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According to the theory, our Solar System began about 4.57 billion years ago, as a giant cloud of molecular GAS and DUST.
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Scientists have not proven how, but the giant cloud collapsed within itself.
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From this collapse, pockets of dust and gas began to collect in the denser regions. This also formed PLANETESIMALS which are objects which solidify themselves with other objects.
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As the denser regions began to collect more and more matter, the cloud began to SPIN, while increasing pressure causing it to heat up.
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Most of the material formed a ball in the center, while the rest flattened out around it. The ball in the center formed the Sun, while the rest formed the PROTOPLANETARY DISK.
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Eventually, young planets were formed from small condensed pieces of matter. This happened one piece crashing nother to create larger pieces.
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Due to their higher boiling points, only metals and silicates could exist in solid form closer to the Sun, and these would eventually form the TERRESTRIAL PLANETS of Mercury, Venus, Earth, and Mars.
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Because the atmosphere allowed for gaseous planets to form, the GAS GIANTS, Jupiter, Saturn, Uranus, and Neptune formed of gas and small pieces of matter.
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Debris that never became part of a planet, became objects such as asteroids, CONDENSING and COLLIDING together to form larger asteroids.
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After 50 million years, the pressure and density of hydrogen in the middle of the PROTOSTAR became strong enough for it to begin thermonuclear fusion, meaning two or more nuclei FUSED together forming one. This caused the Sun to become the main-sequence star. After this, the Solar Wind swept away any remaining dust and gas, ending the planetary formation process in the SOLAR NEBULA.
