What really were Engineers doing in the Prometheus movie and why did mission to destroy Earth failed?

I can give some Insight to these ;) but do not take what i say as Gospel, the Movie is still pretty Ambiguous and those working on the Project who make the Decisions (Producers, Director, Writers and Powers that be (FOX) etc) as they Pretty much just Change things as they go along... sometimes without Consideration of how it could Conflict stuff.

I will answer each Element as you wrote them.... i will USE like This for when i am referring to comments by those working on the Movie etc.  And normal for my TWO Cents...

1. Buildings with head on them.

These had gone through some Changes... but they were merely to be  Individual Research Facilities. The Engineers like to Show-Off what they Create like say the Ancient Egyptians. The END-PRODUCT like the Elongated Skull at the TOP was more for Dramatic Effect.... Originally ideas were just Engineer Head on them like the BIG HEAD we see in the Ampoule/Urn Room.

The Big Head is just a Monument to the Engineers...... it could be Speculated that it depicts a Specific Engineer of some Importance but could also be just to showcase the Engineers in General.  The Urns are Placed around the Engineer Head to maybe indicate their Achievement.... these URNS do Contain the Pathogen with the Effects we see in Prometheus.  The Basic Intention is these Urns have the Ability to Mutate/Evolve any Organism or Cell they come into Contact with.

2. Murals depict:

a. Engineer with hand that comforts some kind of alien creature.

There has NOT been given much of a Explanation for this.... what little is given is the Engineers like to SHOW OFF what they have Created... with Monuments and Murals and so they are of some Importance... but its NEVER explained. This kind of Birdy Creature as some call it, seems to be in a Fetal Pose, which implies its either (1) Submissive to the Engineer or (2) is New Born.

Its pose is similar to this from the Art Book/Concept.

The ENGINEER has a SCAR like a C-SECTION... like Dr Shaw.. (but this is open to Debate).

However when we look at the MYTHOS of Prometheus... and we look at some of the Murals of the Punishment of Prometheus, which include the ONE above which seems to be Similar to the Mural in Prometheus... just the Birdlike Xeno is Replaced with a Eagle.... i have Speculated that maybe these are Connected?

But nothing has ever been said about the Mural apart from THEY showcase the Engineers Creation while some are Easter Eggs... looking at the Mural in Question and the Prometheus Mythos and Mural ive shown, i can only ASSUME that maybe we could Speculate that a Engineer was Chosen to be a Sacrifice to Create something?  If we look at Dr Shaw and her C-Section could we Speculate that the Engineers could do a C-Section of a Organism before it has CHEST BURSTED!  Maybe... could a Engineer be Chosen for this ROLE.. and its Repeated over and Over... like the Punishment of Prometheus?  Was this a Punishment? we can only SPECULATE.

b. Xenomorph like hands holding opened egg

Again as far as i am aware this has NOT been Explained other than those working on the Murals had said they made Numerous Murals as a NOD to HR Giger and Easter Eggs.... The Egg is ONLY on screen for a Short Time and most would MISS it. If it is merely a Easter Egg then it can THROW US OFF... but this is NOT the only Wild Goose Chase... the Alien Covenant Poster had NOTHING to do with what we saw in the Movie.

Some USE this Mural as Proof the Xenomorph is Ancient however...  the Hands are more like that of the Beaked like Creature with the Engineer as shown prior. And so this does-not mean its the Xenomorph it could be that other Creature. (RS had said that the Xenomorph had NOT Existed at the Point prior to the Outbreak on LV-223).

c. Xenomorph/Deacon like creature on main mural.

Again this is NOT much Explained... only that it could be a Easter Egg, but someone who worked on the Mural had said that it DEPICTS the Deacon.

Something to Consider is it does-not look like a Xenomorph not Quite... it also does-not look like the Deacon at the End.... HOWEVER... Earlier Concept of the Deacon and also the Beasts from Earlier Drafts all look the Same as the Mural Organism which is more similar to the Neomorph.

d. Images of facehugger impregnating the Engineers.

These again are based on HR Gigers Early Face Hugger Concepts...

