Norse cosmology is the study of the cosmos (cosmology) as perceived by the ancient North Germanic peoples. The topic encompasses concepts from Norse mythology, such as notions of time and space, cosmogony, personifications, anthropogeny, and eschatology. Like other aspects of Norse mythology, these concepts are primarily recorded in the Poetic Edda, a collection of poems compiled in the 13th century, and the Prose Edda, authored by Icelander Snorri Sturluson in the 13th century, who drew from earlier traditional sources. Together these sources depict an image of Nine Worlds around a cosmic tree, Yggdrasil. Time and space Concepts of time and space play a major role in the Old Norse corpus's presentation of Norse cosmology. While events in Norse mythology describe a somewhat linear progression, various scholars in ancient Germanic studies note that Old Norse texts may imply or directly describe a fundamental belief in cyclic time. According to scholar John Lindow, "the cosmos might be formed and reformed on multiple occasions by the rising sea." Cosmogony Drawing in part on various eddic poems, the Gylfaginning section of the Prose Edda contains an account of the development and creation of the cosmos: Long before the Earth came to be, there existed the bright and flaming place called Muspell—a location so hot that foreigners may not enter it—and the foggy land of Niflheim. In Niflheim was a spring, Hvergelmir, and from it flow numerous rivers. Together these rivers, known as Élivágar, flowed further and further from their source. Eventually the poisonous substance within the flow came to harden and turn to ice. When the flow became entirely solid, a poisonous vapor rose from the ice and solidified into rime atop the solid river. These thick ice layers grew, in time spreading across the void of Ginnungagap. The northern region of Ginnungagap continued to fill with weight from the growing substance and its accompanying blowing vapor, yet the southern portion of Ginunngagap remained clear due to its proximity to the sparks and flames of Muspell. Between Niflheim and Muspell, ice and fire, was a placid location, "as mild as a windless sky". When the rime and the blowing heat met, the liquid melted and dropped, and this mixture formed the primordial being Ymir, the ancestor of all jötnar. Ymir sweated while sleeping. From his left arm grew a male and female jötunn, "and one of his legs begot a son with another", and