1. The Earth is not a perfect sphere. It's actually an oblate spheroid, thanks to a a slight equatorial bulge (the difference between the equatorial and polar diameters).
2. Gravity changes across the surface of the Earth — so dieters might want to avoid the poles, where you weigh 0.5 percent more than at the equator. This gravity disparity is largely due to that equatorial bulge creating non-uniform distances from points on the planet's surface to center of the Earth, and to the fact that the Earth spins.
3. The oceans, which cover almost 71 percent of the Earth's surface, contain close to 20 million tons of gold.
4. Humans have explored less than 10 percent of the Earth's vast oceans. Get on it, James Cameron.
5. The Earth's atmosphere is composed of five main layers, and the higher up you go, the thinner the atmosphere gets; that's why 75 percent of the atmosphere's mass is in the troposphere, the lowest layer and the place where weather occurs.
6. The atmosphere is responsible for auroras — which occur when solar wind particles hit atoms in the upper atmosphere of the Earth, creating beautiful displays of light. Red and blue auroras are caused by the excitation of nitrogen atoms, while green auroras and brownish-red auroras are from the excitation of oxygen.
7. The Earth's softest known mineral is talc. (Why do you think we use it to powder ourselves?) Talc is used in a variety of ways, including as a glaze in ceramics and as a filler in paper.
8. The Earth's tectonic plates, which collide with each other and are responsible for everything from earthquakes to mountains being formed, also play a vital role in maintaining the planet's carbon balance and thus, allowing life to thrive.
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