Again this lends to how it was merely a Easter Egg of sorts....

However if we take into Account the Earlier Drafts of Prometheus (Alien:Genesis and Alien: Engineers) then here is what the LOW DOWN is... the Engineers have a Creation Tool (Goo in Prometheus, Scarabs in early Drafts)... This TOOL can Consume the DNA of a Organism and then STORE this DNA, this Substance then can PASS that DNA onto other Life to create a Hybrid.

i) Engineer in Prometheus Consumes Goo, breaks down and his DNA is then Spred to Evolve Life on Earth.  In early drafts its Tiny Scarabs and then ONE goes and Bites a Primitive Female and Evolves her with Engineer DNA.

ii) Fifield in Prometheus comes into Contact with Goo and Mutates into a Toxic Avenger but other Concepts he becomes a Hybrid.  In  the Earlier Drafts he is BITEN by a Scarab from a URN and likewise becomes a HYBRID.

The Early Drafts... seem to indicate the Engineers had likely Discovered a Parasitic Organism, and they had attempted with the Creation Tool to Cross Hybrid many Experiments (like David was on Planet 4) and had Created a Number of Various Xenomorph/Neomorph/Deacon like Creatures.

Taking this into Account the Murals likely Depict the Engineers Efforts to use their Creation Tool to Create Hybrid Monsters until they Achieved their GOAL.. a Organism like the Mural (Neomorph/Deacon) and they then Sacrifice this to Collect its DNA with the Creation Tool to USE to EVOLVE LIFE... but a Outbreak put a STOP to their Plans.

3. There is green crystal on the stand, which probably was activated for... Something?

Again another Mystery with NO Explanation... but there was a Reason...

Originally it was the BOWL from the Opening Scene.

Now we see IF this is the SAME CUP.... then its Smaller to the Engineer which roughly by SCALE would mean our Engineer would be 13-14 Foot Tall. The Earlier Drafts and Concept had them at 15ft Tall... revised down to 12ft and then with Prometheus Drafts to 10ft but our Engineers in Prometheus were about 8ft Tall Suited and just under 7.5ft without the Space Jockey suits.

So what likely happened was they SAW this Scale Difference as a Issue and Conflict and so CGI Replaced it with the CRYSTAL.  If they had KEPT the Cup/Bowl then what i said before about WHAT seems to have been going on would make Sense...

Something to Consider... some see the Mural as Xeno and as Engineers God/Worship as its like Christ on the Cross...

Christ is depicted like this to SHOW US that he SACRIFICED HIMSELF for the Greater Good or Mankind/Immortality (Life after Death).  It is my OPINION and Conclusion that the Engineers had Engineered and Created the Mural Organism and saw it as Perfect...

They had then Sacrificed this Creation to Create the STUFF in the URNS for some Great Benefit.... but the Results was NOT as Expected... but when Humanity became a Problem the Result could be USED to DESTROY US... maybe they thought it could SAVE/EVOLVE them...

This Theory does FIT with the Original Idea... the Master Narrative where our Engineers were once like us, they had Engineered and Evolved themselves to LIVE for a LONG TIME.. but they wanted more they wanted IMMORTALITY... and believed they was on the Verge of this..... but they NEVER Achieved it.

The Closest we see to Immortality in the Franchise is via the Xeno-DNA with Ripley 8, she can Regenerate, but she has some of the Memories of Ripley... so the DNA had Transcended some of Ripley  Memories and Soul into Ripley 8

A kind of Re-Incarnation if you would.... this would GIVE a Great Reason for the Engineers Experiments with related Ancestor Organisms.

4. 3 of sleeping engineers had something bursted from their chests - pods are with holes in them.

5. Bodies of engineers seem odd

Ok well Originally some Engineers had given Birth to some Beasts and others Killed by such Beasts....

The Engineer Suits in Prometheus some show they are HOLLOW!

This could be as working on Props then Hollow is Lighter than a Filled Full suit etc.... However if we look at Prometheus... the Engineer Consumed the Goo and his Body basically Disintegrated in a Violent and Volatile Chemical Reaction.........

