The texts in the Poetic Edda are considered older than those recorded in the Prose Edda. The Poetic Edda consists of ancient Norse poems, the mythologies and legends recounted in a specific style of stanzas found only in the Icelandic texts, a written version of ancient Nordic oral traditions. As such, the poems recorded in the Poetic Edda and are very different to the format in the Prose Edda.
In the Poetic Edda, Yggdrasil is a prominent and common element recounted in the various Norse myths. From one poem, the Hávamál, a tale of how Odin gained the runes. Odin hangs himself from the Yggdrasil after being speared and refuses aid from the other gods, enduring without sustenance for nine days. While Odin hangs from Yggdrasil over the Well of Urd, he observes the Norns and the working of the runes and wills the runes pass the knowledge of their working to him. Odin offers this sacrifice, placing himself between life and death with the knowledge that the runes could only be learned by someone truly desiring and of proven merit. After the ninth night hanging precariously in a state of half-death, Odin is rewarded with the knowledge of the runes and the wisdom it grants him. Another important poem, the Voluspa from the Poetic Edda, recounts the prophecy of a volva, a seeress. A volva was a practitioner of Seidr, the prophetic magic learned by the women and first taught by the goddess Freya, originally of the Vanir before joining the Aesir after the war between the two. In part of the Voluspa, Odin’s quest for knowledge is referenced again. The volva refers to how Odin became one-eyed, sacrificing his eye to the Well of Mimir in the quest for wisdom. Once the sacrifice was made, Mimir allowed Odin to drink from the well, taking from the waters the insight contained within.
Similar to the story of Odin in the Hávamál, knowledge was not considered attainable without a sacrifice. Clearly, Odin places high value on knowledge and the wisdom gained is invaluable in his ability to protect the Aesir from misfortune. In another part of the Voluspa, the volva foretells the coming battles and events leading to Ragnarok. A reference is made to Heimdallr, the watchman of the Aesir, linking the god with Jotunheim, where he will collect his horn, Gjallarhorn, to summon armies in aid of the Aesir during Ragnarok. Several arguments suggest the name Gjallarhorn is derived from Gjoll, one of the eleven rivers flowing from Jotunheim. The Well of Mimir is also located in Jotunheim and thus, the prophecy of the volva links all events leading to Ragnarok back to Yggdrasil whereby thematically, Fate connects all. Despite the un-making of the cosmos dealt by Ragnarok, Yggdrasil catches fire but endures, enabling the new cosmos to begin.