The Origin of Water on Earth: Scientific Theories and Discoveries
- Martin Colognoli
- Jun 4
- 4 min read
Water is an essential resource for life on Earth, but its origin remains a subject of scientific debate. How did it appear on our planet? Was it present from its formation or brought by celestial bodies?
In this article I propose to explore the main theories and recent discoveries on this fundamental mystery.
Introduction to the question of the origin of terrestrial water.
Importance of water for life on Earth
Water covers approximately 70% of the Earth's surface and plays a key role in climate regulation, continent formation, and biological evolution. It is the universal solvent, essential for the chemical reactions that enabled the emergence of life.
The oceans are home to over 80% of the world's biodiversity, and every terrestrial organism depends directly or indirectly on this vital resource. But where does this water come from that makes our planet so unique?
Scientific issues related to its origin
Understanding the origin of terrestrial water allows us to answer several fundamental questions:
How did the Earth form and differentiate?
What conditions favored the emergence of life?
Is water common in the universe, and therefore a sign of life elsewhere?
These issues have led to several hypotheses, which we will explore.
Main theories about the origin of water
Earth accretion theory
According to this hypothesis, water was present from the formation of the Earth, trapped in the minerals of the mantle. It would then have been released by volcanic activity, contributing to the formation of the oceans.
Enstatite chondrites, meteorites with a composition close to Earth's, contain significant traces of hydrogen, suggesting that our planet may have accumulated water from its inception.
Recent evidence: A study published in Science (Piani et al., 2020) demonstrated that these meteorites contain up to 0.5% water by mass, which would confirm this hypothesis.
Theory of comets and asteroids
Another theory proposes that water was brought by comets and asteroids after Earth's formation. These ice-rich celestial bodies would have released their water upon collision with our planet.
Isotope analysis: Scientists compared the deuterium-to-hydrogen (D/H) ratio of Earth's water with that of different comets. The result: some comets don't match, while some main-belt asteroids have a closer ratio.
Asteroids, not comets, would therefore be more plausible candidates.
Other hypotheses and models
Other models suggest that water could:
Coming directly from the solar nebula, trapped on dust grains.
Resulting from chemical interactions between hydrogen and oxygen in deep Earth rocks.
Recent discoveries and scientific advances
Isotopic analyses and their implications
Studies of water's isotopic ratios allow us to trace its origin.
Latest discoveries:
Carbonaceous meteorites contain water with a D/H ratio close to that of the oceans.
Some comets in the Jupiter family also exhibit a similar isotopic signature.
This reinforces the idea that terrestrial water may have originated from a mixture of sources rather than a single origin.
Space missions and new data
Recent explorations have yielded fascinating clues:
Rosetta Mission (ESA, 2014)
Analyzed comet 67P/Churyumov-Gerasimenko.
Revealed a D/H ratio very different from that of terrestrial water.
Confirms that comets are not Earth's primary water suppliers.
ALMA Observations (2023)
Detected water vapor in protoplanetary disks, proving that water has been present since the formation of planets.
These results support the idea that water was already present on Earth from its origin.
Implications for the search for life elsewhere
Water on other planets and exoplanets
If Earth's water came from space, then it could be common on other planets.
Concrete examples:
Mars: presence of water in the form of ice and ancient lakes.
Europa (Jupiter's moon): ocean under the ice, potentially habitable.
Enceladus (moon of Saturn): water geysers rich in organic elements.
Perspectives for astrobiology
These discoveries are major for astrobiology:
Water seems to exist elsewhere in the universe .
Conditions favorable to life could be common .
Future space missions will target these aquatic worlds (like Europa Clipper and Dragonfly).
We may be closer than ever to discovering another form of life .
Conclusion
The origin of Earth's water remains a fascinating subject, with several theories coexisting. Was the water there from the beginning, or did it come from space? The latest scientific advances show that it comes from a mixture of several sources, including terrestrial accretion and meteorite deposits.
This quest goes beyond Earth: by better understanding where our water comes from, we increase our chances of finding life elsewhere in the universe.
Scientific references
Piani, L., Marrocchi, Y., Rigaudier, T., Vacher, LG, Thomassin, D., & Marty, B. (2020). Earth's water may have been inherited from material similar to enstatite chondrite meteorites. Science, 369(6507), 1110-1113.
Altwegg, K., Balsiger, H., Bar-Nun, A., Berthelier, JJ, Bieler, A., Bochsler, P., & Le Roy, L. (2015). 67P/Churyumov-Gerasimenko, a Jupiter family comet with a high D/H ratio. Science, 347(6220), 1261952.
Cleeves, LI, Bergin, EA, Alexander, CMO, Du, F., Graninger, D., Öberg, KI, & Harries, TJ (2014). The ancient heritage of water in the solar system. Science, 345(6204), 1590-1593.
Raymond, S.N., Izidoro, A., & Mordasini, C. (2018). Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn's growth. Icarus, 301, 100-114.
Marty, B. (2012). The origins and concentrations of water, carbon, nitrogen and noble gases on Earth. Earth and Planetary Science Letters, 313, 56-66.