Ridley Scott had said that eventually Fifield and Holloway would have the same Fate (would have become nothing)...If we assume the Engineers suits are Pressured so they ACT like a Pressured Container.... then assume the Reaction with the GO is so Violent like the Reaction of a Mentho in a Bottle of Cola... they this Volatile Reaction would try to Escape.... this COULD explain the Holes as though the Dissolved Engineers Goo had Exploded from the Suits..

This Explains why the Beheaded Engineers Body/Suit was HOLLOW.... (No Bones).

The Head was Preserved however..............it had NOT like Dissolved, and so IF this is the CASE and lets Assume that Room somehow made the GOO inactive or would STOP it.... this would Explain why the Head is intact and the Body Suit was Hollow.

It would also give a Good Reason for the Engineers to RUN to that ROOM and SHUT the Door Behind them.... the Door Shuts before some could make it. And this could HELP to Explain as to WHY the URNS had ONLY started to Leak once that Door was OPEN and somehow the ROOM Environment was Compromised.

This should Answer most of your Points... again SOME is just Speculation by me based on Various Clues and Comments by those working on the Movie.

FINALLY

7. It seems there is terraforming engine or something inside this buildings, making me think that planet was thriving with life at some point in the past.

Indeed the Complex was Terra-Formed.... while OUTSIDE was Deadly to Humans.... however the Engineers can Survive on the Surface with NO MASK.

Which Begs the Question to WHY is the Complex Terra-formed so Humans can Breath?

Our LV-223 Engineers do-not need their Suits... the Suits likely are like a Bio-Hazard Suit... to Protect from the GOO... (but they still got Infected, i can give a Theory after). They maybe also NEED them for Space Flight.

The Atmosphere on Planet 4 can be Breathed by Humans and those Engineers on Planet 4 lack the like GILLS that the Necks of the LV-223 Engineers under Suits have.

I believe that if we look at the Star Map as NOT a Invitation but showing US that this is WHERE we came from.... thus making LV-223 a Outpost for Experiments and Evolution of Creations where when the Engineers are pleased with the Results they SEND/SEED them in the GARDEN (Worlds) so then LV-223 is a Nursery/Green House.

So the Engineers take their Creations back to LV-223 to then Evolve/Tweak us and then take us back etc.... should any of these Creations (Humanoids) Escape the Outpost they would DIE outside before they can get anywhere.

At some point the Engineers or a Faction had decided they wanted to ERADICATE their Creations and so LV-223 was turned into a Place to Engineer/Create something ELSE.... and these Experiments had lead to their Downfall (the Outbreak).

The NO WEAPONS... Question... if your a Ancient and Advanced Race who Visit and Control every Aspect of your Creations, and keep them to a Primitive Level Certainly like say Mankind like in Ancient Times, then maybe they DONT need Weapons to Deal with us.

When they was Experimenting with the Horrors connected to Xeno, Neomorph etc they would have NEEDED SOME... but seems in HUBRIS they did not.

This does-not mean they do-not have Weapons... the Earlier Drafts that had some kind of Weapon/Power like the FORCE in Star Wars where they could THROW like Invisible Waves of Energy at the Humans.  The Comics gave the Engineers a Energy Weapon/Blaster.... but when dealing with a Ancient and Advanced Race then their Technology/Weapons could be BEYOND what we could Comprehend of be Familiar with......

Some of the plotlines to the ALIEN RPG dabbled on the Black Goo side of the franchise.

I know I'm not very good at writing entire paragraphs to explain my thoughts so I tend to write single sentences most of the time.

Regarding the Black Goo it was something that was Quite Simple to begin with, which then got a little Muddled with the Comics and with Alien Covenant it became some what of a MCGUFFIN....

The Early Conception with say Alien Engineers/Alien Genesis was that we came from the Engineers via their DNA was Imprinted onto us in the Past.

It is Implied this was from the Sacrificial Scene... which in those Drafts was as Follows.

1) Elder Engineers give the Younger Engineer a Black Box, in which there is a Cake of Dark Sticky Material.... from this comes Tiny Scarabs.

