Alien: Earth Just Revealed It Actually Doesn't Contradict Prometheus At All
Maybe all this canon is totally fine.

If there’s one thing Alien fans have given up on, it’s trying to sort out the complex and often contradictory nature of the xenomorph chronology. Even as early as 1986, when Aliens jumped forward in time and retroactively changed aspects of the backstory of both the Weyland-Yutani corporation and Ellen Ripley, fitting all the pieces together has sometimes felt like piecing a robot back together after it's been attacked by a xenomorph. With Alien: Earth, it’s understandable if the first two episodes made Prometheus fans feel like everything in that Ridley Scott flick (and Alien: Covenant, for that matter) has been subtly erased, if not contradicted outright.
And yet, with the third episode, “Metamorphosis,” there are two ways in which it seems Alien: Earth throws Prometheus a bone, even if by accident.
Spoilers ahead for Alien: Earth’s “Metamorphosis.”
Yutani has wanted a xenomorph for a while
Morrow (Babou Ceesay) has been around for much longer than we thought.
One revelation in this episode is that the cyborg known as Morrow has been working for Yutani long enough that he’s now speaking to a descendant of the original person he used to report to. In one crucial scene, Morrow reaches out to Yutani and doesn’t recognize her voice. The woman responds, “You used to know my grandmother...it’s been 65 years, Mr. Morrow.”
Alien: Earth takes place in 2120, putting it just two years before the events of the original Alien film. However, this also puts it 27 years after Prometheus. If Morrow has been working for Yutani since 2055, that indicates he’s been on the payroll since before Weyland and Yutani became the same company.
How does this work with Prometheus? Well, if we operate under the assumption that David only reverse-engineered the xenomorphs in Covenant, and the xenomorphs are far older, then it stands to reason that Yutani made some kind of discovery about these creatures before Weyland did. Granted, that’s a lot of headcanon, but if you fast-forward to Aliens, it starts to make a lot more sense. If we squint, both the Weyland and Yutani companies had an interest in the xenomorphs prior to the 2120s, which doesn’t have to contradict the expedition in Prometheus at all.
The tiny xenomorph tadpole has Prometheus vibes
Prometheus still exists. No need to erase it just yet.
When Prodigy gets the facehugger sample back to their base, and Kirsh dissects it, a small, wiggly, proto-version of the xenomorph is extracted. This is later put into Hermit’s old lung, which, presumably, is in the name of further creepy experimentation.
But the small, silver little baby xenomorph seems very in line with the little black goo things we saw in Prometheus. It’s not exactly the same, of course, but in that case, we were seeing some kind of basic primordial substance that the Engineers used to create all sorts of creatures. What we’re seeing in Alien: Earth is the more run-of-the-mill xenomorphs that exist outside of an alien laboratory run by the Engineers.
Of course, you don’t need to think about Prometheus at all with either of these small plot points in Alien: Earth. And, it's fair to say that it’s all murky enough that Prometheus hasn’t been erased. In fact, by the time Alien: Earth is done, it may be even more fun to watch the entire franchise in chronological order, starting with Prometheus, then Covenant, and finally, all eight episodes of this series.