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Planetary accretion occurs as gravitational attraction draws objects together in space. These objects may be dust, gas, plasma (ionized "gas"), debris from comets, etc.
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An asteroid smashed into Earth, which melted most of the Earth and the asteroid itself. These materials was thrown out into orbit. Over time, this material smashed together to form Moon. The moon formed 70 million years after Earth formed.
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A nearby star exploded about 4.5 billion years ago, sent a shock wave through the dust cloud, which increased the rate of spin. Smaller concentrations of mass rotating around the center formed the Earth.
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The end of Heavy Bombardment is a period that highly intensified asteroid impacts taking place between 4.1 to 3.8 billion years ago.
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At first, Earth was molten and lacked an atmosphere and oceans. Gradually, the planet cooled and formed a solid crust. As the planet continued to cool, volcanoes released gases, which eventually formed an atmosphere.
