Why no animal life ?

As you have already suggested here, the mutagen/accelerant could have caused a xeno/neo/proto outbreak which is now on the top of the food chain and has wiped out all other life-forms. When the food is gone the aliens eventually die as well.

The other scenario is that there was a holocaust (electrocution) which wiped out all of the beings living there (engineers/hominids) perhaps due to the above?

Parkerparrot

The size of the wheat is possibly a result of slightly different environmental conditions + gardeners favouring larger sizes.  

Humans are growing larger as a species over time:  the ancient homo sapiens were much smaller than us.  "Big things have small beginnings," so an evolutionary process causes the species to progress from smaller to larger over time.  A similar process leads to a larger type of Engineer who eats the wheat, while the smaller ones are slaves who work the fields.

Those at the top of the food chain are the ones who eat most of the food.  The advent of farming leads to many changes in human culture, eventually creating divisions between haves and have nots.  After farming, we move to centralized city-states in the Fertile Crescent and Indus Valley from smaller, agriculturally-based egalitarian communities. Stock is taken: number systems, a mercantile class, and the Cuneiform language emerges. The "God-Kings" return to Earth at this point to see how far the human cultures have advanced, but they freak out when they see how fast it's now evolving. 

While playing around with bird skeletons in the lab, David starts looking at how an evolutionary process known as sexual dimorphism causes female birds to be much larger, on average, than male birds.  Things are the other way around in humans, so maybe sometimes small things do have big beginnings.  This could be what Ridley means about how evolution itself can be scary if approached from this angle. 

CarynDelacroix... That is a very interesting point You got there. And a very inteligent one, at that. The environment plays in to a great extent when it comes to evolution. In the Perm era (I believe) the atmosphaer had a very different composition compared to today, resulting in dragonflies big as eagles. Putting wheat on another planet with different circumstances could very much so lead to BIG wheat. Throw in the Engineers and black goo into the mix and... There you have it. 

I am so thrilled about this movie.

            " Bees have hives, man " 

You also bring up a really good point about the dragonflies as big as eagles.  The insect species can grow much larger if the environmental conditions are right.  But their body plans can sometimes limit how big they can grow (due to gravity).

Gravitational forces act upon the exo/endoskeletons; and gravity eventually causes the apple to fall from the tree.

The Apple branched off from the Pomegranate's ancient line after the gardeners started selecting for sweetness. Today there are over 5000 various types of apple; however, the pomegranate's ancient branch continues to be eaten by people who prefer pomegranates for whatever reason.  

Each type of "apple" has slightly different characteristics.  The Golden Delicious apples are the ones thought by many to be tasty.  In the Greek myth about Persephone, it's pomegranate seeds that Hades forces Persephone to swallow before he drags her to the underworld with him.  The Garden of Eden myth talks about Eve biting the Apple rather than the Pomegranate, because by that time the story had evolved...  

The River Styx (not Acheron) is the river by which the Gods made their Covenants with Hades and took their oaths.

Dr. Shaw has a degree in comparative mythology, but Daniels is the one who actually spends more time digging through the dirt and getting her hands dirty.  Shaw always had people doing the digging when she conducted archaeological digs, while Daniels spends more time considering ecosystems.

"There is nothing in the desert, and no man needs nothing." In a desert region, it's difficult to transform the environment into a habitat that fully supports life.  The Engineers are "mortal after all," so David understands that they require certain things. The Engineers need food and water like we do.  

The larger chest cavities of the Engineers would be what allows their lungs to filter air more effectively than us:  they need as much oxygen as we do (if not more) yet have ways of surviving in low oxygen environments for longer periods of time.  This gives the Engineer body plan advantages over humanity… Their large size and physique allows them to throw their weight around.  The smaller types of humans would be relatively powerless to stop some of the "higher-ups."

CarynDelacroix 

I just love the way how You get from insects to Apples to pomme granate to the river styx to Covenant!!! Wow!

But... (pause) A bigger body means more cells to transport oxygen to, wich allso means bigger lungs. Would i not be the case then that the Engineers would be more vulnerable to low oxygen conditions?

           " Bees have hives, man " 

I'm not too sure about the biological side of things yet with the lungs/chests.  People that live at higher altitudes are barrel-chested and can absorb more oxygen where the air is thin.  

I'm thinking the Engineers would require a lot more oxygen, as you say, but that they're able to take in so much air and filter it in a way that extracts as much oxygen as possible.  There's a certain amount of oxygen left over when we exhale normally.

Our lungs separate the oxygen from the carbon dioxide, nitrogen, and other gases in the air, but the plants need the carbon dioxide just as much as we need oxygen.  So the trees form part of larger lifecycles as producers.  The sun is the ultimate producer for that energy system, giving energy to the plants/trees etc.  If a planet isn't close enough to a sun to fully support life, we end up with a "shake 'n bake" colony where they need to artificially heat the surface of the planet ("bake").

When Prometheus started creating the goddess Aletheia out of clay, he had to go away from the workshop while she was baking in the oven.  His servant, Dolus (Trickery, who represents David/Davis) snuck into the workshop and decided to try his hand at creating his own version of Aletheia (Truth or Wisdom). Now there are two versions of Aletheia, or possibly even more if we include the Deacon's line... One of them is the real Aletheia, while the other one is a false version of her.

