Jord (pronounced “YORD;” Old Norse Jörð, “Earth”) is an obscure and seldom-mentioned giantess and goddess in Norse mythology. She plays no active part in the tales whatsoever, and is referenced only in passing as being the mother of Thor and as being the daughter of Nótt (“Night”) and Anarr (“Another”).
However, Thor’s mother is also called Fjörgyn, Hlóðynn, Fold, and Grund throughout Eddic and skaldic poetry. These names, like “Jord,” all mean “earth,” so, given the context, it’s unlikely that they were thought of as being truly distinct personages. But were they all different names for the same personage?
Such an interpretation seems to be overly literal. In all likelihood, what these passages are really saying is that Thor is the son of an earth goddess, but not necessarily any one specific earth goddess. “Earth” here seems to be more of a general concept than a discrete figure.
The Norse and other Germanic peoples were part of the larger Indo-European group of peoples. Throughout the Indo-European world – for example, among the Celts, Slavs, Greeks, Romans, and early Hindu society – the idea that femininity and the earth are intrinsically connected, as are masculinity and the sky, was one of the most basic and common ideas. This is borne out especially clearly in Celtic mythology (wherein all goddesses, with very few exceptions, conform to the earth/fertility/mother/sovereignty type), Aristotle’s cosmology, and the famous Indian marriage formula wherein the groom addresses the bride, “I am heaven, thou art earth.” The union of the sky god and the earth goddess, which maintains the cosmic order and bestows prosperity on the land as it’s fertilized by the sun and the rain, is often referred to as a hieros gamos or hierogamy, “divine marriage,” by historians of religion.
It would be extremely strange if this concept weren’t also found amongst the Norse and other Germanic peoples, and we can indeed find numerous examples of it. One example of the hieros gamos is the union between Thor and his wife Sif. Sif’s most-noted attribute is her long, flowing blonde hair, which is surely meant to be understood as corresponding to a field of grain ripe for harvest. Thor, whose name means “Thunder,” is the animating spirit of the storm whose rain fertilizes the fields.
Another Germanic goddess, Nerthus, was specifically identified with the Roman Terra Mater, “Mother Earth,” by the Roman historian Tacitus.
Another especially striking example of the Indo-European “earth mother” archetype amongst the Germanic peoples comes from an Old English prayer to an Erce, eorþan modor (“Erce, mother of earth”). The charm was recited when the plow cut the first furrow of the growing season, and milk, honey, flour, and water were poured into the soil.
Ultimately, then, when the Old Norse poets referred to Thor’s mother as “Earth,” they seem to have been referring more to a general concept that was ambient and taken-for-granted in their society than they were to a particular mythological figure. The fact that the references to her in Old Norse literature are so sparse and insubstantial lends further credence to this interpretation. Before the Norse and other Germanic peoples were converted to Christianity, their sacred tales and divine personalities were never systematized or rationalized like they are in modern storybook versions of mythology. They wouldn’t have necessarily felt a need to explain exactly who Thor’s mother was. That she was “Earth” was apparently enough.
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 These references occur in:
Haustlöng, stanza 14.
Þrymskviða, stanza 1.
Lokasenna, stanza 58.
Snorri Sturluson. The Prose Edda. Gylfaginning, chapter 37.
Snorri Sturluson. The Prose Edda. Skáldskaparmál, chapter 4.
 Gylfaginning, chapter 9.
 Simek, Rudolf. 1993. A Dictionary of Northern Mythology. Trans. Angela Hall. p. 179.
 Eliade, Mircea. 1959. The Sacred and the Profane: The Nature of Religion. Trans. Willard Trask. p. 118-147.
 Turville-Petre, E.O.G. 1964. Myth and Religion of the North: The Religion of Ancient Scandinavia. p. 188.