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The length of Earth's day is increasing. When Earth was formed 4.6 billion years ago, its day would have been roughly six hours long. By 620 million years ago, this had increased to 21.9 hours. Today, the average day is 24 hours long, but is increasing by about 1.7 milliseconds every century. The reason? The moon is slowing down Earth's rotation through the tides that it helps create. Earth's spin causes the position of its tidal ocean bulges to be pulled slightly ahead of the moon-Earth axis, which creates a twisting force that slows down Earth's rotation. As a result, our day is getting longer — but not long enough to make a difference to your busy schedule.

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About 600-800 million years ago, Earth underwent several extreme climate changes known as ice ages. The climate became so cold that some scientists believe Earth nearly or completely froze several times; this is known as the "snowball Earth" theory. There may have been four such periods of alternate freezing and thawing, triggered by reductions in greenhouse gases such as methane and carbon dioxide, during which Earth would have been covered by glacial ice from pole to pole. Because most of the sun's energy would have been reflected back into space by ice, the planet's average temperature would have been about -50 degrees Celsius (-74 degrees Fahrenheit), with the equator akin to Antarctica today. If snowball Earth did exist — a point that is hotly contested — luckily we weren't around to feel the chill, as only microscopic and simple organisms existed then.

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If Earth were a perfect sphere, its gravitational field would be the same everywhere. But in reality, the planet's surface is bumpy, and water flow, ice drift and the movement of the tectonic plates beneath Earth's crust all change the pull of gravity. These variations are known as gravity anomalies. A mountain range such as the Himalayas causes a positive gravity anomaly — gravity is stronger there than it would be on a featureless perfectly smooth planet. Conversely, the presence of ocean trenches, or dips in the land caused by glaciers millennia ago, leads to negative gravity anomalies. NASA's GRACE (Gravity Recovery and Climate Experiment) mission, orbiting above us, is mapping Earth's gravitational field in unprecedented detail.

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4. In the past, sea levels were very different

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4. In the past, sea levels were very different

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The most recent advance of ice on planet Earth began about 70,000 years ago, ended 11,500 years ago and reached its farthest extent 18,000 years ago. During this time, glaciers and sheets of ice carved out the basins of the Great Lakes and blocked rivers, diverting the courses of the Mississippi and other rivers in the U.S. So much water was trapped as ice that sea levels dropped by as much as 120 meters (390 feet), exposing parts of what is now the ocean floor. Earth's sea level has also been up to 70 meters (230 feet) higher in the past. During the last interglacial period, the sea was actually 5 to 7 meters (16 to 23 feet) higher than it is today.

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All stars, like our sun, age and eventually die. As the sun exhausts its supply of hydrogen, it will collapse under gravity, ultimately ballooning into a red giant that is 100 times bigger and 2,000 times more luminous, vaporising Earth in the process. But don't worry; it won't happen for about five billion years.

One option is to leave the planet before this happens, but that would require as yet unimagined technology and a habitable destination. The other possibility is that, over the next few billion years, a passing star could disrupt Earth's orbit and kick it away from the sun. Scientists have suggested the odds of this are one in 100,000 — better than winning the lottery. Unfortunately, left without a sun our descendants would probably end up freezing to death.

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It's not just an old wives' tale: under the right conditions, the calm before the storm really does exist. As a storm draws in warm, moist air — its fuel — from the surrounding atmosphere, it leaves a low-pressure area behind. Air is carried up into the storm cloud, and some of it is forced upwards by powerful drafts. These updrafts remove the hot air and push it out over the sides of the highest storm clouds, which can be up to 16 kilometers (10 miles) high. As the air then descends, it becomes warmer and drier and therefore more stable. It blankets the region below and stabilizes the air contained within, causing people within that region to notice a calm before the storm.