Black Liquid (chemical A0-3959x.91 – 15) is a lethal liquid material created by the Engineers as a means to create human life.
The sacrifice Engineer drank some of the A0-3959x.91 – 15 in the beginning of Prometheus and his DNA began to fall apart, eventually resulting in him falling off of a cliff and into a lake where his DNA became mixed with the water and began to reassembled as human life.
Later in Prometheus, Elizabeth Shaw and her crew explored the Alien Temple where thousands of urns of the liquid was discovered. David 8 touched one of the liquid urns and it shortly began to ooze out of the urn at the same time the murals in the temple changed. David 8 manged to sneak an urn of A0-3959x.91 – 15 out of the temple which he later opened to discover the actual liquid.
Shortly after, he offered Charles Holloway an alcoholic drink which he poisoned with a drop of the liquid.
Holloway shortly after discovers that he is infected and later begins to scream and act aggressive as the rest of the crew tries to bring him back to the USCSS Prometheus. Holloway's skin turns a seemingly bright-greenish color and his blood veins turn black since the liquid can enter the bloodstream.
After Holloway was killed, it was later discovered that the Engineers had changed their minds about the creation of human life and decided to use the liquid to destroy human life rather than to create it. However, somehow the Engineers were infected with the liquid, leaving only one last Engineer who was still in hyper-sleep in a sarcophagus. When the last Engineer was awakened by David 8 and Peter Weyland, the Engineer killed Weyland and ripped David 8's head off. The Engineer planned to head for planet Earth and use the weaponized A0-3959x.91 – 15 to destroy human life. However, the Engineer was stopped by crashing to USCSS Prometheus into a Derelict which crashed.
A0-3959x.91 – 15 was also responsible for the creation of the Trilobite creature which was the result of Holloway having "sexual-relations" with Shaw while he was infected; impregnating Shaw with the Trilobite. The Trilobite later attacked the last Engineer as he a temped to break into a crashed escape pod. Hence, the Engineer was impregnated with the creature called Deacon.
A0-3959x.91 – 15 has different effects depending on how it enters the body or is ingested. It will cause an Engineer's DNA to fall apart. However, it will kill a human in only a matter of hours or make them go mad. It will enter a human's bloodstream within twelve hours and turn a human's skin into a dark-greenish color. It also causes extremely bloodshot eyes. It also caused small worm-like creatures to mutate into creatures called Hammerpedes.