Also, as an interesting aside, in playing through this level with a friend one time, I made reference to Guilty Spark’s ‘duplicitous’ dialogue and actions throughout the remainder of the game. I feel that this word fits him perfectly due to the nature of his behavior in ‘helping’ the Chief and the Arbiter.

http://blog.ascendantjustice.com/halo-3/the-terminals/

Also, we know that the Dreadnought outputs enormous amounts of energy because it had been powering the entire city of High Charity (at partial-power) for some time, as revealed to us by Cortana in the level “Gravemind,” in Halo 2.

secondly, so many of you refer to the incredible amounts of power outputted by the forerunner ship. I know I am missing something, as I had never heard anything about the SPARTAN-I program, but I do know that the covenant had only unlocked about 20% of the dreadnought’s engine power. that may stll be an incredible amount of power, but it doesn’t seem that way to me. this is speculation, but I think that they were barely able to get enough power out of the ship to operate high charity, and it certainly seems reasonable that they had an auxilliary power source (especially since you blow it up in h3).

hooka

1. Johnson is immune to possession by flood due to a case of Boron’s Syndrome, which is simply put a
distortion in the nervous system.

“It has been shown that prolonged exposure to the radiation emitted by plasma grenades, without proper protection, can cause a deviation in the neural electric pathways of the user–a disorder called Boren’s Syndrome.” -From Halowiki.net

Dr. Halsey speaking to Chief about Johnson in First Strike (by Eric Nylund. pgs 244-246)(I only put in conversation text. There is more description about their environment and actions in the story that is not here.)

Halsey: “He was diagnosed with Boren’s Syndrome.”

Chief: “I haven’t heard of it.”

H: “I’m not suprised. It’s caused by exposure to high-yield plasma. Like the burst released by a Covenant plasma grenade. We don’t see many cases- people usually die from the direct effects of those weapons long before these secondary symptoms manifest. Apparently the Sergeant captured a crate of plasma grenades from the Covenant during the Seige of Paris IV. He used them all- received a commendation for bravery… and a twelve-hundred-rad cumulative dose of radiation as an unanticipated bonus.”

C: “I don’t see the connection between the Sergeant’s sickness and his surviving the Flood.”

H: “Boren’s Syndrome is characterized by migranes, amnesia, and brain tumors… and without treatment, death. It disrupts the electrical signals in a person’s nervous system.”

C: “Is it treatable?”

H: “Yes, but it requires thirty weeks of intensive chemotherapy. Which brings me to this.” She hit the NEXT PAGE key and official “Refusal of Treatment” document appeared on the screen. “The Sergeant did not wait thirty weeks to get back and fight.”

C: “How did this disruption of his nervous system save him?”

H: “I’ve deconvoluted the biosigns of the soldiers overtaken the Flood. The parasite interfaces with a host by forcing a resonant frequency match to each host’s nervous system.”

C: “And the Sergeant’s nervous system is so jumbled that the Flood couldn’t force a match.?”

H: “Correct. Further blood tests show his system bearing traces of Flood DNA- very much dead and noninfectious, but some gene fragments are intact. I believe this is proof of a failed attempt to possess him. It also appears to have imparted him with some curious regenerative abilities, although I cannot yet fully confirm this side effect.”

C: “I think I see.”

H: “No, You don’t.”

C: “Doctor?”

H: “Discovering how he survived is not what I want to talk about. It’s what happens next to Sergeant Avery Johnson. I’ve prepared two separate reports on this for ONI Section Three. The first has all the relevant data on my analysis and the possible technology to counter an initial Flood infestation. The second includes the source material: Private Jenkin’s and Sergeant Johnson’s mission logs and the Sergeant’s medical files. I leave it up to you which to deliver to Lieutenant Haverson.”

C: “Why would I withhold any data, Doctor?”

H: “For a long time I had thought that we had to sacrifice a few for the good of the entire human race. I have killed and maimed and caused a great deal of suffering to many people- all in the name of self-preservation. But now I’m not sure that philosophy worked out too well. I should have been trying to save every human life- no matter what the cost. If you give ONI the first report, they may be able to find a countermeasure for the Flood. Maybe. They would have a slightly better chance, however if you gave them the second report.”

