No, the Earth was not a big fireball at birth. Instead, it formed through a process called accretion, where dust, ice, and small particles combined to form larger and larger bodies until they eventually coalesced into the planet we know today. As the Earth formed, its interior heated up due to the radioactive decay of elements such as uranium and thorium, as well as the energy released from the gravitational compression of the accreted material. However, the Earth did not reach the point of becoming a molten ball of fire; instead, it developed a molten iron core surrounded by a solid mantle and crust.