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At first, our solar system was a rotating cloud of stardust. A nearby star exploded, and it sent a shock wave to the cloud of stardust. The majority of the mass was contained in the middle to form the Sun, while the smaller concentration of mass formed the rest of the planets, including Earth.
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Like the other planets in our Solar System, Earth was formed by the process of accretion where dust and other solids collided with each other to gradually form a bigger body. The collisions caused Earth to become very hot. The denser material was pulled closer to the core while the lesser remained on the crust. This separation is the reason why Earth has layers.
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It is suggested that the Moon was formed by a Mars-sized asteroid crashing onto Earth. The energy melted most of Earth and the asteroid. The asteroid with bits of Earth was thrown out of orbit and formed the Moon, over time. The Moon was formed about 70 million years after Earth.
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This period was when smaller, failed planets and asteroids scarred the surface of formed planets, including Earth.
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Around 4 billion years ago, water vapor was released onto the surface by volcanoes and formed oceans, which cooled down the Earth. The oceans then were very toxic.
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The heat loss from the inner core drove convection of the outer core, which then formed the magnetic field about 3.45 million years ago. The magnetic field deflect solar wind and allowed an atmosphere to form on Earth.
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According to recent research, the Earth's core was only formed about 1 billion years ago. The outer core is made of liquid iron that surrounds the inner core, which is solidified iron. It is unable to be liquid because the pressure and density of the planet and atmosphere it too great for it to become liquid.