Timeline

The Engineer on primordial Earth

4 billion - 2 million BC – The Engineers visit Earth, leaving one of their kind behind. After he drinks black goo, his body breaks down, so that his DNA can recombine to create life.

35,000 BC – Evidence of the Engineers in Scotland.

3590 BC – Sumerian evidence of Engineers' visit to Earth.

2470 BC – Egyptian evidence of Engineers' visit to Earth.

1540 BC – Babylonian evidence of Engineers' visit to Earth.

8th century BC – the Prometheus myth (of a Titan who brought man to life from clay and stole the secret of fire from the Gods) first appears in Greek mythology.

620 BC – Mayan evidence of Engineers' visit to Earth.

1st century AD – The Engineers prepare a "death ship", filled with jars of black goo, to send to Earth in order to destroy their wayward children, humanity.

1990 – Peter Weyland is born.

2012 – Peter Weyland founds Weyland Corp.

2015 - First permanent colony established on the Moon, terraforming begins in earnest just over a decade later.

2023 – Weyland gives a TED Talk and acquires first patent for Method and Apparatus for Cybernetic Individuals.

c. 2030 – Weyland creates David, an android.

2032 - Commercial mining begins on Mars, paving the way for colonies there and on Titan later in the decade.

2033 - As faster than light speed travel becomes a reality, Weyland Industries launches the first FTL Space Exploration vessel, the Heliades.

2039 - The first breathable atmosphere is created for on an extrasolar planet - GJ 667Cc, 23.62 light-years from Earth, in the constellation of Scorpius - following the employment of a Weyland Atmosphere Processor.

2040 - Deep space research vessel Event Horizon launched to explore boundaries of Solar System. She disappears without trace near Neptune.

2040s - HD85512 B, Earth’s first off-world penal colony, is established by Weyland Industries.

Event Horizon. 2047 - Having picked up signals believed to be from the Event Horizon, a covert rescue mission is sent to recover the ship (which had actually been running an experimental new FTL system). The rescue ship, the Lewis and Clark, is lost. Two survivors are picked up 72 days later in the drifting remains of the Event Horizon. The entire incident remains classified to this day.

2060s - Several small colonies begin to take hold in the Outer Rim Territories,

2080s – Dr Elizabeth Shaw and Dr Charlie Holloway discover evidence of "star maps" from Babylonian, Sumerian, Mayan, Egyptian and Mesopotamian eras.

2089 – Shaw discovers another star map, or "invitation", in a cave on the Isle of Skye.

2091 – The USCSS Prometheus leaves Earth on its journey to LV-223.

January 7, 2092 – Ellen Ripley is born on Earth.

Alien: Prometheus. 2093 – All but two of the USCSS Prometheus crew are killed after an encounter on LV-223 with an alien species and a revived Engineer. The ship is destroyed. Dr Shaw and a severely damaged David leave on an Engineer ship to find the Engineers' homeworld.

2094 – Shaw rebuilds David, and the pair arrive at at the Engineer's world known as "Paradise". David uses the ship's toxic black-goo payload to destroy the entire population of Engineers.

2099 - The Weyland Corporation absorbs cybernetics rival Yutani; the Weyland-Yutani Corporation opens with the largest share value ever recorded on the Systems Exchange.

2101 - The United States Colonial Marine Corps is established.

2104 - South, Central, and North America form a financial collective, the United Americas.

Alien: Covenant. 2104 – Covenant, a colonisation ship carrying thousands of humans and embryos, takes a detour to an unnamed planet (Paradise) on its way to Origae-6. There the crew discover David and a new species, the neomorph.

The majority of the crew are killed, and David is revealed to have bio-engineered aliens (the "xenomorph"). He brings their embryos on board the Covenant. The ship continues its journey to Origae-6.

The Engineers Of 'Paradise'

2120 – Space vessel Nostromo leaves Earth.

Alien. 2122 – June 3: Nostromo lands on planetoid LV-426, having picked up what its crew believe to be a distress signal. Within 24 hours, executive officer Kane becomes an unwilling host to an alien, which then kills him and starts to pick off the crew one by one, leaving only Ripley and Jones, the ship's cat, alive.

2130 - Co-funded by the Weyland-Yutani Corporation, Gateway Station is constructed.

2157 - Hadley's Hope, a Weyland-Yutani terraforming colony, is established on LV-426.

Aliens. 2179 – Having drifted in stasis for 57 years, Ripley is rescued but ends up returning to LV-426 after contact with the new human colony there, Hadley's Hope, is lost.

Arriving with a squad of colonial marines, Ripley finds sole survivor six-year-old Newt, face-huggers, a swarm of aliens and a Queen. Ripley escapes with Newt, Corporal Hicks and android Bishop, and heads back to Earth in the Sulaco.

Alien 3. As Ripley, Newt, Hicks, and Bishop sleep, a facehugger, stowed away in the Sulaco, impregnates Ripley with a queen. A fire starts and the life pod ejects. Only Ripley and a single facehugger survive the crash landing near the penal colony on Fiorina 161. Ripley kills herself by jumping into a furnace, as the alien queen is born inside her.

2180 - A transmitted publication called Space Beast starts to circulate throughout the colonies, and is subsequently banned. The lengthy tome claims to have been written by Robert Morse, the last survivor of Fiorina 161, and reveal the true details of what happened before the penal colony was shuttered and abandoned by Weyland-Yutani.

The book is generally considered the ravings of a mad man, however it does stir up rumours of dangerous alien forms and company bioweapon experiments.

2183 - Today (Alien RPG)

Thanks to Digital Spy for doing the legwork!
With additional material from The Weyland-Yutani Report

A much more comprehensive timeline (with a parallel section for non-canon sources, such as the comics and novels) can be found here at The Alien Universe Timeline.