2) The Engineer brings this Cake Substance to his Mouth and the Scarabs Swarm him and they Bite the Engineer, they begin to Devour Him (we Zoom into Microscopic Level and see Cells Rapture, Protein and DNA Unravel) The Scarabs fill themselves with the Genetic Material.

3) The Engineer is seen bring Devoured and he takes a Cruciform Pose (like Christ on the Cross) while the Scarabs are eating him from Head down until what remains of his Body just Falls down while it is still being consumed. and then his Body (essentially these what must be Hundreds of Thousands of Tiny Scarabs Eat the Engineer until NOTHING much remains).

4) We then arrive at a Scene of a Primitive Woman... and a Black Scarab arrives and lands on her Neck and Bites her.... INJECTING a Cargo of DNA (when then go to Microscopic Level again and see her Cells are being Changed by the DNA the Scarab has Injected) We then see a External Shot of her with Pupils Dilated with shock, she looks at her Hand and the Scarab then just disintegrates to DUST.

This SCENE implies that these Scarabs can Consume a Organism Molecule by Molecule, and they then STORE this Organisms DNA.  These Scarabs will then go off and Find other Life and INJECT the DNA of the Organism they Consumed into a New Host which will INFUSE the DNA and Create a Hybrid.

The Next Time we see Scarabs is in the Engineer Complex, stored in URNS/JARS...

a) Fifield runs off after Milburn is attacked by a Centipede like Creature, as he runs he then runs into a Resinous Jar and it Breaks, it releases a cloud of Motes that are Tiny Scarabs, and they Swarm him, and he Swats them and Kills some and they Produce a ACID which then allows the Scarabs break into his Helmet Visor and then ONE BITES him.

b) We enter a Microscopic Level again and see ALIEN DNA that Invades his own DNA, similar to what happened to the Primitive Woman.

c) However Fifield is Mutated into a Beast with Elongated Skull, Longer Limbs a Horrific Hybrid, which when its KILLED has ACID BLOOD.

This shows the Scarabs stored within the URNS pass on a ALIEN LIKE DNA there was a Number of Concepts drawn but this Fifield is FAR more ALIEN than we saw in Prometheus.... this SCENE seems to imply these Scarabs had Consumed this ALIEN DNA from something....... which would indicate the Engineers had USED these Scarabs which are essentially a TOOL to Capture DNA from one Organism and PASS this onto another to Create a Hybrid.

So this means the Engineers used this Hybridization Tool on some ALIEN ORGANISM which is likely the Octopus looking Face Huger that infects Holloway in these Drafts. The Result is they take the Scarabs after they consume a Organism and STORE the Scarabs in URNS which are USED to Drop onto WORLDS to then INFUSE the DNA the Scarabs have Stored onto Life on this World a much more Efficient Method than the Engineer Sacrifice.

BARE THIS IN MIND...... as it helps to make sense of PLANET 4 and WHY the Engineers welcomed the Juggernaught... but this is for after.

NOW.... when we get to Prometheus we have the Sacrificial Scene which could imply this is HOW the Engineers DNA got to become US, but RS had mentioned the Engineers do this on Many Worlds and they Return over and over to Continue with such Evolution.

Here the BOX is replaced with a CUP/BOWL and the Black Sticky Cake is replaced by a TAR like Substance that begins to Dissolve into a Liquid.

The Urns we see in the Ampoules is a Black like Substance that looks like as if you had some Ground Coffee in Water or other Tiny Particles..... which when Activated will Mix with the Water/Liquid to Ooze into a Black Slick Oil like Substance.

Prometheus gets a bit Confusing based on its Various Infections...

I) Hammerpede comes from the GOO infecting in Large Dose those Worms the Crew had brought in to the Complex from outside.

II) Fifield becomes a Mutant, his Exposure vs his Size is NOT as High Dose, its keen to mention other Concepts again we see Fifield is LESS HUMAN than we end up with.

