In the following passage from Act 1, Prometheus addresses the earth, referring to it as "Mother" of the "Titans," of whom Prometheus is one. This is an allusion to Greek mythology (specifically, the aspects of Prometheus's story that precede the events of Prometheus Unbound):
I hear a sound of voices: not the voice
Which I gave forth. Mother, thy sons and thou
Scorn him, without whose all-enduring will
Beneath the fierce omnipotence of Jove
Both they and thou had vanished like thin mist
Unrolled on the morning wind. Know ye not me,
The Titan?
In the original mythos, to which Shelley alludes, Prometheus's Mother Earth is named Gaia; she gave birth to everything at the beginning of creation, including the Titans—forefathers of the traditional Greek gods. Jupiter is the oldest (or youngest, depending on how one interprets the myth) son of the Titans Kronos and Rhea, whom he overthrew in his quest for power on Mount Olympus.
It is worth noting that throughout Prometheus Unbound, Shelley combines Roman and Greek mythology into one entity. While the gods are usually invoked by their Roman names (Jupiter/Zeus, Mercury/Hephastus), other Greek aspects are retained. In general, the story of Gaia remains the same between mythological retellings.