C: “Then I’ll give them the second report.”

H: “Which will murder Sergeant Johnson. ONI will not be satisfied to take a sample of blood. They will dissect him to find out he resisted the Flood. It would be a billion-to-one shot that they’ll ever replicate his unique medical conditions- but they’ll do it anyway. They will kill him because the trade-off is worth it to them. Is it worth it to you John?”

C: “Why do you want me to make this choice?

H: “One last lesson. I’m trying to teach you something it’s taken me all my life to realize. I’m giving you the chance to make the decision that I thought I couldn’t make. I’m sorry. Linda is almost ready for surgery, and I have several things I must accomplish before then. You should go.”

C: “Doctor, don’t let her die again.”

END CONVERSATION (First Strike by Eric Nylund. pgs 244-246)

2. The rings destroy all of the Flood’s food which is any sentient life or life with enough biomass to support them.

Level: Two Betrayals (Halo: Combat Evolved)

{Opening cinematic—Long shot of the Control Room. Master Chief and 343 Guilty Spark teleport in, obviously in the middle of a conversation}

343 Guilty Spark: “…Which means that any organism of sufficient mass and cognitive capability is a potential vector.”

(Master Chief pauses)

343 Guilty Spark: “Is something wrong?”

Master Chief: “No, nothing.”

343 Guilty Spark: “Splendid. Shall we?”

{Master Chief and 343 Guilty Spark move up to the main panel.}

343 Guilty Spark: “Unfortunately, my usefulness to this particular endeavor has come to an end. Protocol does not allow units with my classification to…perform a task as important as the reunification of The Index with The Core. That final step is reserved for you, Reclaimer.”

{Master Chief takes the Index, and puts it into a slot on the console. Lights and holograms appear, but then fade.}

343 Guilty Spark: “Odd, that wasn’t supposed to happen.”

{Cortana suddenly appears over the console.}

Cortana: “Oh, really?!”

{There is a flash of light, and 343 Guilty Spark is thrown back, and down to the ground.}

Master Chief: “Cortana?”

Cortana: “I’ve spent the last 12 hours cooped up in here, watching you toady about, helping that thing get set to slit our throats!”

Master Chief: “Hold on now, he’s a friend.”

Cortana: (Mockingly) “Oh? I didn’t realize. He’s your pal, is he? Your chum? (Angrily) Do you have any idea what that bastard almost made you do?!”

Master Chief: “Yes… Activate Halo’s defenses, and destroy the Flood, which is why we brought the Index to the Control Center.”

Cortana: “You mean this?”

{Index hologram appears in Cortana’s hand.}

343 Guilty Spark: “A construct?! In the core?! That is absolutely unacceptable!”

Cortana: “Sod off!”

343 Guilty Spark: “What impertinence! I shall purge you at once!”

Cortana: “You sure that’s a good idea?”

{Cortana’s avatar absorbs the Index.}

343 Guilty Spark: “How… How dare you! I’ll-”

Cortana: “Do what? I have the Index! You can just float and sputter!”

Master Chief: “Enough! {The Chief brings both hands up in the middle of them as if to stop a fight then turns back round to Cortana} The Flood is spreading. If we activate Halo’s defenses, we can wipe them out.”

Cortana: “You have no idea how this ring works, do you? Why the Forerunners built it? Halo doesn’t kill Flood, it kills their food. Humans, Covenant, whatever. We’re all equally edible. The only way to stop the Flood is to starve them to death. And that’s exactly what Halo is designed to do; wipe the galaxy clean of all sentient life. You don’t believe me? Ask him. (Points at Spark)”

{Master Chief hesitates, and then turns to 343 Guilty Spark}

Master Chief: “Is it true?”

343 Guilty Spark: (pauses) “Of course. Technically, this installation’s pulse has a maximum effective radius of twenty-five thousand light years. But, once the others follow suit, this galaxy will be quite devoid of life, or at least any life with sufficient biomass to sustain the Flood.” (pause) “But you already knew that… I mean, how couldn’t you?”

