The first person we know who realized the Earth couldn't be flat was the Greek philosopher Anaximander. Around 560 B.C., he suggested that the shape of the Earth was a cylinder. By 350 B.C., the concept of a spherical Earth was so satisfying and free of paradox that it was generally accepted by scholars even in the absence of direct proof. Eighteen more centuries would pass before there was a direct proof, in the form of Ferdinand Magellan's expedition to circumnavigate the globe. (source)

The true size of the Earth was known seventeen and a half centuries before it was first circumnavigated. In 230 B.C., the Greek philosopher Eratosthenes worked out its circumference of 25,000 miles by studying shadows cast by the sun in both Alexandria and Syene on the day of the summer solstice. (source)

Aristotle.

Aristotle provided the first conclusive argument for a spherical earth when he noted during a lunar eclipse that the shadow the earth cast on the moon was circular.

Claudius Ptolemy, a second-century astronomer working in Alexandria, Egypt, wrote thirteen volumes on his observations that were so influential that they came to be known as the Almagest, Arabic for "the greatest". Ptolemy's theories, which held that the Earth stood still in the heavens while the moon, sun, and planets moved around it and that the stars sat in a concave dome that arched over the universe, were completely wrong; however, the influence of these theories held back the science of astronomy for nearly 1,500 years. (source)

The Earth's atmosphere is 78% nitrogen, 21% oxygen, 1% argon, and traces of other gases.

In 1928, the German engineer Herman Sörgel proposed increasing the land mass of Europe and Africa by draining the Mediterranean Sea. By building a dam across the Strait of Gibraltar, the current from the Atlantic Ocean would be blocked and the water level of the Mediterranean would drop by about 1 metre per year. After 100 years, the water levels would be so low that there would be 223,000 km² of reclaimed land. Naturally, this proposal never got off the drawing board.

Christopher Columbus was not the only person of his time who believed the world was round. Since the twelfth century, educated people had been aware of the earth's actual shape. Where Columbus differed with the educated people of his time was that he thought the world to be much smaller than it actually was. He believed the westward distance from Spain to Asia to be around 2,500 miles, only around one-fifth of the true distance of around 12,000 miles. Had America not been in his way, Columbus' expedition would have ended in death on the endless sea. (source)

At least fifteen major geological catastrophes have occurred in the Earth's past, each marked by the extinction of certain dominant species.

On a clear day, you could see about 4½ kilometres if the horizon were unobstructed.

The eruption of the volcanic island of Krakatoa, in 1883, was so violent that it was heard 4,600 kilometres away, on Rodriguez Island in the Indian Ocean.

The current population of Earth is over 7,000,000,000. Around 1900 there were only 1,600,000,000 people, meaning that Earth's population has more than quadrupled in slightly over 100 years' time. (source)

The oldest rock on the earth is 3,960,000,000 years old. It is a grain of zircon found in much younger rocks near Great Slave Lake, in Canada's Northwest Territories. The oldest rock formation, in western Greenland, is dated at about 3,800,000,000 years.

The amount of water on Earth has remained the same since the planet was created some 4,600,000,000 years ago. (source)

Plants make up at least 90% of the mass of living things on Earth.

The earth's rotation is slowing down. In the Late Cretaceous period, around 85 million years ago, the earth rotated so much faster than it does now that a year consisted of 370.3 days, and in the Cambrian era, around 600 million years ago, a year consisted of about 425 days. Of course, the length of the day in the past would have been shorter than it is today. (source)

Venus, not Earth, is the best-mapped planet in the solar system, with 98% of its surface mapped. On the other hand, large portions of the Earth's ocean floor have not been mapped.

Less than three percent of all water on Earth is freshwater (usable for drinking) and of that amount, more than two-thirds is locked up in ice caps and glaciers. (source)

There are more than 326 million trillion gallons of water on Earth. (source)

The oceans of Earth contain about 496,370,000 cubic miles of water. (source)

At any given moment, there are 1,800 thunderstorms occurring somewhere on Earth. This amounts to 16 million storms each year. Lightning strikes the earth over 5,000 times each minute. (source)

If all the ice in glaciers and ice sheets melted, the sea level would rise by about 80 meters—about the height of a 26-storey building. (source)

Around the world, the ozone layer averages about 3 millimeters (1/8 inch) thick, approximately the same as two pennies stacked one on top of the other. (source)

Lake Baikal in Russia is the world's deepest lake, being as deep as 5,712 feet (over one mile) in places. Even though Lake Baikal is only the seventh-largest lake in the world by area, it is the world's largest lake by volume due to its depth. It contains about 20% of the world's liquid surface freshwater. (source)