Mankind proliferates; Adapa's line serves as royalty.
Defying Enlil, Marduk espouses an Earthling female.
Celestial disturbances and climate changes affect Lahmu.
The lgigi descend to Earth, seize Earthling females as wives.
The promiscuous Enki begets a human son, Ziusudra.
Droughts and pestilences cause suffering on Earth.
Enlil sees it as fated retribution, wants to return home.
Ninmah, aged by Earth's cycles, also wants to return.
A mystery emissary warns them not to defy their destiny.
Signs increase of a coming calamitous Deluge.
Most Anunnaki begin to depart back to Nibiru.
Enlil enforces a plan to let Mankind perish.
Enki and Ninmah start to preserve Earth's Seeds of Life.
The remaining Anunnaki prepare for the Day of the Deluge.
Nergal, Lord of the Lower World, is to issue the warning.

Nergal, Ninurta, and Marduk were put in charge of certain stations during this time. Enlil, Enki and Ninmah were realizing how much they've aged being on Earth and were debating leaving, but they weren't allowed back on Nibiru after asking multiple times to return for a short time. It was at this time Marduk brought his wife to Enki and told him she is of Earth, but also one of his bloodline.

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Enki knew if Marduk espoused a human he would never be allowed his rights as firstborn on Nibiru, but Marduk knew that neither on Nibiru or Earth were his rights existing. They had been trampled long ago. Enlil was infuriated by this decision and to Anu he brought the problem. However, Anu and the council found no rule against any of this, they would, however, refuse Marduk to ever return to Nibiru and give up his Princehood. Everyone on Earth was in agreement with this, even Marduk. Marduk's wedding gift would be a new domain above the Abzu. What followed was the aforementioned intermarrying of the Igigi with other Earthlings they would even threaten to destroy the Earth if their marriages aren't blessed. Enlil was witnessing one evil deed after another and he was not happy. Marduk would allow them all to live in his new domain. Ninurta was instructed to build a domain with the offspring of Ka-in in response to Marduk and his new people. In this time a new son would be born by Enki's seed. Ziusudra.

With Marduk and his men taking human women to marry there was much chaos, not only this but signs of Nibiru passing were happening again. More flares in the sun, the "net force" of the Earth acting strange ( these are most likely the ley lines). Plagues and starvations and tribulations before the deluge began. Enlil was infuriated by what had been happening on Earth. He saw humans as a virus at this time and wanted them to perish. This is why Enlil is seen as an enemy in the tablets, as he was finally putting his foot down on what had happened. No longer will the laws of the universe be ignored, promises broken, lies conjured. He wanted humanity to be done with as they never should have been created in the first place! Nibiru was returning, closer, as in the days of Tiamat, it would be closer to the Earth than ever before.

Source
These events grew worse and worse for several shars. The next time that Nibiru would go towards the sun, Nibiru's net force would be exposed to the Earth. Its protection will be gone. The ice would be dragged across the Earth and a deluge would occur, this was what was discovered between Earth and Nibiru's leaders. It was at this time that Galzu would come to Earth. He claimed to be an emissary of Lord Anu. He told Enlil, Enki, and Ninmah that if they were to ever return to Nibiru, they would grow ill and die. The three were saddened. They would remain on Earth. Enlil would summon a council of the Anunnaki and reveal the calamity coming and they would be brought up in chariots to wait out the calamity. No earthling would be allowed to accompany them. All of the Anunnaki were made to swear an oath that they would not reveal this secret to the Earthlings. Enki had a real issue with this, but Enlil revealed how much he twisted the earthlings time after time from what was originally declared.

From the very beginning, at every turn, the decisions by you modified were!
To Primitive Workers procreating you gave, to them Knowing you endowed!
The powers of the Creator of All into your hands you have taken,
Thereafter even that by abominations you fouled.
With fornication Adapa you conceived, Understanding to his line you gave!
His offspring to the heavens you have taken, our Wisdom with them you shared!
Every rule you have broken, decisions and command you ignored,
Because of you by a Civilized Earthling brother a brother murdered,
Because of Marduk your son the Igigi like him with Earthlings intermarried.
Who is lordly from Nibiru, to whom the Earth alone belongs, to no one is no longer
known!
Enough! Enough! to all that I say. The abominations cannot continue!
Now that a calamity by a destiny unknown has been ordained,
Let what must happen, happen! So did Enlil angrily proclaim;

Source

All of the Anunnaki would swear this oath. Enki would as well with pain. In Sippur they would leave records of all that had happened since their arrival in chests in case there would be survivors so they might know their history. Enki would speak with Ninmah about the planet. How Enlil had overlooked the other inhabitants of the planet, the animals born of Earth and some brought from Nibiru. They would take it upon themselves to gather the life essence of every animal on Earth so they could repopulate it when all is said and done. They would have some help of course, but two by two they would preserve these essences. At that time, Nergal reported that the white land (ice cap) was shaking. The time of the deluge had come.