Earth is the third planet from the Sun. It formed over 4.5 billion years ago and weighs approximately 6.58 billion trillion tons. Earth is not a perfect sphere, but an oblate spheroid, “squashed” a little at the North and South poles. The equatorial diameter is about 7,926 miles, but the polar diameter is 7,899.86 miles. Earth’s spinning molten core produces the magnetosphere, a magnetic shield around the planet which largely protects the atmosphere from being blown away by solar winds.