Earth is not truly a "Sphere" but rather an "Oblate Spheroid" – flattened slightly at the poles and bulging at the equator by about an extra 43 kilometers. Gravity is slightly greater at the poles than at the equator.
We know more about space than we know about the bottom of Earth's oceans.
Earth is about four times the size of it's Moon, and the volume of the Moon is the same as that of the Pacific Ocean.
About 0.01% of the world's water is present in rivers and lakes, and 4.34% is fresh groundwater. 1.65% of Earth's water is "locked" in glaciers or polar icecaps, and a whopping 94% is salt water. If all the salt were to be extracted from the oceans and seas? There would be enough to cover all the continents five feet deep.
Of all known forms of animals life ever to inhabit the Earth, only about 10 percent still exist today.
Earth's rotation speed is at its maximum in late July, early August and at its minimum in April. The difference in the length of the day is about 0.0012 seconds. Rotation is also slowing down, and an extra second is added to atomic clocks every few years. Millions of years ago, a solar day on Earth was 20 hours long. It is believed that, after a few million more years, Earth days will be 27 hours long.
The length of time it takes for Earth to orbit around the Sun is 365 and a quarter days, or 365.2564 to be exact. It is that extra .2564 days that creates the need for leap years.
To make up the extra quarter which isn't counted, we add extra day in every year divisible by 4 – 2004, 2008, etc. – unless it’s divisible by 100 (1900, 2100, etc)… unless it’s divisible by 400 (1600, 2000, etc). The next Leap Year is 2012.
On average, nearly a thousand tons of meteor dust falls to Earth's surface each day. Most burn up as they fly through the atmosphere, but those making it to the ground are then called meteorites. About 900 meteorites land per year around the world, but most land in Earth's oceans.
Colloquially, most people use the words "air" and "oxygen" interchangeably, but Earth's atmosphere nearest the crust of the planet contains 78% nitrogen and only 21% oxygen. Argon at 0.9%, carbon dioxide at 0.033% and other minute gases account for the rest.
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