Earth is called the "blue planet" for its abundant water supply and unlike other bodies in the solar system, liquid water is abundant on Earth, allowing millions of species to evolve and thrive, according to a Russia Today report.
It is known that about 71% of the Earth's surface is covered by water, and 96.5% of the planet's water supply is found in the oceans, according to the US Geological Survey (USGS).
But the water doesn't just stay below, as as part of the water cycle (also called the hydrological cycle), it moves into the atmosphere. Put simply, there are billions of gallons of water, mostly in the form of steam, in the sky right now, and if it all fell at once, it would cause some major problems for millions of people.
According to the US Geological Survey, the volume of all water on Earth is estimated at 332.5 million cubic miles (1.4 billion cubic kilometres).
More specifically, one cubic mile of water will contain approximately 1.1 trillion gallons, enough to fill 1.66 million Olympic-size swimming pools.
As a result of the hydrologic cycle, the Earth's water does not stay in one place for long. It evaporates, turns into steam, condenses to create clouds, and then returns to the surface in the form of precipitation. And then the cycle starts again. The evaporated water remains in the atmosphere for 10 days, according to Encyclopedia Britannica. This means that the atmosphere is actually immersed in water vapor.
“On average, there is about 30 mm of rain in the form of vapor available to fall on any point on the Earth's surface,” says Frederic Fabri, Director of the Stewart Marshall Radar Observatory and Associate Professor of Environment and Director of the Department of Atmospheric and Oceanic Sciences at McGill University in Canada. 25 kilograms of water per square metre, mostly in the form of steam.”
Fabri explained that given that the Earth's surface area is about 197 million square miles (510 million square kilometers), there are about 37.5 million gallons of water in the atmosphere. He added that if all this mass fell at once, it would raise the level of the global ocean by about 3.8 cm. Although all this steam falling at once is unlikely, such a dramatic rise in sea level is likely to have disastrous consequences.