The Earth seen from space is a beautiful blue sphere, filled with water – this makes our planet unique in the Solar System and is essential for life. However, the origin of Earth’s water remains a mystery that scientists have struggled to understand for centuries.
A popular theory is that Earth’s water came from ice-laden comets and asteroids that collided with our planet during the so-called *Late Heavy Bombardment*, which occurred about 4.1 to 3.8 billion years ago. These bodies, known as “dirty snowballs,” brought ice, rock, and dust, delivering water to Earth through repeated collisions.
The traces of these collisions can be seen in craters on the surface of the Moon, which have not been erased by geological processes like those on Earth.
Additionally, it is hypothesized that water was trapped in the Earth’s mantle from the time the planet formed. This water was released through volcanic eruptions, which sent water vapor into the atmosphere, which then condensed into rain and formed the first oceans. This is a process called *outgassing*, which over time may have contributed a significant amount of water to Earth.
To determine the origin of water, scientists analyze the ratio of deuterium to hydrogen in water. Water from different sources such as comets, asteroids, or water in the Earth’s mantle has different ratios of deuterium. By comparing these ratios, researchers can assess where Earth’s water came from.
Some studies have shown that the ratio of deuterium in Earth’s water is similar to that of some comets and asteroids, which supports the hypothesis that these celestial bodies played a role in bringing water to the planet.
Still, both theories—water from outer space and water from within the Earth’s mantle—could be correct. A combination of meteorite impacts and volcanic eruptions could have helped Earth accumulate vast amounts of water, creating an environment that could support life.
Studying the origin of water on Earth not only helps us understand the history of the planet, but also helps determine the likelihood of water and life in outer space. The discovery of ice on the Moon, Mars, and the moons of Jupiter and Saturn suggests that water may be more common than we thought. The presence of liquid water would be an important indicator in the search for extraterrestrial life, as liquid water is considered a necessary condition for life.
Water is the source of life, the foundation of all life on Earth. Understanding the origin of water is an exploration of our own origins, of how Earth became the life-rich world we call home.