Just to clarify:  I think we'll be left uncertain if the Engineers or David created the eggs on this planet, or if Eggs/Xenomorph DNA is something that one group of Engineers stole from the others a very long time ago. There could be a few hints in the film that the Xenomorph's line is more ancient than the Neomorph and has been evolving for quite some time to get the opposable finger digits it's working on.  The Xenomorph is capable of manipulating its environment to suit its needs ("they cut the power"), so the opposable finger digits allow it to begin opening simple doors, pushing buttons on elevators etc.

CarynDelacroix

There's mythological traces all over this, everywhere! RS did'nt sleep during history an religionclass, that's for sure! And neither did You, I believe!

As for the xeno (a word that I actually don't like, since I am a purist and it first turned up i Aliens) theres no doubt they're intelegent, but in a different way from humans. when it comes to the origin of the biomechanical alien I am not sure what to make of it. It could be David but allso something else. "Something we have'nt seen..."

            "Bees have hive, man"   

"^are you a science-fictive biologist? hehe"

Hopefully one who does not like petting Space Cobras ;)

@airshaft_surprise

Indeed i think this is somewhat the general idea, that this place was indeed like the Garden of Eden, i think the Paradise reference has been all long to show us this place in context to The Garden of Eden this will play a role in a loose connection i am sure of it, this could be the Birthplace of Humanoid Life (Engineers or their Ancestors or even Descendants) which Humanoid life which includes our DNA Originated from.

@CarynDelacroix

Indeed we have to try and think if ways to explain this as i attempted to address in my previous post and simply having animals that simply fled from the effected area makes sense.

There are a few concerns with this, because we then have to ask what caused the Engineers or those beings to maybe only Populate this one area?  Are we left to assume this is the case?  Or have the Populated other areas on that World.

Which then we have to ask how come we dont see no more?

Surely David has not infected them all with Black Goo unless somehow when its released it will spread over the entire World...

I think maybe somekind of Energy Weapon could have done something to effect all life on the Planet apart from maybe Plant Life.

I would assume and especially if Humanoids inhabited other areas of this World that a Ancient Event wiped them out and over time the Fauna overtook and covered up all Evidence of a fallen Empire.

I think the Black Goo if in mass it lead to similar to the Sacrificial Scene could explain no life, because Life has been destroyed and broken down to kick start basic Microscopic life and the time frame has simply not been long enough for Evolution to Larger Organisms to take place.

Then those Charred or Soot covered Engineers/Humanoids remains do not appear to look like they have been infected by the Black Goo.... unless they was but then that Cathedral Complex had a Fail Safe Energy Weapon that would be used to prevent the spread of any infection by Zaping and Destroying Genetic Material so its no use and cant be infected and altered or maybe it just kills off the Black Goo itself.

But then we have to ask where did David get his Experiments.. And so i think that maybe some kind of Noah's Ark was built on Paradise that maybe those beings tried to get to before the Disaster had affected them.

@Parkerparrot and CarynDelacroix

Indeed in the ancient past, lifeforms did grow larger than they are today, and environmental forces impacted that the more life that evolves on a World the smaller indeed they seem to get (maybe this is why Chinese are smaller..  joke).

I think CarynDelacroix maybe you are reading to much into the Scientific Legitimacy of it all... maybe i have too as far as trying to figure out how this could be and this cant be etc...

We can only hope those behind the movie had done some of their Homework like you have for us to believe what we see in a more realistic way.

As you indeed made ONE massive Point

While not all Plant Life needs the helping hand of Organisms to help them Procreate, from animals eating the fruits to then be used to sow the seeds (via Defecation ) or via use of them to Pollinate like Insects are used for.

One thing i hope they have not Overlooked but maybe they have done... is indeed  Plant Life Needs CO2 and so there has to be some kinds of Organic Life to Produce this

Maybe this however is where the Cathedral comes in and the purpose of the Gold Structure on the Top?  A Terra-forming device?

Electricity and Electromagnetic Forces can be used to change elements and break apart some Chemicals, such as breaking down Water to Produce Hydrogen and Oxygen.

Science is even working out ways that Gold and Electricity can be used to create Oxygen from CO2, therefore not needing Plant Life to Re-cycle this for us..

Maybe this Cathedral has Technology that can reverse such experiments so that it can create from Oxygen everything Plant Life needs to survive?

As far as the WHEAT goes.. i think we have to assume that Shaw did not have any, i mean why would she smuggle some? she surely knew LV-223 would not support life like this and she assumed her only option was the Lifeboat.

So we have to assume it (Wheat) was native to Paradise, if the Engineers are connected to Paradise and we are connected to the Engineers, then why assume that Plant Life  (or some) could not have been brought to Earth from Paradise.

As far as Daniels saying it looks Planted, maybe she could tell it was or she could not figure out why Earth Crops would grow on a Alien World.

Maybe again inside that Cathedral was stored various crops and plant samples and so again this Building is like a Noah's Ark

Sorry people's correction, i should have said  Adam and Eve were plant eaters before the expulsion from the garden. sorry bouts that!

"So we have to assume it (Wheat) was native to Paradise, if the Engineers are connected to Paradise and we are connected to the Engineers, then why assume that Plant Life  (or some) could not have been brought to Earth from Paradise."

Yes, BigDave.

If David 8 was able to get his hands on any "egg" shaped Weyland-Yutani Corporation Bio-Replicator pods, then David 8 could produce "40 million seed varieties and plant DNAs." I am also quite sure David 8 could hack these pods for his own interests.

In the ten years in between the events of Prometheus on LV-223 and viewing David 8 on Paradise, David 8 could have harvested human technology from another colony or ship.