A new study has brought fresh ideas about where Earth’s water came from and how it shaped our planet early on. This research suggests that before a massive impact, which created the Moon, Earth was a dry place. If this is true, then Earth-like planets that can support life might be far less common in the universe.
The origin of Earth’s oceans has puzzled scientists for centuries. Some early thinkers, like Isaac Newton, believed that comets brought water to Earth. More recent studies both support and challenge this idea. Initial conditions on Earth were so hot that water likely evaporated and escaped into space. So, for water to be here now, it had to come from somewhere else, either trapped deep inside or delivered later, possibly by comets or asteroids.
Research now points to a different theory: instead of a steady flow of comets, a single major event may have delivered the water. Scientists have noticed that neighboring planets, like Mercury and Mars, lack key elements that make life possible. In fact, these planets have very few volatile elements, which are crucial for life.
Dr. Pascal Kruttasch and Professor Klaus Mezger from Universität Bern used manganese as a proxy to study the early Earth’s water. They compared isotopes of manganese and chromium from asteroids and Earth rocks. Their findings suggest that our planet formed quickly, within three million years after the Solar System started. Initially, Earth had similar low levels of volatiles as other rocky planets.
Their research points to a specific time, about 4.561 billion years ago, when Earth’s chemistry shifted. The team measured radioactive manganese-53, which breaks down to chromium-53 over a specific timeframe. Kruttasch noted that this data helps pinpoint important events in Earth’s early history.
They concluded that rather than a continuous influx of water through time, Earth’s volatiles likely arrived in one significant event—from an object similar in size to Mars, named Theia. This colossal impact would have sent a massive amount of debris into orbit, forming the Moon. It’s believed that Theia carried with it essential volatile elements. Although much of this material might have boiled away from the extreme heat of the collision, enough would have remained to create oceans on Earth.
The researchers estimate that around 90% of Earth’s material comes from the proto-Earth before this collision. Just 10% is from Theia, with a tiny fraction arriving later. Kruttasch summed it up: “The proto-Earth was a dry rocky planet, and it was the collision with Theia that brought the elements necessary for life.”
This implies that the chance of Earth being a habitable planet is incredibly slim. The size of our Moon and the unique nature of our past collisions may be key factors for advanced life. Some experts have pointed out that the circumstances leading to life on Earth are rare. Our planet may be one of only a few—if not the only—places where such conditions occurred.
The implications could be vast. While simple life might exist elsewhere, advanced civilizations may be exceptionally rare. This contributes to the ongoing mystery surrounding the Fermi Paradox, which questions why we haven’t found evidence of extraterrestrial life despite the vastness of the universe. The new insights underscore how unique Earth might truly be.
For those interested in exploring this further, the complete study is available open-access in Science Advances here.
