There have been a lot of research into this, and the hypothesis is that genesis was assembled from (at least) four different sources or oral traditions. The two

There have been a lot of research into this, and the hypothesis is that genesis was assembled from (at least) four different sources or oral traditions. The two creation stories are clearly from two different traditions, one calls the creator-god "Yahweh" (somewhat misleading translated to "The Lord" in English), the other uses the name "Elohim" (translated to "God" in English). The differences hints to different cultures: "Elohim" separates the waters and creates the dry land, "Yahweh" creates a spring in the desert. This could indicate that the one tradition originates from shore-dwelling people (water is the primary element, land is the exception), the other is from desert nomads (the dry land is primary, water is created by God). Note that the primary difference between the two psalms when seen in the diff view, is that one uses "God" one uses "The Lord". Hence they are probably the same original song filtered through two different traditions. When the Bible were assembled, the editors took pains to include all traditions, even when the content was overlapping.