Artwork by Josephine Wall
Hesiod's Theogony tells how, after Chaos, "wide-bosomed" Gaia (Earth) arose to be the everlasting seat of the immortals who possess Olympus above, and the depths of Tartarus below. He then tells that Gaia brought forth her equal Uranus (Heaven, Sky) to "cover her on every side" and to be the abode of the gods. Gaia also bore the hills, and Pontus (Sea), "without sweet union of love" (i.e., with no father) Afterwards with Uranus, she gave birth to the Titans, as Hesiod tells it:
She lay with Heaven and bore deep-swirling Oceanus, Coeus and Crius and Hyperion and Iapetus, Theia and Rhea, Themis and Mnemosyne and gold-crowned Phoebe and lovely Tethys. After them was born Cronos the wily, youngest and most terrible of her children, and he hated his lusty sire.
According to Hesiod, Gaia conceived further offspring with Uranus, first the giant one-eyed Cyclopes: Brontes ("Thunder"), Steropes ("Lightning") and Arges ("Bright"); then the Hecatonchires: Cottus, Briareos and Gyges, each with a hundred arms and fifty heads.As each of the Cyclopes and Hecatonchires were born, Uranus hid them in a secret place within Gaia, causing her great pain. So Gaia devised a plan. She created a grey flint (or adamantine) sickle. And Cronus used the sickle to castrate his father Uranus as he approached Gaia to have intercourse with her. From Uranus' spilled blood, Gaia produced the Erinyes, the Giants and the Meliae (ash-tree nymphs). From the testicles of Uranus in the sea came forth Aphrodite.
By her son Pontus, Gaia bore the sea-deities Nereus, Thaumas, Phorcys, Ceto, and Eurybia.
Because Cronus had learned from Gaia and Uranus that he was destined to be overthrown by one of his children, he swallowed each of the children born to him by his Titan sister Rhea. But when Rhea was pregnant with her youngest child, Zeus, she sought help from Gaia and Uranus. When Zeus was born, Rhea gave Cronus a stone wrapped in swaddling-clothes in his place, which Cronus swallowed, and Gaia took the child into her care.
With the help of Gaia's advice, Zeus defeated the Titans. But afterwards, Gaia, in union with Tartarus, bore the youngest of her sons Typhon, who would be the last challenge to the authority of Zeus.
Info borrowed from Wikipedia