Considering the Big Bang Theory, how was the earth formed?
In about 13.8 billion years (BY) since Big Bang event, stars, star clusters and galaxies were formed at different periods, Sun is about 4.6 BY old. Earth was formed a little later, 4-4.6 BY ago.
BB explosion generated atoms/particles/elements/, for matter that
later became constituents of space bodies, in the order, stars, star
clusters and galaxies.
A star system evolved in the gravitational sphere of every star.
Earth is the Sun system.
Sun is believed to have been born about 4.6 billion years (BY) ago.
Earth was formed from the planetesimals in a spherical shell around
Sun, about 4 - 4.6 BY ago.