When Devtas lost their powers as Sage Durvasa cursed Indra. The Asurs took this as a great opportunity to attack Swarg-lok. The Devtas were powerless and thus lost the war and flewed from heavens to save their lives. They went to Brahama to seek help, who in turn them to Vishnu.
Lord Vishnu advised them to treat Asurs in a diplomatic manner. Devtas formed an alliance with Asurs to jointly churn the ocean for the nectar of immortality and to share it among them. Vishnu told Devtas that he would arrange such that they alone obtain the nectar.
The ocean was nothing but the Ksheer Sagar, the middle part of Garbodhaka Ocean where cosmic Vishnu resides. The churning of the Ksheer Sagar was an elaborate process. Mount Mandara was used as the churning rod, and Vasuki, the king of serpents, who abides on Shiva's neck, became the churning rope. The Asurs demanded to hold the head of the snake, while the gods taking advice from Vishnu, agreed to hold its tail.
As a result, the Asurs were poisoned by fumes emitted by Vasuki. Despite this, the gods and demons pulled back and forth on the snake's body alternately, causing the mountain to rotate, which in turn churned the Ksheer Sagar.
Actually, Samudra Manthan is nothing but the drilling of Ksheer Sagar bed where maximum density of dark matter exists. Driiling was done with the help of Nuclear power and the poisonous fumes emiited by Vasuki was nothing but the liberation of radiation from nuclear reactor present in this drill setup.
Devtas negotiated with Asurs inorder to fulfil the complete requirement of enriched nuclear material as Asurs had big source of enriched nuclear material as many of underworld and Patal Lokas were ruled by Asurs.
It is a great possibility that bottom of this drill setup or so called mount Mandara is equipped with a stationary drill bit which is kept at 1,00,000°C to 1,50,000°C). The molten ocean bed is pushed around the edges as the drill is forced downward. Massive amount of energy was required to heat the drill head and hence nuclear reactor came into play for generating controlled nuclear energy resulting in immense amount of radiation.
When Asurs realised that they have been tricked by Indra by giving the head side of Vasuki to them. Asurs knew that spontaneous emission of poisonous fumes while drilling can kill all the Asurs. Hence, they speeded up the drilling process due to which Halahal (Lethal Poison) came out from the mouth of Vasuki. Technically, it is nothing but the leakage of radiation due to extra throttle of the machinery given by Asurs. Later it was neutralized by Lord Shiva. Pouring of milk on shiv linga is a scienthific respresentation of cooling of nuclear reactor due to absorption of extra radiation / Halahal by lord shiva during samudra manthan.
This is the reason milk poured on shiv ling is never given as a Prasad because it indicates the byproduct of a nuclear reactor. This is the reason that ancient theories relate shiv ling to modern nuclear reactors.