Cortana: “Left out that little detail, did he?”

343 Guilty Spark: “We have followed outbreak containment procedure to the letter. You were with me each step of the way, as we managed this crisis.”

Cortana: (Alarmed) “Chief, I’m picking up movement!”

343 Guilty Spark: “Why would you hesitate to do what you have already done?”

Cortana: “We need to go, right now.”

{Sentinels float up behind 343 Guilty Spark}

343 Guilty Spark: “Last time, you asked me, if it was my choice, would I do it? Having had considerable time to ponder your query, my answer has not changed.”

{Master Chief looks around at the Sentinels, and backs towards the panel. He takes Cortana’s disk out of the console, and inserts it into his head.}

343 Guilty Spark: “There is no choice. We must activate the ring.”

Cortana: (whispers in Master Chief’s head) “Get. Us. Out. Of. Here.”

343 Guilty Spark: “If you are unwilling to help, I will simply find another. Still, I must have the Index. Give your construct to me, or I will be forced to take her from you.”

Master Chief: “That’s not going to happen.”

343 Guilty Spark: “So be it. Save his head. Dispose of the rest.”

{343 Guilty Spark teleports away, and his Sentinels attack}

{Cutscene ends}

In this conversation, Cortana states that the rings destroy all sentient life.

Definitions of sentient:

1) http://www.merriam-webster.com/dictionary/sentient

Main Entry:
sen·tient Listen to the pronunciation of sentient
Pronunciation:
\ˈsen(t)-sh(ē-)ənt, ˈsen-tē-ənt\
Function:
adjective
Etymology:
Latin sentient-, sentiens, present participle of sentire to perceive, feel
Date:
1632

1 : responsive to or conscious of sense impressions
2 : aware
3 : finely sensitive in perception or feeling
— sen·tient·ly adverb

2) http://www.yourdictionary.com/sentient

Definition
sen·tient (-s̸hənt, -s̸hē ənt)(adjective)

of, having, or capable of feeling or perception; conscious

Etymology: L sentiens, prp. of sentire, to perceive by the senses: see sense

sentient Related Forms:
sen′·tiently (adverb)

sentient Synonyms:

conscious, aware, alert, perceptive; see observant 1, sensitive 3.

These definitions state that the anything that can perceive itself or things around it is sentient. (I don’t have proof from a dictionary from this one but I have also been told that the term sentient means is able to feel pain and then react accordingly.)

343 Guilt Spark states that the rings eliminate the Flood’s food source, which seems to be anything about the size of an average human or larger from the biological taxonomy system in the Animalia kingdom. This means that all life smaller than the average human and all life in the Plantae, Fungi, Protista, and Monera kingdoms is safe from the effects of the discharge of the Halo installations when they are fired. (info on the biological taxonomy systems can be found here: http://en.wikipedia.org/wiki/Kingdom_(biology))

These are just some of my thoughts about what people have said in their own comments. I hope that my evidence supports what I tried to clarify for you guys. Also to the guys doing these posts I throughly enjoy them and commend you on your more than excellent work.

If you look across near the hole you go into to finish the level, you will notice Elite Ultras (white armor) engaging the flood as they move towards the ships “entrance”. I suppose they would be the dead elites you find. Flood do pop out of the whole as you make away. I assume they overpowered the elites.

The Cruisers on the other hand, are CCS-Class BattleCruisers, the more common 1-mile long ships. The Truth and Reconciliation is a popular example of a CCS-Class BattleCruiser.

When the captured flood ship exits slipspace within Earth’s atmosphere, it appears to be trailing some kind of smoke/gas. I don’t find it too difficult to believe that some of this smoke would contain tiny flood spores. Now, depending on how high up the ship was when it first exited slipspace, it seems likely that the wind would carry some of these spores far away from Voi and the Elites’ means (glassing) of containing the infection.

And as Vadum says - “One single Flood spore can destroy a species.” The Forerunner were unable to stop the flood once it made contact with one of their worlds. It’s difficult to believe that the act of simply glassing Voi and the surrounding area saved Earth from the parasite.