One line of evidence suggesting water on Earth came from comets is the similarity in the isotopic composition of water found on comets and Earth, specifically with regard to the ratio of deuterium to hydrogen. This similarity implies a common origin. Additionally, the discovery of organic compounds, including amino acids, on comets such as Comet Halley further supports the idea that comets brought water to Earth, as these compounds are essential for the development of life. Furthermore, the analysis of the Rosetta mission's data, studying the composition of comet 67P/Churyumov-Gerasimenko, showed that the water on the comet is chemically similar to Earth's oceans, further suggesting a link between comets and Earth's water.
