The best, and widely accepted theory, is that the Earth formed about 4.5 billion years ago, along with the rest of the solar system. I can describe the process in more details if you are interested, but in short, there was a huge, huge cloud of gas and dust which contracted on itself and formed the Sun and the planets (and all the rest of the solar system stuff). All the elements that are found on Earth and in the Sun and in the rest of the solar system, come from that original cloud.
It’s called the Solar Nebula model. The Sun and the planets formed from a nebula of gas and dust. This is an example of an evolutionary model in which the process occurred slowly without requiring an unusual event.
The Sun and the planets formed at the same time from a contracting rotating cloud of gas which was roughly spherical to begin with. As the cloud rotated it became flatter. The resulting disc sped up and flattened. Gravity caused matter to concentrate at the centre of the disc. That region became hotter, and eventually formed the Sun. In other regions of the disc, beyond that central parts, there were pockets of denser material which became larger and larger by simply colliding with each other and sticking together – this is called accretion.
Accretion of matter made these clumps grow into larger bodies, ranging in diameter from a few centimetres to several kilometres – they’re called planetesimals. Gravity began then to play an important role. Planetesimals continued to grow to form proto-planets, more massive objects that were the next stage in the formation of the planets.
The largest proto-planets had the greatest gravitational attraction: they collected other bodies most effectively. They grew fastest by sweeping up smaller bodies. Planet sized bodies were formed.
This model explains the disk shape of the solar system, and why almost everything rotates in the same direction.
So we are made of the elements that were originally in this cloud of gas and dust. Where did the dust and gas originally come from? The Big Bang (at the birth of the Universe) gave roughly 73% hydrogen, 25% helium and about 2% heavier elements. The Sun still has this composition (almost). Heavier elements were produced by other stars which exploded and enriched our solar nebula with all the other elements. As a result, the nebula was mainly hydrogen and helium with much smaller amounts of the heavier elements coming from dead stars that had exploded before our solar system formed.
Comments
Liesel_G commented on :
Could you describe it in more detail please?
Nicolas commented on :
It’s called the Solar Nebula model. The Sun and the planets formed from a nebula of gas and dust. This is an example of an evolutionary model in which the process occurred slowly without requiring an unusual event.
The Sun and the planets formed at the same time from a contracting rotating cloud of gas which was roughly spherical to begin with. As the cloud rotated it became flatter. The resulting disc sped up and flattened. Gravity caused matter to concentrate at the centre of the disc. That region became hotter, and eventually formed the Sun. In other regions of the disc, beyond that central parts, there were pockets of denser material which became larger and larger by simply colliding with each other and sticking together – this is called accretion.
Accretion of matter made these clumps grow into larger bodies, ranging in diameter from a few centimetres to several kilometres – they’re called planetesimals. Gravity began then to play an important role. Planetesimals continued to grow to form proto-planets, more massive objects that were the next stage in the formation of the planets.
The largest proto-planets had the greatest gravitational attraction: they collected other bodies most effectively. They grew fastest by sweeping up smaller bodies. Planet sized bodies were formed.
This model explains the disk shape of the solar system, and why almost everything rotates in the same direction.
So we are made of the elements that were originally in this cloud of gas and dust. Where did the dust and gas originally come from? The Big Bang (at the birth of the Universe) gave roughly 73% hydrogen, 25% helium and about 2% heavier elements. The Sun still has this composition (almost). Heavier elements were produced by other stars which exploded and enriched our solar nebula with all the other elements. As a result, the nebula was mainly hydrogen and helium with much smaller amounts of the heavier elements coming from dead stars that had exploded before our solar system formed.