Black Liquid

Chemical A0-3959X.91 – 15, more commonly known as the Black Liquid or the Black Goo, is a living, highly-mutable organic compound created as a biological weapon by the Engineers. It has the capacity to fuse itself to the biochemical structure of other life forms, mutating them and making them far more hostile, changing the host's DNA entirely or almost no recognition of the original host, potentially giving rise to new species.

It is the origin of the Hammerpedes on LV-223 and the Neomorph on Planet 4; as well as the indirect origin of the Deacon, the Planet 4 Xenomorph, and possibly all Xenomorphs. It was also responsible for wiping out the Engineers' settlement on Planet 4, with the help of synthetic android David.

Biology
The Black Liquid, as its name indicates, is a black amorphous compound of millions of microorganisms which behave as a single parasitic entity that can seemingly affect any faunal organism. The effects, however, are variable. Sometimes the Black Liquid merely kills victims, which it does by provoking nearly instantaneous deterioration of cells and tissues, resulting in a quick and gruesome death, as seen with the Planet 4 Engineers.

On other occasions, however, the Black Liquid merges itself with its host and mutates it, altering both its appearance and its behaviour, the latter becoming far more hostile. Creatures affected by the Black Liquid may give rise to entirely new species, as demonstrated by the Hammerpedes and the spores that give rise to Neomorphs.

Organisms mutated by the Black Liquid exhibit incredibly aggressive behaviour and seem to be instinctively drawn to attacking other life forms, including their former brethren. These individuals possess enhanced strength, physical resilience, and regenerative properties, being capable of withstanding multiple gunshots. They may also develop traits typically associated with Xenomorph biology, such as the characteristic acid blood of the species (as seen with the Hammerpede) and possibly a vulnerability to fire, given that flamethrowers appear to be effective against them.

Additional symptoms might differ based on whether the Black Liquid was contacted by skin or ingested. A Human male who unknowingly ingested it in his drink exhibited more nuanced symptoms at first, manifesting, among other things, as sexual arousal, long before the actual mutation took place. Most curiously, however, is that the pathogen found a way to his reproductive system and impregnated the man's partner, who became pregnant with a mutant creature known as the Trilobite. This creature later behaved similar to a gigantic Xenomorph facehugger, and implanted an embryo inside an Engineer, which gave rise to the Deacon. This means that the Trilobite and Deacon apparently result from a combination of Black Liquid and Human DNA, with the added possibility that the Deacon may have incorporated material from its Engineer host as well, much like a Xenomorph does. It's currently not known if the creation of these Xenomorph-like beings is the Black Liquid's intended final purpose or an accidental side effect.

In spite of its unstable nature at ambient temperature, the Black Liquid can be safely stored in Steatite Ampules, used by the Engineers for this purpose.

History
The Black Liquid was discovered by the crew of the USCSS Prometheus inside Steatite Ampules in an abandoned temple on the moon LV-223, orbiting the gas giant Calmpamos in the Zeta Reticuli System, in 2093. It appears to have been intended by the Engineers to be used as a weapon against Earth, but somehow the infection managed to spread to the Engineers themselves and exterminated most of them.

In 2094, the android David, having hijacked an Engineer ship, set the Black Liquid loose upon the Engineer population on Planet 4, which wiped out all of them. By the time the USCSS Covenant arrived, ten years later, David had perfected the creation of actual Xenomorph eggs, genetically engineered from combining specimens of the local fauna infected by the Black Liquid and possibly Engineer and Human material. One of these eggs produced a facehugger, which implanted an embryo on Chris Oram, giving rise to what might be regarded as the first modern Xenomorph.

However, this may not represent the origin of the Xenomorph species, as the images of what look like Xenomorphs were also found within the temple on LV-223, indicating that the Black Liquid might have been originally derived from pre-existing Xenomorphs, rather than vice-versa. In that case, it's possible that David's experiments didn't create a new species as much as restored one to its most ancestral form.

Appearances

 * Prometheus (2012)
 * Prometheus: Fire and Stone (2014)
 * Aliens: Fire and Stone (2014)
 * Alien: Covenant (2017)
 * "Alien: Infiltrator" (2021)