‘How inappropriate to call this planet Earth when it is quite clearly Ocean.’
Arthur C. Clarke
Of all the planets in the universe that humans have observed, Earth is the only one with liquid water on its surface. Even though water is found as ice and gas elsewhere in our solar system – Europa, one of Jupiter’s moons, is thought to have twice as much water as our planet – Earth is the single place in the known universe with oceans. What is it about Earth that makes it so special?
Though we may take oceans as a given, we’re really pretty lucky to have them. In fact, Earth hasn’t always looked like it does now; it wasn’t always covered in water. Four billion years ago – long before dinosaurs existed, when Earth was just 700 million years old – our planet was hot, rocky and not exactly life-friendly. There was no water on its surface and no atmosphere to protect it. It was around this time that Earth began gathering water on its surface, and it’s thought to have come from two distinct places: within the planet and outer space.
Water From Within
Some of our planet’s water originated as steam escaping from molten rock and volcanoes. At this early stage in Earth’s history it would have been too hot for liquid water to settle on our planet’s surface. It was over millions of years as the globe cooled down enough – below 100 ⁰C – that rain began to fall, forming rivers and collecting in hollows. Water moving across the land dissolved minerals, making it salty. This was the birth of the first oceans. (It was also at this time that other gases escaping from Earth’s crust and gathered to form the atmosphere.)
Water From Without
But not all Earth’s water comes from terrestrial sources, part of it is thought to have come from outer space. Comets colliding with Earth carried plenty of water and other gases, releasing them at the surface. It’s likely these impacts – much more common in the early solar system – contributed significantly to the planet’s water reservoir.
However water got here, we’re lucky that it’s liquid water, which can pool into hollows and form oceans. This is thanks to Earth’s auspicious position in the solar system. Any closer to the sun and the water would all be gas, any further and it would be solid ice. Few planets have been found that occupy this unique zone where the temperature is just right. Earth is the only one with liquid water on its surface.
As water is thought to be a prerequisite for life, it’s because of our blue planet’s special situation that we’re around to appreciate the beauty of the oceans – the only ones known of!
Want to know more? Check out this great National Geographic video on YouTube.
Lisa Boonzaier is a young woman who loves the ocean: its wild, mercurial character; its colour; its life; its waves; everything. She hopes to contribute as much as she can to saving our oceans as we know them before they’re irreversibly changed.