Earth’s water: It came from outer space

Scientists believe that most of Earth’s finite water supply was brought here early in Earth’s history.

They think icy comets and asteroids bombarded the young Earth for hundreds of millions of years.

Bob Kandel: And that brought water mostly in the form of ice in these comets and meteorites and so on to the Earth that was forming. Now the impacts must have heated things up, some of that must have evaporated but eventually there was so much water vapor in the atmosphere it would have rained out.

That was Bob Kandel, a senior scientist at the National Scientific Research Agency of France and author of a book about Earth’s water. The basic stuff needed to make water – hydrogen and oxygen – are common elements in the universe.

Yet Earth is unique in our solar system for being a water planet. Oceans cover 70% of the Earth’s surface, and every living thing consists in large part of water. We continuously lose a little water to space from our outer atmosphere. And most scientists think the process that brought us water originally – the bombardment by comets and asteroids – has for the most part stopped.

That’s why nowadays the care of the 3% of our planet’s water that’s usable by humans is one of the major challenges of the 21st century.

Our thanks to:
Robert Kandel
National Scientific Research Agency
France