the Citadel.

The Krogan Rebellions
Krogan warlords leverage veterans of the Rachni Wars to annex territory from others in Citadel space. Eventually the Council demands withdrawal from the asari colony of Lusia, but the krogans refuse. A pre-emptive strike is made on krogan infrastructures by the Council, using the newly-created Spectres. The Krogan Rebellions begin.

First contact is made with the turians. In response to krogan threats, they declare war. After the krogan devastate turian colonies with weapons of mass destruction, the turians respond with a salarian-engineered bioweapon, known as the genophage. The krogan population starts its decline.

800 AD
The Krogan Rebellions end. The turians begin to fill the military and peacekeeping niche left by the decimated krogan.

900 AD
The turians are granted a place on the Citadel Council, and their fleet acts as a galactic peacekeeping force.

The Geth War
The quarians create the geth. The quarians notice geth showing signs of independent thinking, and plan to destroy them before they have chance to become self aware. The geth rebel against their quarian masters and, in the resulting war, reduce the quarians to a species of space faring nomads. Contrary to expectations, the geth do not venture outside the former quarian star systems, instead isolating themselves from the rest of the galaxy behind the Perseus Veil.

1900 AD-2100 AD
The galactic community continues to expand. With the exception of the Geth War, this period is a time of peace and prosperity.

2069 AD
Armstrong Outpost at Shackleton Crater becomes the first human settlement on Luna. It is formally founded on July 24, the 100th anniversary of the first lunar landing.

2077 AD
Liara T'Soni is born to Matriarch Benezia and an unknown asari.

2103 AD
Lowell City in Eos Chasma becomes the first human settlement on Mars.

2137 AD
Ashland Energy Corporation demonstrates helium-3 fuel extraction from the atmosphere of Saturn.

2139 AD
Saren Arterius is born.

2142 AD
Construction of Gagarin Station (Jump Zero) begins beyond the orbit of Pluto.

2148 AD
Humanity discovers a small cache of highly advanced Prothean technology hidden deep beneath the surface of Mars. Building on the remnants of this long extinct race, humans quickly explore the science of mass effect fields, leading to the development of faster than light travel and beginning detailed exploration of the solar system.

2149 AD
Following information from the translated data cache on Mars, humans discover that Charon, Pluto's moon, is actually a massive piece of dormant Prothean technology - a mass relay - encased in ice.

Once activated, Jon Grissom leads the first team of explorers through the relay. They discover that the Charon Relay allows instantaneous travel across thousands of light-years to a synchronized mass relay in another part of the galaxy.

The Systems Alliance charter is signed by the eighteen largest nations on Earth. The Alliance soon becomes the military and exploratory spearhead of humanity.

2151 AD
To defend its rapidly expanding empire, humanity assembles a massive fleet and constructs an enormous military space station at Arcturus, at the nexus of several key mass relays... even though they have yet to encounter another intelligent space-faring species.

An accident at Singapore International Spaceport exposes a human population to element zero.

2152 AD
Roughly 30% of the children born in Singapore after element zero exposure suffer from cancerous growths. Systems Alliance begins settlement of Earth's first extra-solar colony world, the planet Demeter.

2154 AD
Commander Shepard is born.

2155 AD
Saren Arterius is promoted to active service in the turian military at 16.

The Systems Alliance occupies completed portions of Arcturus Station as a headquarters.

The First Contact War
Humanity makes first contact with another space-faring culture: the turians. Unfortunately, the encounter is far from peaceful. The turians find the human fleet attempting to activate a mass relay, something forbidden in galactic law after the Rachni Wars, and attack. Over the next several months, a brief but tense conflict known on Earth as the First Contact War ensues. David Anderson, newly graduated from the Alliance's elite N7 programme, serves with distinction. Saren's brother is one of the turian casualties. Finally General Williams is forced to surrender the garrison at Shanxi to the turians, which is later liberated by the Alliance fleet.

This conflict draws the attention of the Citadel Council. The Council intervenes before hostilities escalate further, revealing the existence of the greater galactic community to humanity and brokering a peace between them and the turians.

2158 AD
Humans learn potential of biotics. An international effort to track element zero exposures begin. Roughly 10% of exposed children show some sign of biotic ability.

2159 AD
Saren becomes the youngest turian to enter the Spectres.

2160 AD
Systems Alliance Parliament formed.

With the existence of human biotics firmly established, the BAaT programme is set up on Gagarin Station to train potential candidates and develop biotic implants. First experimental 'L1' implants used in 2163.

2161 AD
Amid concerns over gene therapy and genetic modifications being misused, the Alliance Parliament passes the Sudham-Wolcott Genetic Heritage Act.

2165 AD
Humanity continues to expand, founding more colonies and establishing trade alliances with many of the other species who recognize the authority of the Citadel Council. In 2165, the Council makes official recognition of humanity's growing power and influence in the galactic community. Humanity is granted an embassy on the Citadel, the political and economic heart of the galaxy. Tensions grow between humans and batarians as they compete for territory in the Skyllian Verge.

The events of Mass Effect: Revelation occur. Saren uses files taken from Dr. Shu Qian and Edan Had'dah to start searching for the artifact they discovered near the Perseus Veil.

2167 AD
L2 biotic implants first developed and used in humans; Kaidan Alenko is among the first to receive the new implants.

2170 AD
The human colony of Mindoir is attacked by batarian slavers. Many colonists are killed or captured. L3 biotic implants are developed after the L2 implants prove to be dangerous.

2174 AD
Ashley Williams finishes high school and enlists in the Alliance military.

2176 AD
Batarian-funded pirates and criminals launch a surprise attack on the human colony of Elysium, later known as the Skyllian Blitz. The assault is repulsed by the Alliance fleet and ground teams.

2177 AD
During a recon mission to find a missing colonial pioneer team on Akuze, a unit of fifty Alliance marines is wiped out by thresher maws.

2178 AD
The Alliance tracks several pirate FTL exit vectors during the 'Theshaca Raids'. In retaliation for the Skyllian Blitz, the Alliance launches a major offensive against the moon of Torfan and destroys the criminal bases there, mostly populated by batarians. After taking heavy losses the batarians withdraw from Citadel space into their home systems.

Tali'Zorah nar Rayya’s mother dies after contracting an airborne virus aboard the Flotilla.

2183 AD
Commander Shepard - now a promising young officer in the human Systems Alliance Military - is assigned to the crew of the prototype SSV Normandy, the most advanced vessel yet designed.

Source: Galactic Codex: Essentials Edition 2183