Earth: The third planet from the Sun. Its blue and green hues verified by Apollo 17 when they landed on the moon in 1972. It is the only "known" planet to contain life, as we know it. This oblate spheroid with its varying layers of solid and molten rock spins about its axis approximately 1000 miles per hour, while orbiting the Sun at about 67,000 miles per hour
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. Earth is overwhelmed with life, from the microscopic bacillus to the gigantic blue whale. But how? But why? What makes this planet so unique, different from the other eight in our solar system? In order to understand how Earth became the habitable planet that it is today, we have to go back. Way, way back to the beginning of the story, to the conception of Earth.
In the far reaches of space existed a single condensed point of matter. About fourteen billion years ago this point of matter exploded shooting protons, electrons, neutrons, positrons, neutrinos, and photons everywhere. As this superheated mass began to cool the subatomic particles began to join one another forming neutral atoms
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. These neutral atoms continued to coalesce to eventually form the Sun and the planets. About 4.5 billion years ago, as Earth was finalizing its accretion, a Mars-sized body collided with it. The intense heat from the impact transformed Earth into a molten body of rock. The pieces that dislodged from Earth and what remained of the body, combined to form the Moon
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. As the Earth continued to form, the heavier elements sank and the lighter elements rose into the atmosphere. The lightest of all, hydrogen escaped into space, leaving behind an atmosphere abundant in carbon dioxide, sulfur dioxide, methane, ammonia, and water vapor. Earth's early atmosphere contained very little oxygen
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. With all the pieces in place the planet now had everything it would need for the evolution of life to proceed.