III) Dr Shaw is infected by some of the GOO either Evolving some of Holloways Sperm Cells or the GOO itself infects one of her Eggs.  As the Egg Cell is a Base for Life (most Stage 1 Embryos of Life on Earth all look the same/similar) then it has LESS DNA to Re-Write and so the RESULT would be something that has MORE DNA of what the BLACK GOO contained.

IV) Holloway is a Enigma, he only has a Small Dose, which he passes on to Dr Shaw in smaller Dose (or Mutated Sperm) Holloway seems to get unwell and then his Skin Turns Grey..... he is Killed before we see the Full Effect, but RS had said he was suffering the same Effect as Fifield and the Engineers who died just more SLOWLY.

V) EYEWORM... The Eye-worm we saw with Holloway is Interesting and a Puzzle but some of the UNUSED PROPS/EFFECTS we see when Holloway begins to turn GREY we see small Worm like things growing out of his Skin.   These could be his EVOLVED SPERM CELLS..

Or it could mean that the Tiny Scarabs from earlier Drafts had become Tiny Worm like things....

something to NOTE is that Human Sperm Cells may look like Tadpoles under the Microscope but the Collection of Millions of these without just appear as a STICKY GOO.... thats some Food for Thought....  i conclude its likely the Scarabs where replaced by Tiny Worm like Parasites... but the FUNCTION is the SAME.

IF we assume this is CORRECT then the GOO is actually Easy to Understand just as the Scarabs were in the Early Drafts....

So if we took the BASE (Scarabs/Worms) and released them on a WOLF.. then we collected the Scarabs/Worms/Goo after the WOLF has been Consumed and then release these Scarabs/Worms/Goo on a Human you would get a WEREWOLF.

Do the same with a CAT and you get THUNDERCATS... with a Turtle you get TMNT etc.....

Take one of these Werewolves and infect them with the BASE and then collect the Result and release this on the Thundercats and we could Speculate you would have a 25% Wolf, 25% Cat and 50% Human Hybrid.

If we consider such a Theory as Accurate... this basically is WHAT we saw that David was doing on Planet 4, using the GOO in many ways to Take Traits from Various Organisms inc the Neomorphs to make various HYBRIDS.......

This Process seems to be indicated in the earlier Drafts of Prometheus (Alien Engineers/Genesis)...... so you SEE the GOO if we look at it in this WAY is Pretty Easy to Explain and FITS with everything we are shown....

Apart from the Planet 4 Bombardment.... but i have a few Theories on that.

I just wanted to talk about the ALIEN RPG's supplemental lore on the black goo.

The RPG modules: Core Rule Book, Chariot of the Gods and Heart of Darkness adds additional lore bits such as giving a semi-official name to the Planet 4 Xenomorph, called a Preatomorph, in-place of the fan named Protomorph.

The deacon and trilobite are now collectively classified as Protomorphs. Those exposed to the black goo are divided into main categories. Anathemics are based-on Halloway's and Fifield's condition and the other who's name I can't recall at the moment are based on early concept of Fifield's Condition.

I see the RPG was trying to make sense of it all....

But in Regards to the Movie Canon.... we cant be sure if they will STICK to what the RPG Books had attempted to show... we will get some idea after the Movie and TV Series and any Comments that RS makes in the Aftermath.

I wish that we'll get more about the Engineers, and not a repeat of what we've been given a lot. The franchise also contains various things, they don't need to have the Xeno every time. Please don't make it all about androids, and also give us human characters to care for that are well-written.

Thoughts_Dreams

You would probably get a kick out of the ALIEN RPG then, they add new aliens to the lore and I'm not just talking about xenomorphs. even if you are not into tabletop RPGs the game books are filled with additional lore bits that the films are too afraid to go.

Strange new normal alien animals

The Arcturians are given more attention

The black goo makes more monsters than just xenomorphs.

The Deacon and Trilobites now collectively part of the protomorph-line is explored more.

The Praetomorph "aka Planet 4/David's xenomorphs" are explored more.

Those exposed to the black goo are explored more.

So far they haven't explored too much of the Engineers yet, but hopefully we get an Engineer lore book.

Politics concerning the human-side of the alien franchise is explored more.